Interrelationships Between Energy Balance and Postpartum

8/2/2019 Interrelationships Between Energy Balance and Postpartum

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Interrelat ionsh ips Betw een Energy Ba lance and Postpa rtumReproduct ive Funct ion in Da i ry Cat t le

W . R . B U T L E R a n d R . D . S M I T HD e p a r t m e n t o f A n i m a l S c i e n c eCorne l l Un iv e rs i tyI t h a c a , N Y 1 4 8 5 3A B S T R A C T

G e n e t i c i m p r o v e m e n t o f d a i ry c o w sh a s m a r k e d l y i n c r e a s e d m i l k y i e l d o v e rt h e l a s t th r e e d e c a d e s . I n c r e a s e d p r o -d u c t i o n h a s b e e n a s s o c i a t e d w i t h r e d u c e dc o n c e p t i o n r a t e s ( 6 6 % i n 1 9 5 1 v e r s u s 4 0t o 5 0% s i n c e 1 9 7 5 ) . B e c a u s e c o n c e p t i o nr a t e i n d a i r y h e i f e r s h a s r e m a i n e d h i g h e r ,t h e m e t a b o l i c d e m a n d s o f h i g h e r p r o -d u c t i o n m a y b e r e l a t e d t o t h e d e c l i n e i nr e p r o d u c t i v e p e r f o r m a n c e i n c o w s . D u r -ing ea r ly l ac t a t i on , i nc reas ing d i e t a ryi n t a k e f a i l s t o k e e p p a c e w i t h r i s i n g m i l kp r o d u c t i o n . T h e r e s u l t a n t n e g a ti v e e n e r g yb a l a n c e a n d r a t e o f m o b i l i z a t i o n o f b o d yr e s e r v e s a p p e a r d i r e c t l y r e l a t e d t o t h ep o s t p a r t u m i n t e r v a l t o f i r s t o v u l a t i o n a n dl o w e r c o n c e p t i o n r a t e . D e l a y s in t h eo n s e t o f n o r m a l o v a r i a n a c t i v i ty , t h u sl i m i t in g t h e n u m b e r o f e s t r o u s c y c l e sb e f o r e b r e e d i n g , m a y a c c o u n t f o r t h e o b -se rved dec rease i n fe r t i l i t y . N ega t i vee n e r g y b a l a n c e p r o b a b l y a c t s s i m i l a r l y t ou n d e r n u t r i t i o n a n d m a y m a n i f e s t ind e l a y e d o v a r i a n a c t i v i t y b y i m p i n g i n g o np u l s a ti le s e c r e t i o n o f L H . L o w e r av ail-a b i l i ty o f g lu c o s e a n d i n s ul in m a y a l sod e c r e a s e L H p u l s a t i l i t y o r l i m i t o v a r i a nr e s p o n s i v e n e s s t o g o n a d o t r o p i n s . A l t e r -n a t i v e l y , r e le a s e o f e n d o g e n o u s o p i o i d s i na s s o c i a t i o n w i t h i n c r e a s i n g f e e d i n t a k e o ro t h e r l a c t a t i o n a l h o r m o n e r e s p o n s e s m a yp r o v i d e n e u r a l o r p i t u i t a r y i n h i b i t i o n o ft h e p u l s a t i l e L H p r o d u c t i o n t h a t i sr e q u i s i te f o r o v a r i a n f o l l i c u la r d e v e l o p -m e n t .

I N T R O D U C T I O NI n c o n s i d e r i n g t h e r e l a t io n s h i p s o f d i e t a r y

e n e r g y t o r e p r o d u c t i o n i n d a i r y c a tt le , t h e m o s t

Received August 31, 1987.Accepted December 21, 1987.

i m p o r t a n t p e r i o d i s e a r l y a n d p e a k l a c t a t i o nw h e n t h e d e m a n d f o r e n e r g y i s h i g h e s t . A c o wp r o d u c i n g 3 5 k g o f m i l k d a i l y r e q u i r e s t h r e et im e s m o r e e n e r g y f o r p r o d u c t i o n t h a n f o rb o d y m a i n te n a n c e . T h e e n e r gy re q u i re m e n t s o fa l a c t a t i n g c o w a r e m e t t h r o u g h a c o m b i n a t i o no f d i e t a ry i n t a k e a n d m o b i l i z a ti o n o f b o d yrese rves . D a i ry ca t t l e , hav ing bee n se l ec t ed fo rh i g h m i l k p r o d u c t i o n , c a n n o t m a i n t a i n ap o s i t iv e d i e t a r y e n e r g y b a l a n c e d u r i n g e a r l yl a c t a t i o n a n d m u s t m o b i l i z e b o d y r e se r v e s ( 9 ) .B e c a u s e t h e s h i f t f r o m n e g a t i v e t o p o s i t i v ee n e r g y b a l a n c e d u r i n g t h e c o u r s e o f e a rl yl a c t a t i o n m i g h t a f f e c t r e p r o d u c t i v e p e r f o r m -a n c e , a m a j o r o b j e c t i v e f o r t h i s p a p e r i s a na t t e m p t t o r e la t e t h e e n e r g e t ic s o r m e t a b o l i cd e m a n d s o f m i l k p r o d u c t i o n t o r e p r o d u c t i v ef u n c t i o n . S e c o n d , w e a d d re s s t h e i n t e r a c ti o n o ft h e r e l a t i v e a v a i l a b i l i t y a n d m o b i l i z a t i o n o fb o d y r e s e r v e s t o s u b s e q u e n t r e p r o d u c t i v ep e r f o r m a n c e . T h i r d w e p r o p o s e a w o r k i n gm o d e l f o r t h e i n t e r a c t i o n b e t w e e n n e g a t i v ee n e r g y b a la n c e a n d c o n t r o l o f g o n a d o t r o p i ns e c r e t i o n i n d a i r y c o w s .A c o m p r e h e n s i v e i n t e r n a t i o n a l s y m p o s i u mw a s h e l d i n 1 9 8 1 o n F a c t o r s i n f l u e n c i n g f e r-t i li t y i n t h e p o s t p a r t u m c o w ( 3 5 ) . T h e p r e s e n tt r e a t i s e w i l l e m p h a s i z e a n d u p d a t e t h e r e c e n tl i t e ra tu re .

I n t e r a c t i o n s B e t w e e n M i l kP r o d u c t io n a n d R e p r o d u c t i o nR e s e a r c h d u r i n g t h e p a s t s e v e r a l d e c a d e s h a s

y i e l d e d c o n f l i c t i n g r e p o r t s o n t h e p o s s i b l ei n t e r a c t i o n s b e t w e e n m i l k p r o d u c t i o n a n dr e p r o d u c t i v e p e r f o r m a n c e . S o m e o f t h e dis -c r e p a n c i e s a r e l i k e l y d u e t o d i f f e r e n t m e a s u r e so f r e p r o d u c t i v e p e r f o r m a n c e . N o n r e t u r n r a t e sa f t e r A I , p o s t p a r t u m d a y s o p e n , o r c a lv in gi n t e r v a l s a r e n o t g o o d m e a s u r e s , b e c a u s e t h em a n a g e m e n t d e c i s i o n s o f d a i r y p r o d u c e r s a r ec o n f o u n d e d w i t h b i o l o g i c a l e f f e c t s. A l t e r -n a t i v e l y , c o n c e p t i o n r a t e t o a r t i f i c i a l i n s e m i n a -t i o n i s n o t s u b j e c t t o t h e s a m e l i m i t a t i o n s a n d

1989 J Dai ry Sci 72 :7 67- 783 767


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768 BUTLER AND SMITHTABLE 1. Relationship of lactation to conception rate (CR) following artificial insemination.CR in Cows (%)1 CR in Herdmate

1 2 n Herifers (%) Milk yield vs. CR comparisons Reference66 45,000 No50 51 9750 Negative YesNegative Yes49" 56 212 Negative Yes50 307 Negative No51 2820 Nonsignificant No40 195,000 64 No41 48 2426 55 Nonsignificant No52 +11 400,000 66 Yes52 233,000 Negative No

(22)(76)(71)(21)(78, 79)(33)(63)(25)(20)(75)1 = First service, 2 = second service.

has been used in the large survey studies sum-marized in Table 1. The available info rmat ionsuggests that first service conception ratedeclined between 1951 and 1973 but hasremained relatively constant since then. Thestudies that include herdmate comparisons haveless confounding effects and overall dem-onstrate significant negative effects of milkyield on conception rate.The decline in conception rate from 66% in1951 (22) to an average of 50% in 1973 (76)occurred during a period when the averageannual milk production in the same populationof dairy cows increased by 1500 kg (33%). Thisrelationship is illustrated in Figure 1. Whenmilk production was considered, the overalldecline in average conception rate was ex-plained by the inverse relationship of con-ception rate to milk yield. Althou gh during thesame period the AI industry shifted from freshto frozen semen, fertility (60 to 90 d nonreturnrates) remained similar until after 1961 (56)and thus seems to have had little impact on thereduction in conception rate observed by 1973(76). A recent survey conducted in 1985indicates that while herd milk production hascontinued to increase, overall conception ratehas declined no further [Figure 1; (75)] . Asindicated in Table 1, conception rates in virgindairy heifers have remained as high as thoseoriginal ly report ed for cows in 1951. Becausefertility to AI was equal for heifers and cows in1954 (32), we conclude th at the decline inconception rates for lactating cows reflects the

effects of greater milk production, not geneticselection for lower fertility.

A final p oint concerning fertility in lactatingcows is the difference in conception ratesobserved for first versus second insemination.The increased rate at second service observed inseveral studies (Table 1) indicates that wi thsucceeding estrous cycles, increasing dayspostpartum or differences in stage of lactationmay have an important bearing on fertility.Although these factors are obviously con-found ed with tim e and not easily separated,they appear associated with another importantrelationship regarding fertility: that conceptionrate in lactating cows is related to the numberof ovulato ry cycles preceding inse minat ion (53,78, 81, 84, 88). On ce init iated , cyclic ovarianactivity in postpartum dairy cows seems tocontinue regularly. Hence, the reestablishmentof ovulatory cycles early after parturitionassures multiple estrous cycles prior to therecommended breeding period and in thismanner influences conception rate.

Linking the effects of lactat ion on fertilityto the number of preceding luteal phasessuggests important practical advantages to earlyreinit iatio n of o vulatory estrous cycles. This, inturn, has served to focus research attention onthe postpartum interval to first ovulation andon questions of possible dietary constraints tothe initiation of ovulatory cyclicity duringrapidly increasing milk production. However,before attempting to relate the effects ofdietary energy to postpartum reproduction, it

Journal of Dairy Science Vol. 72, No. 3, 1989


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SYMPOSIUM: INTERACTIONS OF NUTRITION AND REPRODUCTIONM i l k Pro d u c t i o n i n Ne w Yo rk DHI He rd s

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Y E A R S

Figure 1. Annual milk production for cows in New York herds under Dairy Herd Improvement testing(1950 to 1986). Conception rate (CR = 66%, *) for lactating cows in 1951 (22) is compared to: inset a showingthe inverse effects on CR (mean = 50%) of lactational milk yields (as deviations among herdmates, mean =6305 kg) in 1973 (76); and inset b showing CR (mean = 51%) by production among herds (not cows) in 1985(75).

seems appropriate to provide a brief overviewof the key factors or mechanisms that havebeen identified as precedent to the initiation ofovulatory cycles.Endocrine and Uterine Factors Involvedin the Postpartum Interval to FirstOvulation

Malven (45) defined the problem of thepostp artum period as requiring recovery offunction after pregnancy and parturition ofboth the brain-pituitary-ovarian system and thegenital tract. F uncti onal recovery of thesemajor components of the reproductive systemoccurs simultaneously and there are obviousinteractions. The important endocrine anduterine mechanisms wilt only be summarized

here, since detailed reviews have been publishedelsewhere (27, 35, 42, 68).Prior to the first ovulation and the sub-sequent reestablishment of normal fertility inthe postpartum period, the brain-pituitary-ovarian axis undergoes an ordered sequence ofrecovery events (45). This sequence includes: 1)recovery from pregnancy state (exposure tohigh concentrations of estrogen, progesteroneand other placental hormones), 2) escape fromsuckling (or lactation)-induced inhibition ofgonadotro pins, 3) initiation of luteal develop-ment with or without preceding ovulation, and4) occurrence of estrus with ovulation andluteal life span sufficient to foster pregnancy.As reviewed previously (45, 54, 67, 68), pitui-tary LH content and responsiveness to gonado-

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770 BUTLER AND SMITH

tropin-releasing hormone (GnRH) increaserapidly from their nadir at parturition. Re-covery seems nearly complete by d 10 inmilked dairy cows as in suckled beef cows (52).Plasma concentrations of FSH increase withinthe first 3 to 5 d postpartum, while recovery ofa normal LH secretion patter n is delayed unti l d10 to 20 (42, 43). Basal plasma LH concen-trations rise as a more fr equent episodic patte rnof pulsatile LH release develops. This pulsepatter n appears to be the primary stimulus forovarian follicular development leading to firstovulation, since exogenous GnRH repeatedlyadmin iste red at 2-h intervals for 48 h to an-estrous dairy cows results in pulsatile LHpatterns, a preovulatory type LH surge, ovula-tion, and normal luteal functi on (42). The earlyestabl ishmen t of pulsatile GnR H and LH releaserequisite for first ovulat ion is inhib ited bysuckling (42) and also is directly related to thepresence of the uterus during the puerperium(67).

Involution of the uterus following par-turition affects not only the recovery of LHsecretion but possibly also another importantaspect of ovarian activi ty, luteal lifespan. Anearly sign that gonadotropin secretion hasrecovered in postpartum dairy cows is anincrease in progesterone secretion. This initialluteal progesterone activity often precedes thefirst detect ed estrus and often is short, lasting 4to 12 d, rather than 13 to 20 d as followingnormal ovulation (80). The abbreviated lutealphase has been suggested to result from ex-

aggerated release of p rost aglandin F2 a duringuterine involution (38).R e l a t i o n s h i p o f M i l k P r o d u c t i o nt o P o s t p a r t u m I n t e r v a l t o O v u l a t i o n

The onset of o vulat ory estrous cycles occursduring the first few weeks of lactation. Thepost partu m interval to first ovulation rangesfrom 17 to 42 d as summarized from a num berof studies (Table 2)~ The interval to first ovula-tio n has been related positively to milk yield insome studies, but this has not been a consistentfinding. In our own experience, the correlationbetween milk yield and days to first ovulationbecomes significant only after the period(40 d) when most cows have already ovulated(7). The variation among cows and experi-mental studies suggests that other factors inadd iti on to milk yield per se are involved indetermining the interval to first ovulation. Ascited in Table 2, one well-known factor thatdelays ovulation and estrus is the sucklingstimulus. However, because dairy cows areusually milked rather than being suckled theeffects of nursing on first ovulation will not beconsidered here.

The metabolic demand of high milk yield indairy cows is another factor that should beconsidered with regard to its possible effect onpostpartum ovarian activity. During earlylactation the rate of increase in milk productionexceeds that of feed intake. The general re-lationship between dietary energy intake andenergy utilization is defined as energy balance

TABLE 2. Effects of milking or suckling during lactation on the postpartum interval (PP1) in days to firstovulation or estrus in dairy cows.Days to ovulation (0) or estrus (E)

Milked Suckled PPI r e l a t e d t o milk yield R e f e r e n c e17 (0) -~. = 4336 kg (69)18 (0) Positive (77)21 (0) 39 (0) (8)30 (E) 73 (E) (72)36 (0) X = 7386 kg, Pos. 1 (7)42 (0) 88 (0) (42)21 (0) X = 8260 kg, NS (21)33 (0) Est..X = 7618, NS (31)19 (0) .X = 4600 kg (13)

i Positive.Journal of Dairy Science Vol. 72, No. 3, 1989


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- 2 0 - 1 5 - 1 0 - 5 0A V G . E N ER G Y B A L A N C E ( M c a l / d )Figure 2. Relationship between average energybalance and average milk product ion dur ing the f i r s t20 d of lac ta t ion in dai ry cows [By permission f romButler et al . (7)] .

A V G . E N E R G Y B A L A N C E ( M c a l / d )Figure 3. Relationship between average energybalance dur ing the f i r s t 20 d of lac ta t ion and numberof days to ovula t ion in dai ry cows [By permissionf rom But ler e t a l . (7 ) ] .

a n d is d e s c r i b e d b y t h e f o ll o w i n g e q u a t i o n :d a i l y e n e r g y b a l a n c e = N E 1 ( c o n s u m e d ) - N E 1( r e q u ir e d ) . W h e r e t h e N E 1 r e q u i r e m e n t i n c l u de sb o t h m a i n t e n a n c e a n d p r o d u c t i o n c o m p o n e n t s .C o m p u t a t i o n o f e n e r g y b a l a n c e r e f le c t s t h em e t a b o l i c s t a t u s o f t h e c o w m o r e a c c u r a t e l yt h a n d o e s s i m p l y m e a s u r i n g m i l k y i e ld . D u r in ge a r l y l a c t a t io n t h e d e f i c i e n c y i n d i e t a r y e n e r g yi n t a k e r e l a t i v e t o t h e e n e r g y u t i l i z e d f o r m i l kp r o d u c t i o n r e s u l t s i n n e g a t i v e e n e r g y b a l a n c e ,a n d t h i s c o n d i t i o n m a y p e r s is t f o r s e v e ra l w e e k s( 9 , 7 0 ) . N e g a t i v e e n e r g y b a l a n c e u s u a l l y r e a c h e si t s m a x i m u m d u r i n g w k 1 t o 2 o f l a c t a t i o n a n dr e c o v e r s a t a v a r i a b l e r a t e . T h e d i r e c t r e l a-t i o n s h i p ( r = - . 8 0 ) b e t w e e n m i l k y i e l d a n de n e r g y b a l a n c e i s s h o w n i n F i g u r e 2.

N e g a t i v e e n e r g y b a l a n c e i n l a c t a t i n g d a i r yc o w s i s s im i l a r m e t a b o l i c a l l y to o t h e r s i t u a t i o n so f u n d e r n u t r i t i o n . I n a d e q u a t e n u t r i t i o n e x -a c e r b a t e s s u c k l i n g - i n d u c e d a n e s t r u s i n b e e fc o w s ( 1 6 , 2 6 , 8 0 ) . I n d a i r y c o w s , n e g a t i v ee n e r g y b a l a n c e is d i r e c t l y r e l a t e d t o t h e p o s t -p a r t u m i n t e r v a l t o f i r s t o v u l a t i o n ( F i g u r e 3 ).T h i s r e l a t i o n s h i p b e c a m e s i g n if i c an t b y 2 0 dp o s t p a r t u m , w h e r e a s m o r e r e c e n t s t u d i e si n d i c a t e d t h a t t h e r e l a t io n s h i p b e c o m e s e s t ab -l i s h e d w i t h i n t h e f i r st 2 w k o f l a c t a t i o n ( 1 , 1 3 ) .

R e c o v e r y o r i m p r o v e m e n t i n e n e r g y b a l a n c ef r o m i t s m o s t n e g a t i v e s t a t e a t th e o n s e t o fl a c t a t i o n t o w a r d a p o s it i ve s t a te m a y p r o v i d e ani m p o r t a n t s ig n a l f o r i n i t i a t i o n o f o v a r i a na c t i v i t y . A s d e s c r i b e d i n o u r p r e v i o u s s t u d y ,f i r s t o v u l a t i o n o c c u r r e d , o n a v e r a g e , a p p r o x i -

m a t e l y 1 0 d a ft e r m a x i m a l n e g a t i ve e n e r g yb a l a n c e a n d n e a r p e a k l a c t a t i o n ( 7 ) . A t o v u l a -t i o n , e n e r g y b a l a n c e w a s s t i l l n e g a t i v e , b u t i n a l lc a s e s i t w a s r e t u r n i n g t o w a r d b a l a n c e . T h es i g n i fi c a n t c o r r e l a t i o n o f d a y s t o o v u l a t i o n w i t hc u m u l a t i v e o r a v e ra g e e n e r g y b a l a n c e , b u t n o tw i t h d a i l y e n e r g y b a la n c e n e a r o v u l a ti o n ,s u g g es t s t h a t b o t h m a g n i t u d e o f n e g a t iv e e n e r g yb a l a n c e a n d r e c o v e r y r a t e a r e i m p o r t a n t .R e l a t i n g n e g a t i v e e n e r g y b a l a n c e t o t h e p o s t -p a r t u m i n te r v a l t o o v u l a t i o n m o r e d i r e c t l yq u a n t i f i e s a n d e x t e n d s e a r li e r r e p o r t s th a ts h o w e d t h e n e g a t i v e e f f e c t s o f m i l k y i e l d( 4 7 , 8 8 ; r e f e r e n c e s i n T a b l e 2 ) .D a i r y c o w s i n n e g a t i v e e n e r g y b a l a n c e l o s eb o d y w e i g h t w h e n b o d y r e s e r ve s a r e m o b i l i z e da s e n e r g y r e s o u r c e s to s u p p o r t l a c t a t i o n . B o d yw e i g h t l o s se s r e l a t i n g t o i n c r e a s e d d a y s t o f i r s to v u l a t i o n h a v e a p p r o a c h e d o r r e a c h e d s ig n i f i-c a n c e i n p r e v i o u s s t u d i e s ( 3 1 , 7 0 , 7 7 ) . B e c a u s ei n d i v i d u a l co w s r e s p o n d t o n e g a ti v e e n e r g yb a l a n c e b y d i f f e r e n t c o m b i n a t i o n s o f i n c r e a s e df e e d i n t a k e a n d m o b i l i z a t i o n o f b o d y r e s e rv e s ,n e i t h e r c h a n g es i n b o d y w e i g h t n o r m i l k y ie l da r e a s s e n s i t i v e a s e n e r g y b a l a n c e i n p r e d i c t i n gt h e i m p a c t o n d a y s t o o v u l a t io n . E x a m p l e s o ft h e s e r e l a t io n s h i p s i n tw o n o r m a l H o l s t e i n c o w sa r e p r e s e n t e d i n F i g u r e s 4 a n d 5 . C o w 1 6 8 8p r o d u c e d 7 1 3 1 k g in a 3 0 5 - d l a c t a t i o n . A l -t h o u g h i n c r e a s e s in f e e d e n e r g y i n t a k e la g g e db e h i n d t h e e n e r g y d e m a n d s o f i n c r ea s i n g m i l ky i e l d , b o d y w e i g h t w a s m a i n t a i n e d r e f l e c t in g

Journa l of Da iry Science Vol. 72, No. 3, 1989


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F i g u r e 4 . Re l a t i o n s h i p s a m o n g m i l k y i e ld , d i g e st i b le e n e r g y ( D E ) i n ta k e , b o d y w e i g h t , a n d e n e r g y b a l a n c e(EB) dur ing ea r ly lac ta t ion fo r cow 1688 . Es t rus fo l lowed by ovu la t ion occur red on d 22 , 43 , and 62 a s in -d ica ted by th e a r rows and th i s cow conc e ived to f i rs t insemina t ion (d 62) .

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Figure 5 . R e la t ionsh ips am ong m i lk y ie ld , d iges t ib le ene rgy (DE) in take , bod y we igh t , and ene rgy ba lance( E B) d u r i n g e a r l y l a c t a t i o n f o r c o w 2 6 . F i r s t o v u l a t i o n ( a n d e st r us ) o c c u r r e d o n d 7 6 . Co n c e p t i o n d i d n o t o c c u rfo l low ing insem ina t ions dur ing e s t rus on d 76 o r 96 .Journa l o f Da i ry Sc ience Vol . 72, No . 3 , 1989


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SYMPOSIUM : INTERACTIONS OF NUTRITION AND REPRODUCTION 773s i m u l t a n e o u s m o b i l i z a t i o n o f b o d y r e se r ve s a n di n c r e a s i n g g u t c o n t e n t s a s a p p e t i t e i n c r e a s e d .E n e r g y b a l a n c e r e m a i n e d n e g a ti v e f o r 5 w k o fl a c t a t i o n . F i r s t o v u l a t i o n (a n d e s t r u s ) o c c u r r e do n d 2 2 w h e n t h e e x t e n t o f n e g a ti v e e n e r g yb a l a n c e w a s d i m i n i s h i n g . A s a n o t h e r e x a m p l e ,c o w 2 6 ( F i g u r e 5 ) p r o d u c e d m o r e m i l k ( 9 3 8 6k g / 3 0 5 d o f l a c t a t i o n ) a nd l o s t 9 5 k g o f b o d yw e i g h t b e f o r e e n e r g y b a l a n c e n e a r e d z e r o a t w k1 2 o f l a c t a t i o n . T h e l o n g e r d u r a t i o n o f n e g a t i v ee n e r g y b a l a n c e a p p e a r e d t o r e s u l t f r o m t h e l a c ko f s u s t a i n e d i n c r e a s e s i n f e e d i n t a k e , b u t n oc l in i c al s y m p t o m s o f k e t o si s o r o t h e r h e a l t hp r o b l e m s w e r e o b s e r v e d . E s tr u s a n d o v u l a t i o nd i d n o t o c c u r u n t i l d 7 6 o f l a c t a t i o n . A s in t h ep r e v i o u s e x a m p l e , o v u l a t i o n o c c u r r e d w h e ne n e r g y b a l a n c e w a s s t il l n e g a ti v e b u t w a s a p -p r o a c h i n g z e r o .

C o l l e c t i v e l y , t h e f o r e g o i n g i n f o r m a t i o n s u g -g e s ts th a t d u r i n g t h e m e t a b o l i c d e m a n d s o f h ig hm i l k y i e l d in e a r l y la c t a t i o n , t h e c o n s e q u e n tn e g a t iv e e n e r g y b a l a n c e d e t e r m i n e s t h e t i m i n go f r e s u m p t i o n o f o v u l a t o r y o v a r i a n c yc l es .I n t u r n , t h e t i m i n g o f f i r st o v u l a t i o n d e t e r m i n e sa n d l i m i t s th e n u m b e r o f e s t ro u s c y c l es w h i c hw i l l o c c u r b e f o r e t h e r e c o m m e n d e d p e r i o d o fi n s e m i n a t i o n . W e s u gg e st t h a t t h e d e m o n s t r a b l en e g a t i v e e f f e c t s o f h i g h m i l k y i e l d o n c o n -c e p t i o n r a t e m o s t l i k e l y r e s u lt t h r o u g h d e l a y so r f a i l u r e o f e a r l y r e s u m p t i o n o f o v u l a t i o n i nt h e p o s t p a r t u m p e r i o d , t h e r e b y a l lo w i n g f e w e ro v u l a t o r y c y c l e s b e f o r e i n s e m i n a t i o n a n dt h u s r e s u l t i n g i n l o w e r f e r t i l i t y . S u p p o r t f o r s u cha r e l a t i o n s h i p c o m e s f r o m a s t u d y i n w h i c hc u m u l a t i v e m i l k y i e l d d u r i n g t h e f i r s t 3 w k o fl a c t a t i o n w a s r e la t e d t o s u b s e q u e n t p r e g n a n c yr a t e s a f t e r b r e e d i n g ( 1 4 ) . W e c o n c l u d e t h a t t h en e g a t i v e e f f e c t s o f l a c t a t i o n o n f e r t i l i t y a re re -l a t e d t o t h e e x t e n t o f n e g a t iv e e n e r g y b a l a n c ea n d b e c o m e m a n i f e s t t h r o u g h t i m i n g o f f ir s to v u l a t i o n .Relat ionsh ips o f A va i lab le Body Reservesand Cond i t ion w i th SubsequentReproduct ive Performance inLactat ing Cows.

A n i m p o r t a n t c o m p o n e n t o f e n e rg y b al a n ced u r i n g t h e p u e r p e r i u m i s t h e m o b i l i z a t i o n o fb o d y r e s e r v e s . I t s e e m s a p p r o p r i a t e t o c o n s i d e rt h e p o s s i b l e e f f e c t s o f d i f f e r e n c e s i n b o d yc o n d i t i o n a n d r e s er v e s a t t h e t i m e o f p a r t u r i -t i o n o n a d a i r y c o w ' s a b i l i t y t o a c h i e v e h i g h m i l ky i e ld a n d m a i n t ai n r e c o m m e n d e d 1 2 - t o 1 3 -m o

c a l vi n g i n t e r v a ls . I n o t h e r w o r d s , m i g h t t h er e s p o n s e s t o n e g a t i v e e n e r g y b a l a n c e b e a f -f e c t e d b y d i f f e r e n c e s i n t h e b o d y r e s e r v e sa v a i l a b l e i n o b e s e v e r s u s l e a n c o w s ?

A s e r io u s c o n s e q u e n c e o f o v e r f e e d i n g d a i r yc a t t l e is w h a t h a s b e c o m e k n o w n a s t h e " f a tc o w s y n d r o m e " . T h i s d i s o r d e r w a s f i r s t d e -s c r i b e d i n h e r d s w h e r e c o w s w e r e g r o s s l y o v e r f e dd u r i n g l a te l a c t a t i o n a n d t h e d r y p e r i o d a n di s c h a r a c t e r i z e d b y a n i n c r e a s e d o c c u r r e n c e o fm e t a b o l i c , i n f e c t i o u s , d i g e s t iv e , a n d r e p r o -d u c t i v e d i s o r d e r s ( 4 9 , 5 0 ). D u r i n g a 4 - m op e r i o d a 6 0 0 c o w h e r d f e d c o r n s il a ge a n db r e w e r s g r a in s a d l i b t h r o u g h o u t t h e l a c t a t i o na n d d r y p e r i o d s e x p e r i e n c e d a 3 8% i n c i d e n c e o fk e t o s i s (5 0 ) . S i x t y - t w o p e r c e n t o f t h e c o w s t h a tc a l v e d d u r i n g t h i s p e r i o d r e t a i n e d f e t a l m e m -b r a n e s . M e t r i ti s , s l o w u t e r i n e i n v o l u t i o n , a n dd e l a y e d r e b r e e d i n g a r e c o m m o n l y r e p o r t e dc l i n i c a l f i n d i n g s i n o v e r t l y o b e s e c o w s ( 4 4 ) .C o w s w i t h m e t a b o l i c d i s o r d e r s c o m m o n l ya s s o c i a te d w i t h f a t c o w s y n d r o m e ( e. g. , m i l kf e v e r ) a r e a t r i s k to d e v e l o p s u b s e q u e n t r e -p r o d u c t i v e d i s o r d e r s ( 1 9 ) w h i c h d i r e c t l y a n di n d i r e c t l y r e s u l t in r e d u c e d r e p r o d u c t i v ep e r f o r m a n c e ( 1 2 , 2 3 , 6 5 ) . T h e o b v i o u s c o n -c l u s i o n i s t h a t o b e s i t y a t t h e t i m e o f c a lv i n gs h o u l d b e a v o i d e d ( 4 4 ) .

T h e c o n s e q u e n c e s o f f a t c o w s y n d r o m e a r es e v e r e, a n d t h e g r o s s l y o b e s e c o w i s e a s i l yr e c o g n i z e d . A l t h o u g h m a n y p r o d u c e r s a r et a k i n g p r e c a u t i o n s t o l i m i t i n t a k e s o f c on -c e n t r a t e s a n d c o r n s i la g e d u r i n g t h e l a t e la c -t a t i o n a n d d r y p e r i o d s t o p r e v e n t c l a s s i c al " f a tc o w " p r o b l e m s o r to p r o m o t e b o d y c o n d i t i o nl o s s , t h i s s i t u a t i o n h a s r a i s e d tw o q u e s t i o n s : 1 )Is m o d e r a t e o v e r c o n d i t i o n i n g , n o t r e s u lt i n g ino b e s e c o w s a n d c l a s s ic a l f a t c o w s y n d r o m e ,s u f f i c i e n t t o c a u s e a n i n c r e a s e d i n c i d e n c e o fh e a l t h d i s o r d e r s a n d i m p a i r e d r e p r o d u c t i v ep e r f o r m a n c e ? 2 ) W i l l t h e p r o m o t i o n o f d r yp e r i o d b o d y c o n d i t i o n l os s a f f e c t s u b s e q u e n tm i l k p r o d u c t i o n , h e a l t h , o r r e p r o d u c t i o n ?

A n e x p e r i m e n t d e s i gn e d t o a n s w e r t h e s eq u e s t i o n s h a s r e c e n t l y b e e n c o n d u c t e d ( 7 4 ) .H i g h p r o d u c i n g , m a t u r e c o w s w e r e a s s i g n e d t oo n e o f t h r e e t r e a t m e n t g r o u p s a t 1 2 0 d p o s t -p a r t u m . C o n t r o l s w e r e f e d a h a y c r o p s i l a g e( H C S , 5 4 % ) a n d c o r n s i l a g e ( C S , 3 6 % ) r a t i o nw i t h a n e n e r g y d e n s i t y o f 1 .5 M c a l / k g a n d ap r o t e i n c o n t e n t o f 1 3 % d u r i n g l a t e l a c t a t i o n .B o d y c o n d i t i o n s c o r e s ( 8 9 ) r a n gi n g f r o m 1 . 0( t h i n ) t o 5 . 8 ( o b e s e ) w e r e a s s ig n e d w e e k l y , a n d

Journ al of D airy Science Vol. 72, No. 3, 1989


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7 7 4 B U T L E R A N D S M I THT A B L E 3 . T h e i n c i d e nc e o f h e a l t h a n d r e p r o d u c ti v ed i s o r d e r s i n c o n t r o l c o w s ( C) , o v e r c o n d i t i o n e d c o w s( O C) , a n d o v e r c o n d i t i o n e d c o w s i n w h i c h b o d yc o n d i t i o n l o s s w a s i n d u c e d b y f e e d r e s t r i c t i o n d u r i n gt h e d r y p e r i o d ( O CR) .

G r o u pDisorde r C OC OC RN o . s a m p l e s 4 4 2 2 3 0Milk f eve r 4 4 2Ke tos is 3 3 5Re t a i n e d p l a c e n t a 1 4 7 1 1Me tr i t i s 6 7 9Cys t ic ova r ie s 5 6 9

f e e d i nt a k e s w e r e a d j u s t e d t o m a i n t a i n b o d yc o n d i t i o n s c o r e s i n t h e r a n g e 3 . 8 t o 4 .2 . T h eo t h e r t w o g r o u p s w e r e o v e r c o n d i t i o n e d ( b o d yc o n d i t i o n s c o r e s i n t h e r a n g e 4 . 5 t o 5 . 2 ) b yf e e d i n g a ra t i o n t o s u p p o r t 2 7 k g o f m i l k ( H C S ,2 2 % ; C S , 4 2 % . 1 . 6 M c a l / k g ; 1 5 % C P ) d u r i n gl a t e l a c t a t i o n . D u r i n g t h e e n t i r e d r y p e r i o d t h ec o n t r o l g r o u p ( C ) a n d o n e g r o u p o f t h e o v e r -c o n d i t i o n e d c o w s ( O C ) w e r e f e d a r a t i o n t om a i n t a i n c o n d i t i o n s c o r e s ( H C S , 5 0 % ; C S ; 5 0 % ;1 . 4 M c a l / k g ; 9 .2 % C P ; 1 0 k g D M / d ) . T h es e c o n d o v e r c o n d i t i o n e d g r o u p ( O C R ) w a s f e d ar a t i o n t o p r o m o t e b o d y c o n d i t i o n t os s u n t i l2 w k p r e p a r t u m ( H C S , 1 0 0 % ; 1 .0 M c a l / k g ; 1 3 %C P ; 4 . 1 k g D M / d ) . T h i s r a t i o n p r o v i d e d a p -

p r o x i m a t e l y 5 0 , 5 5 , a n d 1 0 0% o f N R C r e-q u i r e m e n t s f o r e n e r g y , p r o t e i n , a n d m i n e r a l s .B e g i n n i n g a t 2 w k p r i o r t o c a l v i ng , O C R c o w sw e r e f e d t h e d r y c o w r a t i o n p r e v i o u s l y d e -s c r i b e d f o r C a n d O C c o w s . A f t e r c a l v in g , a l lc o w s w e r e f e d a d l ib ( H C S 2 5 % ; C S 4 4 % ; 1 . 6M c a l / k g ; 1 6 % C P ) . T h i s p r o t o c o l w a s r e p e a t e dd u r i n g e a c h o f t w o s u c c e s s iv e l a c ta t i o n s .

B o d y c o n d i t i o n s c o re s f o r C , O C , a n d O C Rg r o u p s a v e r a g e d 3 . 9 -+ . 0 6 , 4 . 7 -+ . 0 9 a n d 4 . 3 -+. 0 8 . B o d y w e i g h t s a v e r a g e d 6 8 6 +- 6 , 7 5 4 + 8a n d 7 1 1 -+ 7 k g , r e s p e c t i v e l y , a t 1 t o 2 w k p r i o rt o c a l vi n g . S c o r e s a n d w e i g h t s w e r e h i g h e r i nO C t h a n i n C a n d O C R ( P < . 0 1 ) . M i l k p r o -d u c t i o n ( 8 0 0 0 + 1 6 2 k g i n e x p e r i m e n t a l l a c-t a t i o n 1 a n d 8 0 6 3 -+ 2 2 8 k g i n l a c t a t i o n 2 ) a n db u t t e r f a t p e r c e n t ( 3 .7 + .1 ) d i d n o t d i f f e r a cr o s st r e a t m e n t g r ou p s . T h e i n c i d e n c e o f h e a l th a n dr e p r o d u c t i v e d i s o r d e r s d i d n o t d i f fe r a c r o sst r e a t m e n t g r o u p s ( T a b l e 3 , P > . 1 0 ) . L i k e w is e ,r e p r o d u c t i v e p e r f o r m a n c e ( w i t h th e e x c e p t i o no f d a y s t o f ir s t o b s e r v e d e s t ru s ) d i d n o t d i f f e rs i g n i f i c a n t l y ( T a b l e 4 ) .

T h e s e d a t a s u g g e s t t h a t o v e r f e e d i n g a n dm o d e r a t e o v e r c o n d i t i o n i n g a t c a lv in g t o t h ee x t e n t o b s e r v e d i n t h is s t u d y ( c o n d i t i o n s c o r e s4 + t o 5 - o n t h e W i l d m a n s c a le ) d o n o t a d -v e r se l y a f fe c t r e p r o d u c t i v e p e r f o r m a n c e . I nc o n t r a s t , o t h e r s r e p o r t e d t h a t o v e r f e e d i n gd u r i n g t h e l a t e l a c t a t i o n , d r y p e r i o d s , o r b o t hi n c r e a s e d t h e i n c i d e n c e o f d i s e a se ( 8 3 ), r e t a i n e dp l a c e n t a ( 1 7 ) , m e t r i t i s ( 1 7 , 8 8 ) , a n d c y s t i c

T A B L E 4 . Re p r o d u c t i v e p e r f o r m a n c e ~ i n c o n t r o l c o w s ( C), o v e r c o n d i t i o n e d c o w s (O C) , a n d o v e r c o n d i t i o n e dc o w s i n w h i c h b o d y c o n d i t i o n l os s w a s i n d u c e d b y f e e d r e s t ri c t i o n d u r i n g t h e d r y p e r i o d ( O CR ) .

G r o u pV a r i a b le C O C O CRNo. samples 43 21 29Day s to f irs t ovu la t io n 2 30 +- 3 32 4 31 4Day s to f irs t obse rved estrus 49 _+ 4 a 51 6 a 36 5 bDay s to f irs t service 71 +- 2 70 3 65 3Fi r s t se rv ice con cep t ion r a te , % 56 48 45Service s per co nc ep tion 2.3 -+ .3 2.2 .4 2.1 .3Pregna ncy r a te , % 100 86 93Da ys op en 103 +- 8 88 -+ 10 94 9

a b e n . . . .M a s wi th in row s wi th d i f f e re n t supe r sc r ip t s d i f f e r (P< .05 ) .1M ean -+ SEM .2 D e t e r m i n e d b y m i l k p r o g e s t e r o n e a n a ly si s o f s a m p l e s o b t a i n e d t w i c e w e e k l y f r o m p a r t u r i t i o n t o c o n f i r m a -t i o n o f p r e g n a n c y b y r e c t a l p a l p a t i o n .

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SYMPOSIUM: INTERACTIONS OF NUTRI TION AND REPRODUCT ION 775

ovaries (44) and lengthened the postpartumintervals to first estrus, ovulation (17, 88), andconception (51). The reasons for these dif-ferences remain to be determined, but couldrelate to types of rations fed, degree of over-conditioning at calving, prepartum adjustmen tto the lactating cow ration, or postpartumnutritional status and body condition loss.Nevertheless, the results of the Cornell,ex-periments strongly suggest that neither moderateoverco nditi oning at calving nor energy re-striction to promote body condition loss inoverconditioned cows during the dry periodadversely affect milk production, health, orreproductive performance in high producingcows when rations are carefully monitored andadjusted as needed to maximize DM intake andminimize body condition loss during earlylactation.Relationship of Postpartum Weightand Body Con di t ion Loss toReproductive Performance

The severity of postpartum negative energybalance and the delay in the init iati on ofnormal postpartum reproductive cyclicity (7) isassociated with body weight and body condi-tion loss. One might predict impaired repro-ductive performance in cows that lose excessiveamounts of body condition during early lac-tation. The existance of such a relationship

would make body condition scoring a usefultool for relating suboptimal reproductiveperformance to inadequate nutrit ion in earlylactation.

Cows in t he Cornell expe rimen t cited wereregrouped based on body condition loss (BCL)during the first 5 wk of lactation: minor(BCL1), 1.0 uni t lost. Reproducti ve per-formance was impaired in cows exhibitingsevere body condition loss (Table 5). Theincidence of metritis was higher in BCL2 andBCL 3 (22 and 47%; respectively) than in BCL a(6%), but this did not account for the dif-ferences observed in reproductive performance.Performance in cows treated for metritisdid no t differ significantly from t hat in otherCOWS.Excessive mobilization of body reserves hasbeen associated with postpartum fatty in-filtration of the liver and reduced reproductiveperformance in high yielding dairy cows. In aprevious study, 69 of 109 cows were classifiedas having fatty livers [>20% fat by volume;(58)] but did not exhibit clinical signs of fatcow syndrome (59). However, cows with fattyliver showed significant alterations of liverfunction and calved subsequently at intervalsaveraging 33 d longer than for cows withoutfatty livers. The delay in conc eptio n was due to

TABLE 5. The relationship between body condition loss during the first 5 wk postpartum and reproductiveperformance. 1

Body condition loss group 2Variable BCL~ BCL2 BCL3No. samples 17 64 12Days to first ovulation 3 27 2a 31 2a 42 5bDays to first observed estrus 48 6 ab 41 3a 62 7bDays to first service 68 4 a 67 2 a 79 5 bFirst service conception rate, % 65 a 53 a 17bServices per conception 1.8 .4 2.3 .2 2.3 .4Pregnancy rate, % 94 95 100

a'bMeans within rows with different superscripts differ (P


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776 B U T L E R A N D S M I T H

a d e l a y i n t h e o n s e t o f e s t r o u s c y c l e a c t i v i t ya f t e r c a l v in g a n d a r e d u c e d c o n c e p t i o n r a t e .

S t u d i e s o n t h e p a t h o g e n e s i s o f f a t t y l iv e rs u g g e s t t h a t i t i s p a r t o f a g e n e r a l i z e d f a tm o b i l i z a t i o n s y n d r o m e t h a t o c c u r s d u r i n g e a r l yl a c t a t i o n i n h i g h y i e l d i n g co w s . T h e m o b i l i z a -t i o n o f t h e s e r e s e r v e s i s r e f l e c t e d i n a lo s s o fb o d y c o n d i t i o n a n d b o d y w e i g h t . H ig h m i l ky i e l d p o t e n t i a l a n d f a t n e s s a t c a l v in g ( 2 3 , 6 1 ,6 2 ) a p p e a r t o b e p r e d i s p o s i n g f a c to r s . C o m m o nf e a t u r e s o f t h e s y n d r o m e a r e o v e r f e e d in g d u ri n gt h e d r y p e r i o d o r d e p r e s s i o n o f D M i n t a k e a n dn e g a t i v e e n e r g y b a l a n c e i n e a r l y l a c t a t i o n ( 6 0 ,8 2 ) .

T h e m e c h a n i s m b y w h i c h f a t t y i n f i lt r a t i o no f t h e l iv e r a f f e c t s r e p r o d u c t i v e p e r f o r m a n c er e m a i n s t o b e d e f i n e d . F a t t y l iv e r c o u l d s im p l yb e a s y m p t o m o f t h e n e g a t i v e e n e r g y b a l a n c et h a t h a s b e e n d e m o n s t r a t e d t o i m p a i r r e p r o d u c -t iv e p e r f o r m a n c e . T h e r e s u lt s o f t h e s t u d y ( 7 4 )p r e s e n t e d i n t h e p r e v i o u s p a r a g ra p h s u p p o r tt h i s v i e w , s i n c e c o w s i n B C L 3 s u f f e r e d m o r es e v e r e n e g a ti v e e n e r g y b a l a n c e ( P < . 0 5 ) a n dd e m o n s t r a t e d h i g h e r li v er f a t c o n t e n t s t h a n t h eo t h e r g r o u p s ( 3 5 . 9 + 2 . 9 v s . 2 4 . 8 + 2 . 5 % ,P < . 0 1 ) .Mechanisms for Ef fects of Negat iveEnergy Balance on Days toO v u l a t i o n

T h e i n t e r a c t i o n s o f t h e m o s t i m p o r t a n tf a c t o r s a f f e c t i n g o v a r i a n a c t i v i t y in p o s t p a r t u mc o w s a r e s u m m a r i z e d in F i g u r e 6 [ a d o p t e df r o m ( 8 0 ) ] . A s d e s c r i b e d p r e v i o u s ly , th er e e s t a b l i s h m e n t o f a n o r m a l L H p u l s e p a t t e r n i st h e k e y f a c t o r r e s p o n s i b l e f o r o v ar i a n f o l l ic u l a rd e v e l o p m e n t a n d t h e i n i ti a t i o n o f p o s t p a r t u mo v a r i a n c y c l i c i t y . S u c k l i n g a n d r e l a t e d s t i m u l io r u n d e r n u t r i t i o n h a ve b e e n i d e n t i fi e d a s t h em o s t i m p o r t a n t n e g a ti v e i n f lu e n c e s o n L H p u l s es e c r e t i o n . D a i r y c o w s i n e a r l y l a c t a t i o n r e p -r e s e n t a s i t u a t i o n o f u n d e r n u t r i t i o n d u e t oh ig h m i l k y i e l d s c o u p l e d w i t h i n a d e q u a t e f e e di n t a k e a n d t h e c o n s e q u e n t n e g a ti v e e n e r g yb a l a n c e . I n s u c k l e d l a c t a t i n g b e e f c ow s , u n -d e r n u t r i t i o n r e d u c e s b o t h F S H a n d L H c o n -c e n t r a t i o n s f o r e x t e n d e d p e r i o d s ( 8 0 ), w h e r e a si n m i l k e d d a i r y c o w s , o n l y L H s e e m s t o b ed e f i c i e n t a f t e r 5 t o 1 0 d p o s t p a r t u m ( 4 2 , 6 6 ,6 8 , 8 0 ) .

T h e d i r e c t e f f e c t s o f n e g a t i v e e n e r g y b a l a n c eo n L H p u l s e p a t t e r n s h a v e b e e n a s s e s s e d d u r i n g

p e r i o d s o f e n e r g y r e s t r i c t i o n ( 3 4 ) . H e i f e r s w e r eo v a r i e c t o m i z e d a n d f e d b e l o w r e q u i r e m e n t su n t i l b o d y w e i g h t s w e r e r e d u c e d 2 0% . I n t h ea b s e n c e o f o v a r i a n s t e r o i d s , e n e r g y r e s t r i c t i o nr e s u l te d i n r e d u c e d L H p u l s e f r e q u e n c y b u th i g h e r p u l s e a m p l i t u d e . T h e s e n s i t i v i t y t on e g a t i v e f e e d b a c k e f f e c t s o f e s t r a d i o l w a se n h a n c e d , b u t t h i s w a s s e c o n d a r y to d i r e c t e f-f e c t s o n L H p u l s e s e c r e t i o n .

A n u m b e r o f o t h e r s t u d i e s h a v e p r o v i d e di n f o r m a t i o n o n t h e r e l a t io n s h i p o f d i e t a r ye n e r g y a v a i l a b i l i t y t o L H s e c r e t i o n . In s u c k l e db e e f c o w s , c h r o n i c u n d e r n u t r i t i o n i n h i b i t e d L Hr e l e a s e i n r e s p o n s e t o c a l f r e m o v a l w i t h r e d u c -t i o n i n b o t h L H p u l s e fr e q u e n c y a n d p e a kc o n c e n t r a t i o n s ( 8 6) . T h e L H r e s p o n s e to c a l fr e m o v a l w a s s h o w n t o b e b l o c k e d b y a c u t ei n d u c e d h y p o g l y c e m i a (6 4 ) . T h e a u t h o r ss u g g e s te d t h a t t h e i m p a i r e d L H r e s p o n s e w a sd u e t o l o w e r g l u c o s e a v a i l a b i l i t y . H o w e v e r , L Hp a t t e r n s r e m a i n e d a l t e re d d u r i n g t h e e n t i r e ti m ew h e n i n s u li n r e m a i n e d l o w w h i c h e x t e n d e db e y o n d t h e p e r i o d o f h y p o g l y c e m i a . T h i ss u g g e s t s t h a t i n s u l in c o n c e n t r a t i o n s r a t h e r t h a ng l u c o s e m a y h a v e d i r e c t l y a f f e c t e d L H s e c r e-t i o n . T h i s h y p o t h e s i s g a in s s u p p o r t f r o m as t u d y i n n o n l a c t a t i n g h e i f e r s i n w h i c h t h es u p p r e s s i o n o f i n s u l i n d u r i n g f a s t in g a n d a b r u p ti n c re a s e s d u r i n g r e f e e d in g w e re t e m p o r a l l yl i n k e d t o o n g o i n g L H s e c r e t i o n (4 8 ) . T h ep r e s e n c e o f i n s u l i n r e c e p t o r s l o c a t e d i n t h e

SUCKLING MILKING

PRL SECRETION p LH PULSATILITY FSH SECRETION

o _ [E S ~ I O L

Figure 6 . In terac t ions among ex ternal and endo-crine factors affecting ovarian activ ity in pos tpart umcows [Adapted f rom Terqui e t a l . (80) ] . - -EB =negative energy balance, PGF2a = prostaglandinF2a , PR L = Prolactin.

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SYMPOSIUM: INTERACTIONS OF NUTRITION AND REPRODUCTION 77 7m e d i a n e m i n e n c e ( 8 5) o f t h e h y p o t h a l a m u ssugges t s a reg u l a to ry ro l e fo r i n su l in i n t hem e t a b o l i s m o f g l u c o s e i n t h i s n e u r a l t i s s u e ,w h i c h c o u l d , in t u r n , m o d u l a t e h y p o t h a l a m i cG n R H o u t p u t . M e d i a n e m i n e n c e a n d p i t u i t a r yt i s s u e s f r o m f a s t e d r a t s p r e f e r e n t i a l l y m e -t a b o l i z e d k e t o n e s , r a t h e r t h a n g l u c o s e ( 3 0 ) ,a l l o w i n g t h e p o s s i b i l it y t h a t a s w i t c h f r o mg l u c o s e t o k e t o n e u t i l i z a t i o n d u r i n g i n a d e q u a t ee n e r g y i n t a k e m a y s i g n a l d e c r e a s e d g o n a d o -t r o p i n a c t i v i t y .

A m o r e l i k e l y l i n k t h a n i n s u l i n b e t w e e nn e g a t i v e e n e r g y b a l a n c e a n d d e c r e a s e d L Hs e c r e t i o n i n v o l v e s a c t i v a t i o n o f n e u r o e n d o c r i n eo p i o i d p a t h w a y s . O n e o f t h e m o s t s ig n i fi c a ntp h y s i o l o g i ca l f u n c t i o n s o f n e u r a l o p i o i d p e p -t i d e s i s th e i r a s s o c i a t i o n w i t h f e e d i n g b e h a v i o r( 3 , 1 0 ) . A c t i v a t i o n o f o p i o i d p a t h w a y s s t i m u -l a t e s f e e d i n g , a n d b l o c k i n g o p i o i d r e c e p t o r sw i t h t h e a n t a g o n i s t , n a l o x o n e , i n h i b i t s f e e din t ake . A d i rec t re l a t i onsh ip w i th nega t i vee n e r g y b a l a n c e w a s s u g g e s t e d w h e n D y e r e t a l .( 1 5 ) r e p o r t e d i m p a i r m e n t o f L H se c r e t io n inf a s t i n g o v a r i e c t o m i z e d r a t s a n d t h a t t h i sc o u l d b e p r e v e n t e d w i t h n a l o x o n e p r e t r e a t -m e n t . T h e e f f e c t o f f a s ti n g w a s a r e d u c t i o n i nL H p u l s e a m p l i t u d e . I n t h e s a m e s t u d y , f a s t i n ga l s o i m p a i r e d L H r e l e a s e d u r i n g n e u r a l e x -c i t a t i o n o f t h e v e n t r a l n o r a d r e n e r g i c t r a c t i n t h eb r a i n s t e m . H e r e a g a i n n a l o x o n e p r e v e n t e d t h ei n h i b i t o r y e f f e c t s o f f a s t i n g . T h e s e i m p o r t a n tr e s u l t s a n d o t h e r s d e s c r i b i n g t h e o p i o i d m e d i a -t i o n o f L H s e c r e t i o n ( 4 , 1 1 , 3 7, 4 6 ) s u p p o r ta n d f u r t h e r d e s c ri b e t h e n e u r a l p a t h w a y s f o ro p i o i d i n h i b i t i o n o f G n R H r e l ea s e . A s r e v i e w e db y B i c k n e l l ( 5 ) , e x c i t a t o r y n o r a d r e n e r g i cn e u r o n s o r i g i n a t i n g i n t h e b r a i n s t e m s y n a p s e o nG n R H p r o d u c i n g n e u r o n s l o c a t e d i n t h e a n -t e r i o r h y p o t h a l a m u s a n d p r e o p t i c a r e a . P r e -s y n a p t i c o p i o i d i n h i b i t i o n o f t h e s e n o r a d r e n e r g i cn e u r o n s a r is e s b o t h f r o m o u t s i d e t h e h y p o -t h a l a m u s ( e n k e p h a li n p a t h w a y ) o r f r o m w i th i nt h e b a s a l h y p o t h a l a m u s n e a r t h e a r c u a t en u c l e u s ( 3 - e n d o r p h i n p a t h w a y ) . T h e r e i sadd i t i ona l ev idence s ugges t i ng t ha t t he /3-e n d o r p h i n p a t h w a y m a y a l s o d i r e c t l y i m p i n g eo n t h e G n R H n e u r o n s a s t h e y t e r m i n a t e n e a rt h e p i t u i t a r y p o r t a l v e s s el s i n t h e m e d i a ne m i n e n c e .A l t h o u g h t h e e v i d e n c e s u g g e s t i n g a n e u r a ls it e o f a c t i o n f o r i n h i b i t o r y e f f e c t s o f o p i o i d so n G n R H m e d i a t e d L H s e c r e t io n is w e ll -d o c u m e n t e d , a c t io n s w i th i n t h e a n t e r i o r

p i t u i t a r y g l a n d m u s t a l s o b e c o n s i d e r e d . O p i a t ep e p t i d e s , a c t i n g t h r o u g h s p e c i f ic o p i a t e - b i n d i n gs i te s , e x e r t d i r e c t i n h i b i t o r y e f f e c t s o n a n t e r i o rp i t u i t a r y L H r e l e a se i n v i t r o ( 6 ) . T h e m o s tp r e v a l e n t e n d o g e n o u s o p i o i d , 3 - e n d o r p h i n , i sr e le a s ed f r o m t h e h y p o t h a l a m u s i n t o t h ep i t u i t a r y p o r t a l s y s t e m ( 3 9 ) a n d c o u l d t h e r e b yr e a c h p i t u i t a r y s i te s o f L H p r o d u c t i o n . P e r h a p s ,j u s t a s i m p o r t a n t l y , j 3 - e nd o r p h in i s p r o d u c e dw i t h i n a n t e r i o r p i t u i t a r y g l a n d c o r t i c o t r o p h sf r o m p r o - o p i o c o r t i n , t h e s a m e p r e c u r s o r a s f o ra d r e n o c o r t i c o t r o p i n ( 1 8 ). I n c u b a t i o n o f d is -p e r s e d a n t e r i o r p i t u i t a r y c e l l s w i t h c o r t i c o -t r o p i n - r e l e a s i n g h o r m o n e ( C R H ) i n h i b i t e d b a s a lL H r e l e a s e , a n e f f e c t t h a t w a s r e v e r s e d b ya d d i t i o n o f a n o p i a t e a n t a g o n i st ( 6 ). T h e e f f e c to f C R H w a s p r e s u m a b l y t h r o u g h r e l e a s e o fo p i o i d p e p t i d e s i n d i c a t in g t h a t t h e s e m a y e x e r ta p a r a c r i n e i n h i b i t o r y a c t i o n o n g o n a d o t r o p h s .T h e r e l e v a n c e o f t h e s e p o s s i b l e d i r e c t e f f e c t s o fo p i o i d s t o p i t u i t a r y L H r e l e a s e d u r i n g n e g a t i v ee n e r g y b a l a n c e c a n o n l y b e p o s t u l a t e d a t t h ep r e s e n t t i m e . E n h a n c e d t 3 - e n d o r p h i n r e l e a s ef r o m t h e h y p o t h a l a m u s o r a n t e r i o r p i t u i ta r ym a y b e r e l a te d t o t h e s t i m u l a t i o n o f a p p e t i tea n d d i e t a r y i n t a k e t h a t n o r m a l l y o c c u r s i n e a r l yl a c t a t i o n a n d m a y , i n t u r n , e x e r t i n h i b i t o r ye f f e c t s o n h y p o t h a l a m i c G n R H r e l e a s e , p i t u i -t a r y L H r e l e a s e , o r b o t h .A p r e l i m i n a r y m o d e l t o i n v e s t i g a t e f u r t h e rt h e i n v o l v e m e n t o f o p i o i d s o n p u l s a t i l e L Hs e c r e t i o n d u r i n g n e g a t i v e e n e r g y b a l a n c e h a sb e e n d e v e l o p e d ( C a n f i e l d a n d g u t l e r , u n -p u b l i s h e d ) . O v a r i e c t o m i z e d e w e s w e r e p l a c e do n a n e n e r g y r e s tr i c te d d i e t i n O c t o b e r a n dw i t h i n 8 w k h a d l o s t 2 0 % o f t h e i r b o d y w e i g h t .B l o o d s a m p l e s w e r e c o l l e c t e d t h r o u g h i n -d w e l l i n g v a s c u la r c a n n u l a e f o r 1 6 h a t 1 2 - m i ni n t e r v a l s t o c h a r a c t e r i z e L H p u l s e p a t t e r n s .D u r i n g t h e l a s t 8 h o f f r e q u e n t s a m p l i n g , f i v e o ft h e e w e s w e r e i n f u s e d w i t h n a l o x o n e ( a n o p i o i dan t ag on i s t , 25 mg i. v. a t t he beg inn ing o f eachh ) w h i l e t he o the r f i ve ew es rece ived sa l i ne .U p o n c o m p l e t i o n o f th e f r e q u e n t s a m p l i n g , a lle w e s w e r e i n j e c te d w i t h G n R H ( 1 0 n g / k g ) , a n db l o o d s a m p l i n g c o n t i n u e d a t 3 0 - m i n i n t e r v a l s f o ra n a d d i t i o n a l 4 h . I n s e v e ra l e w e s n a l o x o n e t r e a t -m e n t r e s u l t e d i n i m m e d i a t e i n c r e m e n t s i n L Hp u ls e a m p l i t u d e w i t h o u t c h a n g i n g p u ls e fr e q u e n -c y a n d a v e ra g e b a sa l p l a s m a L H c o n c e n t r a t i o n si n c r e a s e d a b o u t 2 5 t o 3 0% ( F i g u r e 7 ) . P u l s ep a t t e r n s w e r e s t a b l e a n d u n c h a n g e d d u r i n g t h es a m e p e r i o d i n c o n t r o l a n i m a l s . P i t u i t a r y L H

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7 7 8

" i

BUTLER AND SMITH

B 1 0 7 5 cNALOXONE

7 0

i - ml 0

0 I i ! i I i I i I I I I I I0 I~ II O tO 111 1 4 10

Figure 7. Plasma LH concen trations in an ovarie ctom ized ewe (B1075c) du ring negative energy balance.Nalo xone was injected h ourly ( i .v .) beginning at 8 h, which increased LH pulse am plitude and basal LH con-centra t ions.

r e l e a se in r e s p o n s e t o G n R H w a s e q u a l i n b o t hn a l o x o n e a n d s a l i n e t r e a t e d g r o u p s. T h e s ep r e l i m i n a r y r e s u l ts i n d i c a t e t h a t n e u r a l o p i o i dp a t h w a y s m o d u l a t e L H p u l s e s e c r e t i o n d u r i n gn e g a t i v e e n e r g y b a l a n c e . B e c a u s e L H p u l s ea m p l i t u d e w a s i nc r e a s ed b y n a l o x o n e , w h i l e th ep i t u i t a r y r e sp o n s e t o G n R H w a s u n c h a n g e d , t h ep r i m a r y e f f e c t o f o p i o i d i n h i b i t i o n w o u l da p p e a r t o b e o n t h e m a g n i t u d e o f e n d o g e n o u sG n R H p u ls e s b e i ng p r o d u c e d . T h e m a n n e r o rs i te o f a c t i o n f o r s u c h m o d u l a t i o n o f t h e G n R Hp u l se g e n e ra t i n g s y s t e m c a n n o t b e d e t e r m i n e df r o m t h e s e e x p e r i m e n t s , b u t a g re e s w i t h p r e-v i o u s r e s u l t s in f a s t i n g r a t s ( 1 5 ) . F u t u r e e x p e r i -m e n t s a r e p l a n n e d f o r e a r l y l a c t a t i n g c o w s t oi n v e s t i g a t e t h e r o l e o f o p i o i d s i n t h e e f f e c t s o fn e g a ti v e e n e r g y b a l a n c e o n p a t t e r n s o f L Hs e c r e t i o n a n d d a y s t o f i r s t o v u l a t i o n . A r e c e n ts t u d y h a s s h o w n t h a t o p i o i d s a r e i n v o l v e d i ns u c k l i n g - i n d u c e d a n e s t r o u s i n b e e f c o w s ( 8 7 ) .

Metabol ic and Endocr ine Interre lat ionshipsin the Pos tpar tum Cow : A W ork ing Mode lT h e e a r l y p o s t p a r t u m p e r i o d in l a c t a ti n g

d a i r y c o w s w a s c h a r a c t e r i z e d i n p r e v i o u ss e c t i o n s a s i n v o l vi n g m a n y m e t a b o l i c a d j u s t -m e n t s a n d t h e i r i n t e r p l a y w i t h c o m p l e x e n -d o c r i n e m e c h a n i s m s r e l a t e d t o n o r m a l o v a ri a na c t i v i t y . N e g a t i v e e n e r g y b a l a n c e r e s u l t s f r o m at e m p o r a r y i m b a l a nc e b e t w e e n d i e t a ry in t a k ea n d t h e e n e r g y d e m a n d s o f i n c re a s in g m i lkp r o d u c t i o n ( 70 ). A c c o m m o d a t i o n t o t h es em e t a b o l i c d e m a n d s is a c c o m p l i s h e d b y c o m -b i n a t i o n s o f i n c r e a s e s i n d i e t a r y i n t a k e a n dm o b i l i z a t i o n o f b o d y e n e r g y re s e rv e s , w h i c hd i f fe r a m o n g i n d i v id u a l co w s . T o u n d e r s t a n dt h e p o s s i b l e ne g a ti v e i m p a c t s o f l a c t a t i o n o nr e p r o d u c t i v e p e r f o r m a n c e , i t is n e c e s s a r y t oc o n s i d e r t h e a s s o c i a t i o n s a m o n g m e t a b o l i cf a c t o r s i n c l u d i n g in c r e a s ed a p p e t i t e a n d m a r k e di n c r e a s e s i n g l u c o s e u t i l i z a t i o n , i n t e r a c t i o n o f

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SYMPOSIUM: INTERACTIONS OF NUTRITION AND REPRODUCTION 779

s t i m u l i r e s p o n s i b l e f o r i n c r e a s e d m i l k p r o -d u c t i o n , a n d t h e m e c h a n i s m s n e c e s s a r y f o ro v a r i a n a c t i v i t y t h a t m i g h t b e s u b j e c t t o i n -h i b i t i o n . S o m e o f t h e s e q u e l a e to n e g a ti v ee n e r g y b a l a n c e a n d i n c r e a s e d f e e d i n g b e h a v i o rr e l a t i n g t o m e t a b o l i t e s , o p i o i d s , a n d t h e L Hp u l s e s y s t e m a r e d i a g r a m m e d i n F i g u r e 8 . T h i ss i m p l e d i a g r a m i s i n t e n d e d t o e m p h a s i z e t h em e t a b o l i c o r o p i o i d f a c t o r s m o s t e a s i l y r e l a t e dt o L H p u l s a t il i ty a n d d o e s n o t a t t e m p t t oe x p l ai n t h e c o m p l e x i t ie s o r i m p o r t a n t m e c h -a n i s m s r e g u l a t i n g a p p e t i t e a n d f e e d i n g b e h a v i o rin ca t t le (2 , 3 ) .

D u r i n g n e g a t i v e e n e r g y b a l a n c e i n e a r l yl ac t a t i on , t he rap id i nc reases i n u t i l i za t i on o fg l u c o s e f o r m i l k l a c t o s e p r o d u c t i o n r e s u l t s i nl o w e r p l a s m a c o n c e n t r a t i o n s o f b o t h g l u c o s ea n d i n s u l i n a s c o m p a r e d w i t h t h a t i n l a t e r s t a g e so f l a c ta t i o n ( 2 9 , 7 3 ). A l t h o u g h t h e c o m b i n e de f f e c t s o f l o w e r g l u c o s e a n d i n s u l in m a y p l a y am i n o r r o l e i n s t i m u l a t i n g f e e d i n g b e h a v i o r ( 2 ) ,t h e r e l a t i v e la c k o f i n s u li n w o u l d e n h a n c el i po ly s i s i n ad ipose t i s sues , t he reby fu r the rinc reas ing appe t i t e v i a i nc reased ava i l ab i l i t y o ff r e e f a t t y a c i d s f o r h y p o t h a l a m i c o x i d a t i o n( 3 6 ) . T h e i n c r e a s e d f e e d c o n s u m p t i o n f r o mt h e s e e f f e c t s a n d o t h e r a d d i t iv e s t i m u l i i n e a r l yl a c t a t i o n w o u l d l i k e l y b e a s s o c i a t e d w i t hinc reased re l ease o f / 3 -endo rph in w i th in t heh y p o t h a l a m o - h y p o p h y s e a l u n i t ( 2 , 3, 1 0 ).E l e v a t e d / 3 - e n d o r p h i n w o u l d b e e x p e c t e d t oi n h i b i t t h e G aa R H p ul s e s y s t e m ( F i g u r e 8 ) . A t

t h e s a m e t i m e , t h e G n R H s y s t e m a n d , h e n c e ,L H p u l se p a t t e r n s m a y b e d e p r e ss e d d i r e c t l y b yl o w i n s u l i n a n d s e c o n d a r i l y b y t h e i n c r e a s e dp r o d u c t i o n a n d u t i l iz a t i o n o f k e t o n e s a s a c o n -s e q u e n c e o f m o b i l i z a t i o n o f b o d y a d ip o s er e s e r v e s ( 3 0 , 8 5 ) . A l t h o u g h t h e r e l a t i v e i m -p o r t a n c e o f t h e v a r i o u s i n h i b i t o r y i n p u t sr e m a i n t o b e e st a b l is h e d , t h e e n d r e s u l t w o u l db e i n t e r f e r e n c e w i t h t h e d e v e l o p m e n t o fp o s t p a r t u m L H p u l se p a tt e r n s . I n n o n l a c t a t i n gca t t l e , nega t i ve en e rgy ba l ance a l t e r s pu l sa t i l eL H r e l e a s e a n d L H p u l s e s a r e d e p r e s s e d f u r t h e rb e c a u s e o f e n h a n c e d s e n s i t i v it y t o n e g a ti v ef e e d b a c k e f f e c t s o f o v a r i a n s t e r o id s ( 3 4 ) .

E n d o g e n o u s o p i o i d s r e l a t e n o t o n l y t od i e t a r y i n t a k e d u r i n g n e g a t iv e e n e r g y b a l a n c eb u t a l so t o t h e r e le a s e o f s e v er a l h o r m o n e si m p o r t a n t t o t h e i n d u c t i o n a n d m a i n t e n a n c e o fl a c t a t io n . M i l k in g i n d u c e s r e le a s e o f p r o l a c t i n( 4 0 ) , a d r e n o c o r t i c o t r o p i n [ as m e a s u r e d b yg l u c o c o r t i c o i d s (4 1 ) ] a n d o x y t o c i n (2 4 ) , a n dt h e r e le a s e o f e a c h involves o p i o i d s ( 5 , 18, 5 5 ) .W e s u g g e s t t h a t t h e s e l a c t a t i o n s t i m u l i , c o u p l e dw i t h i n c re a s e d a d r e n o c o r t i c o t r o p i n i n r e s p o n s et o h y p o g l y c e m i a a n d i n cr e a s ed f e e d i n g b e h a v i o rin sp i red by t he ene rgy de f i c i t , a re a l l supe r -i m p o s e d d u r i n g t h e e a r l y l a c t a t i o n p e r i o d t oy i e l d a s i t u a t i o n i n w h i c h n e u r o e n d o c r i n eo p i o i d m e c h a n i s m s d o m i n a t e p u ls a ti le G n R Ha n d L H s ec r e ti o n . O u r s p e c u l a t i o n o n t h el in k a ge b e t w e e n t h e s e a n d o t h e r m e c h a n i s m s ina m o d e l f o r t h e p o s t p a r t u m c o w is d i a g r a m m e d

NEGATIVE NERGY ALANCE/ . 'xHYPOGLYCEMIA ,,- =,

_ ~ +KET(~ES B-ENDORPHIN

GNRHPULSATILITY+4OVARIANSTEROIDS LHPULSATILITYID

Figure 8. Interactions am ong metabolic andopioid factors related to negative energy balance,feeding behavior and the system generating LH pulses.B-ENDORPHIN = ~-endorphin, GNRH = gonado-tropin-releasing horm one.

NEGATIVE NERGYBALANCE+ / , \ ,HYPOGLYCEMIA FEEDING

~ x ~ . H + ~ A CT H+ B-ENDORPHIN I +, Y , O I N S O L I N E M I A . .. . 4 - -

( ~ GNRHPULSATILITY NEI - / \ + Nill+ PULSATILITY FSH SECRETIO

OVARIANACTIVITY

Figure 9. M od el for th e relationships of negativeenergy balance to gonadotropin secretion in post-partum lactating cows. AC TH = adrenocorticotropin,B-ENDO RPHIN = ~-endorphin, CRH = cort icotropin-releasing hormone, GN RH = gonadotropin-releasinghorm one, NE = norepinephrine.Journal of Dairy Science Vo l. 72, No. 3, 1989


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i n F i g u r e 9 . W e s u g g e s t t h a t n e g a t i v e e n e r g yb a l a n c e o p e r a t i n g t h r o u g h a n u m b e r o f i n-t e r r e l a t e d p a t h w a y s i n v o l v i n g o p i o i d s a n di n s u l i n i s l a r g e l y r e s p o n s i b l e f o r r e g u l a t i n g t h eL H p u l s e p a t t e r n s t h a t s e e m c r u c i a l f o r t h eo n s e t a n d t i m i n g o f p o s t p a r t u m o v a r i an f u n c -t i o n .

A l t h o u g h w e h y p o t h e s iz e t h a t t h e m e c h -a n i s m s l i n k i n g n e g a t i v e e n e r g y b a l a n c e t o L Hp u l s a t il i ty a r e m o s t i m p o r t a n t f o r g o v e r n i n gp o s t p a r t u m o v a r ia n a c t iv i t y , a n a d d i t i o n a la s p e c t o f o v a r ia n r e g u l a t i o n h a s r e c e n t l y b e e ne m e r g i n g . I n s u li n h a s b e e n s h o w n t o e x e r ta c t i o n s o n o v a r i a n t i s su e s t h a t a r e v e r y s im i l a rt o t h o s e o f p i t u i ta r y g o n a d o t r o p i n s ( 5 7) . T h e s ea c t i o n s i n c l u d e d i re c t e f f e c t s o n s t e r o i d o g e n i ce n z y m e s , m o d u l a t i o n o f g o n a d o t r o p i n r e c e p t o rn u m b e r , s y n e rg i s m w i t h o t h e r g o n a d o t r o p i n s ,a n d n o n s p e c i f i c e n h a n c e m e n t o f c e ll v i a b il i ty .B a s e d o n t h e d i v e r s i t y o f t h e s e a c t i o n s w ep o s t u l a t e t h a t l o w e r i n s u l i n a v a i l a b i li t y d u r i n ge a r l y l a c t a t i o n m a y r e n d e r o v a r i a n f o l li c l e s l es sr e s p o n s iv e to a n y o n g o i n g g o n a d o t r o p i n s t i m u -l a t io n . G o n a d o t r o p i c e f f e c t s o f in s u li n o nf o l li c u la r d e v e l o p m e n t h a v e b e e n i n d i c a t e d b ye x p e r i m e n t s i n e n e r g y r e s t r i c t e d h e if e r s ( 2 8 ,4 8 ) .I n s u m m a r y , p o s t p a r t u m r e p r o d u c t i v e f u n c -t i o n i n d a i r y c a t t l e s ee m s d i r e c t ly d e p e n d e n t o nt h e a v a i l a b i li t y o f n u t r i e n t e n e r g y r e l a t i v e t o i tsu t i l i z a t i o n f o r l a c t a t i o n . N e g a t i v e e n e r g yb a l a n c e p r i m a r i l y a p p e a r s t o i n t e r f e r e w i t h t h ea b i l it y o f th e h y p o t h a l a m o - h y p o p h y s e a l a x is t od e v e l o p t h e p u l s a t i l e L H p a t t e r n n e c e s s a r y f o rf o s t e r i n g o v a r i a n f o l l i c u l a r d e v e l o p m e n t a n do v u l a t i o n . S e c o n d a r i l y t h e e n e r g y d e f i c i t a n dl o w i n s u li n c o n c e n t r a t i o n s d u r i n g t hi s p e r i o dm a y l i m i t t h e r e s p o n s i v e n e s s o f t h e o v a r y t og o n a d o t r o p i n s t i m u l a t io n . T h e i n te r v a l t o fi rs to v u l a t i o n in t h e p o s t p a r t u m p e r i o d d e p e n d su p o n r e c o v e r y o f t h e n o r m a l f u n c t i o n s o f t h eb r a i n - p i t u i t a r y - o v a r i a n a x i s a n d t h e g e n i t a lt r a c t. S u b s e q u e n t f e r t i l i t y is c o n v e y e d f r o m a ne a r ly o n s e t o f f ir s t o v u l a t i o n a nd c o m p l e t i o n o fm u l t i p l e c y c le s b e f o r e i n s e m i n a t i o n .

RE F ERENCES1 Al l r ich , R. D . , K . A . Be rghorn , a nd C. H . Nol le r .

1 9 8 7 . I n f l u e n c e o f e n e r g y b a l a n c e o n o v a r i a na c t i v i t y a n d e s t ro u s b e h a v i o r i n p o s t p a r t u m d a i r ycow s. J . Da iry Sci. 70(Supp l. 1) : 184. (Ab str .)2 Ba i le , C. A . , and M. A . De l la -Fe ra . 1981 . Na ture o fh u n g e r a n d s a t i e t y c o n t r o l s y s t e m s in ru m i n a n t s . J .

Da i ry Sc i . 64 :1140 .3 Baile , C. A., C. L. McLaughlin, and M. Della-Fera .1 9 8 6 . Ro l e o f c h o l e c y s t e k i n i n a n d o p i o i d p e p t i d e si n c o n t r o l o f f o o d i n t a k e . Ph y s i ol . Re v . 6 6 : 1 7 2 .4 Bhan ot , R. , and M. Wilk inson . 1984 . Th e in -h i b i t o r y e f f e c t o f o p i a t e s o n g o n a d o t r o p h i ns e c r e t i o n i s d e p e n d e n t u p o n g o n a d a l s t e r o i d s .J . E n d o c r i n o l . 1 0 2 : 1 3 3 .5 Bickne l l , R . J . 1985 . En dogen ous op io id pep t idesa n d h y p o t h a l a m i c n e u r o e n d o c r i n e n e u r o n e s . J .E n d o c r i n o l . 1 0 7 : 4 3 7 .6 Blank , M. S . , A . Fab br i , K . J . Ca r t , and M. L .D u f a u . 1 9 8 6 . I n h i b i t i o n o f l u t e i n iz i n g h o r m o n er e l e a s e b y m o r p h i n e a n d e n d o g e n o u s o p i a t e s i nc u l t u r e d p i t u i t a r y c e ll s. E n d o c r i n o l o g y 1 1 8 : 2 0 9 7 .7 But le r , W. R. , R. W. Eve re t t , and C. E . Coppock .1 9 8 1 . T h e r e l a t io n s h i p s b e t w e e n e n e r g y b a l an c e ,m i l k p r o d u c t i o n a n d o v u l a t i o n in p o s t p a r t u mHols te in cows . J . Anim. Sc i . 53 :742 .8 Carruthers , T. D., and H. D. Hafs. 1980. Sucklinga n d f o u r - t i m e s d a i l y m i l k i n g : i n f l u e n c e o n o v u l a -t i o n , e s t ru s a n d s e r u m l u t e i n i z in g h o r m o n e , g l u -c o c o r t i c o i d s a n d p r o l a c t i n i n p o s t p a r t u m H o l s te i n s.J . Anim. Sc i . 50 :919 .9 Co ppoc k , C. E . , C . H . Nol le r , and S . A . Wolfe .1 9 7 4 . E f f e c t o f f o r a g e - c o n c e n t r a t e ra t i o in c o m -p l e t e f e e d s f e d a d l i b i t u m o n e n e r g y i n t a k e i nr e l a t i o n t o r e q u i r e m e n t s b y d a i r y c o w s . J . D a i r ySc i . 5 7 : 1 3 7 1 .Davis , J . M. , M. T . Lowy, G .K.W. Yim, D . R.Lamb, and P . V . Ma lven . 1983 . Re la t ionsh ipb e t w e e n p l a s m a c o n c e n t r a t i o n s o f i m m u n o r e a c t i v eBe t a - e n d o r p h i n a n d f o o d i n t a k e i n r a ts . Pe p t i d e s4 : 7 9 .D i e z - G u e r ra , F . J . , S . A u g o o d , P . C . E m s o n , a n d R .G. Dyer . 1986 . Morphine inh ib i t s e lec t r ica l lys t i m u l a t e d n o r a d r e n a l i n e r e le a s e f r o m s l i c e s o f r a tm e d i a l p r e o p t i c a re a. N e u r o e n d o c r i n o l o g y 4 3 : 8 9 .12 Do oho o , T . R. , and S . W. Mar t in . 1984 . Disease ,p rod uc t io n and cu l l ing in Hols te in -Fr ie s ian cows .IV . Ef fec ts o f d i sease on p roduc t ion . Prev . Ve t .M e d . 2 : 7 7 5 .Duck e r , M . J ., R . A . Hagge t t , W. J . F ishe r , S . V .M o r a n t , a n d G . A . B l o o m f i e ld . 1 9 8 5 . N u t r i t i o n a n dr e p r o d u c t i v e p e r f o r m a n c e o f d a ir y c a t t le . 1 . T h ee f f e c t o f l e v e l o f f e e d i n g i n l a t e p r e g n a n c y a n da r o u n d t h e t i m e o f i n s e m i n a t i o n o n th e r e p ro -d u c t i v e p e r f o r m a n c e o f f i rs t l a c t a t i o n d a i r y h e i fe r s .A n i t a . P r o d . 4 1 : 1 .14 Duck e r , M. J . , and S . V . Moran t . 1984 . Obse rva -t i o n s o n t h e r e la t i o n s h i p s b e t w e e n t h e n u t r i t i o n ,m i l k y i e l d , l i v e w e i g h t a n d r e p r o d u c t i v e p e r f o r m -a n c e o f d a i r y c o w s . A n i m . P r o d . 3 8 : 9 .15 Dyer , R. G . , S . Mansf ie ld , H . Corbe t , and A .D.P.D e a n . 1 9 8 5 . Fa s t i n g im p a i r s L H s e c r e t i o n i n fe m a l er a t s b y a c t i v a t i n g a n i n h i b i t o r y o p i o i d p a t h w a y . J .E n d o c r i u o l . 1 0 5 : 9 1 .16 Easdon , M . P ., J . M. Chesw or th , M.B.E . Aboul -e la ,and G . D . Hend e r son . 1985 . The e f f ec t o f un-d e r n u t ri t io n o f b e e f c o w s o n b l o o d h o r m o n e a n dm e t a b o l i t e c o n c e n t r a t i o n s postpartum. Re p r o d .N u t r . D e v . 2 5 : 1 1 3 .17 E1-Keraby, F. , a nd E. Schil l ing. 1976. E f f e c t o fo v e r f e e d i n g o f c o w s d u r i n g l a t e l a c t a t i o n o n

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S Y M P O S IU M : I N T E R A C T I O N S O F N U T R I T I O N A N D R E P R O D U C T I O N 7 8 1

r e p r o d u c t i v e p e r f o r m a n c e i n t h e e a r ly p o s t p a r t u mp e r i o d . P a g e 3 6 1 in P r o c . 8 t h A I I n t . C o n g r . A n i t a .R e p r o d . A I .1 8 E i p p e r , B . A . , a n d R . E . M a i n s . 1 9 8 0 . S t r u c t u r ea n d b i o s y n t h e si s o f p r o - A C T H / e n d o r p h i n a n d

r e l a t e d p e p t i d e s . E n d o c r . R e v . 1 : 1 .1 9 E r b , H . N . , R . D . S m i t h , P . A . O l t e n a c u , C . L .G u a r d , R . B . H i l l m a n , P . A . P o w e r s , M . C . S m i t h ,a n d M . E . W h i t e . 1 9 8 5 . P a t h m o d e l o f r e p r o d u c t i v ed i s o r d e r s a n d p e r f o r m a n c e , m i l k f e v e r, m a s t it i s,m i l k y i e l d a n d c u l l i n g i n H o l s t e i n c o w s . J . D a i r yS c i . 6 8 : 3 3 3 7 .2 0 E v e r e t t , R . W . , a n d B . B e a n . 1 9 8 6 . S e m e n f e r -t i l i t y - a n e v a l u a t io n s y s t e m f o r a r ti fi c ia l in s e m i n a -t i o n s i re s , t e c h n i c i a n s , h e r d s , a n d s y s t e m a t i c f i x e de f f e c t s . J. D a i r y S c i . 6 9 : 1 6 3 0 .2 1 F o n s e c a , F . A . , J . H . B r i tt , B . T . M c D a n i e l , J . C .W i l k, a n d A . H . R a k e s . 1 9 8 3 . R e p r o d u c t i v e t r a it so f H o l s t e i n s a n d J e r s e y s . E f f e c t s o f a g e , m i l k y i e l d ,a n d c l i n i c a l a b n o r m a l i t i e s o n i n v o l u t i o n o f c e r v i xa n d u t e r u s , o v u l a t i o n , e s t r o u s c y cl e s , d e t e c t i o n o fe s tr u s , c o n c e p t i o n r a t e , a n d d a y s o p e n . J . D a i r yS c i . 6 6 : 1 1 2 8 .2 2 F o o t e , R . H . 1 9 7 8 . R e p r o d u c t i v e p e r f o r m a n c e a n dp r o b l e m s i n N e w Y o r k D a i r y H e r d s . C o r n e ll U n i v .A g r i c . E x p . S m . S e a r c h 8 : 1 .2 3 F r o n k , T . J ., L . H . S c h u l t z , a n d A . R . H a r d i e .1 9 8 0 . E f f e c t o f d r y p e r i o d o v e r c o n d i t i o n i n g o ns u b s e q u e n t m e t a b o l ic d i s o r d e rs a n d p e r f o r m a n c eo f d a i r y c o w s . J . D a i r y S c i . 6 3 : 1 0 8 0 .2 4 G o r e w i t , R . C . 1 9 7 9 . M e t h o d f o r d e t e r m i n i n go x y t o c i n c o n c e n t r a t i o n s in u n e x t r a c t e d s e ra ;c h a r a c t e r i z a t i o n i n l a c t a ti n g c a t t l e . P r o c . S o c . E x p .B i o l . M e d . 1 6 0 : 8 0 .

2 5 G w a z d a u s k a s , F . C . , W . D . W h i t t ie r , W . E . V i n s o n ,a n d R . E . P e a r s o n . 1 9 8 6 . E v a l u a t i o n o f r e p r o -d u c t i v e e f f i c i e n c y o f d a i r y c a t t l e w i t h e m p h a s i s o nt i m i n g o f b r e e d i n g . J. D a i r y S c i . 6 9 : 2 9 0 .2 6 H a n s e n , P . J. , a n d E . R . H a u s e r . 1 9 8 3 . G e n o t y p e e n v i r o n m e n t a l i n t e r a c t i o n s o n r e p r o d u c t i v e t r a it so f b o v i n e f e m a l e s . I l l . S e a s o n a l v a r i a t i o n i n p o s t -p a r t u m r e p r o d u c t i o n a s in f l u en c e d b y g e n o t y p e ,s u c k l i n g a n d d i e t a r y r e g i m e n . J . A n i m . S c i. 5 6 :1 3 6 2 .2 7 H a n z e n , C . H . 1 9 8 6 . E n d o c r i n e r e g u l a t io n o fp o s t p a r t u m o v a r i a n a c t i v i ty i n c a t t l e : a r e v i e w .R e p r o d . N u t r . D e v . 2 6 : 1 2 1 9 .2 8 H a r r i s o n , L . M . , a n d R . D . R a n d e l . 1 9 8 6 . I n f l u e n c eo f i n s u l i n a n d e n e r g y i n t a k e o n o v u l a t i o n r a t e ,l u t e in i z i n g h o r m o n e a n d p r o g e s t e r o n e in b e e fh e i f e r s . J . A n i t a . S c i. 6 3 : 1 2 2 8 .2 9 H a r t , I . C . , J . A . B i n e s , S . V . M o r a n t , a n d J . L .R i d l e y . 1 9 7 8 . E n d o c r i n e c o n t r o l o f e n e r g y m e -t a b o l i sm i n t h e c o w : C o m p a r i s o n o f t h e l e ve ls o fh o r m o n e s (p r o l a c ti n , g r o w t h h o r m o n e , i n s u li n a n dt h y r o x i n e ) a n d m e t a b o l i t e s i n th e p l a s m a o fh i g h - a n d l o w - y i e l d i n g c a t t l e a t v a r i o u s s t a g e s o fl a c t a ti o n . J . E n d o c r i n o l . 7 7 : 3 3 3 .3 0 H a w k i n s , R . A . a n d J . F . B i e b u y c k . 1 9 7 9 . K e t o n eb o d i e s a r e s e l e c t i v e l y u s e d b y i n d i v i d u a l b r a i nr e g i o n s . S c i e n c e 2 0 5 : 3 2 5 .3 1 H e n r i k s e n , J . , a n d A . M . J e n s e n . 1 9 8 5 . S t u d i e s o nt h e e n d o c r i n e a n d e n v i r o n m e n t a l f a c to r s in f lu -e n c i n g p o s t p a r t u m a c y c l i c it y i n d a ir y c o w s b a s e d

o n p r o g e s t e r o n e p r o f il e s ( p r e li m i n a r y r e su l t s) .E l l e n d o r f f , F . a n d F . E i sa e s se r , e d . Pa g e s 2 2 1 - 2 3 2in E n d o c r i n e c a u s e s o f s e a s o n a l a n d l a c t a ti o n a la n e s t r u s i n f a r m a n i m a l s . M a r t i n u s N i j h o f f P u b l .,B o s t o n , M A .

3 2 H e r m a n H . A . 1 9 5 6 . A g e - f e r t i li t y r e l a t i o n s h i p s i nc a t t l e s e r v i c e d b y a r t i f i c i a l i n s e m i n a t i o n . P a g e5 6 in P r o c . 3 r d I n t . C o n g r . A n i t a . R e p r o d . A I .3 3 H i l le r s , J . K . , P . L . S e n g e r , R . L . D a r l i n g t o n , a n dW . N . F l e m i n g . 1 9 8 4 . E f f e c t s o f p r o d u c t i o n ,s e a s o n , ag e o f c o w , d a y s d r y , a n d d a y s i n m i l k o nc o n c e p t i o n t o f i r s t s e r v ic e i n l a r g e c o m m e r c i a ld a i r y h e r d s . J . D a i r y S c i . 6 7 : 8 6 1 .3 4 I m a k a w a , K . , M . L . D a y , D . D . Z a l e s k y , A . C l u t t e r ,R . J . K i t t o k , a n d J . E . K i n d e r . 1 9 8 7 . E f f e c t s o f1 7 b e t a - e s t r a d i o l a n d d i e t s v a r y i n g i n e n e r g y o ns e c r e t i o n o f l u t e i n i z i n g h o r m o n e i n b e e f h e if e r s . J .A n i t a . S c i . 6 4 : 8 0 5 .3 5 K a r g , H . , a n d E . S c h a l l e n b e r g e r . 1 9 8 2 . F a c t o r sI n f l u e n c i n g F e r t i li t y i n t h e P o s t p a r t u m C o w . C u r t .T o p i c s V e t . M e d . A n i t a . S c i . V o l . 2 0 . M a r t i n u sN i j h o f f P u b l. , B o s t o n , M A .3 6 K a s s e r , T . R . , R . B . S . H a r r i s , a n d R . J . M a r t i n .1 9 8 5 . L e v e l o f s a t i e t y : f a t t y a c i d a n d g l u c o s em e t a b o l i s m i n t h r e e b r a i n s i te s a s s o c i a te d w i t hf e e d i n g . A m . J . P h y s i o l. 2 4 8 : R 4 4 7 .3 7 K e s n e r , J . S ., J . K a u f m a n , R . C . w i l s o n , G . K u r o d a ,a n d E . K n o b i l . 1 9 8 6 . T h e e f f e c t o f m o r p h i n e o nt h e e l e c t r o p h y s i o l o g i c a l a c t i v i t y o f t h e h y p o -t b a l a m i c l u t e i n iz i n g h o r m o n e - r e l e a s i n g h o r m o n ep u l s e g e n e r a t o r i n t h e R h e s u s m o n k e y . N e u r o -e n d o c r i n o l o g y 4 3 : 6 8 6 .

3 8 K i n d a h l , H . , L . E . E d q u i s t , K . L a r s s o n , a n d A .M a l m q u i s t. 1 9 8 2 . I n f l u e n c e o f p r o s t a g l a n d i n s o no v a r i a n f u n c t i o n p o s t p a r t u m . H . K a r g an d E .S c h a l l e n b e r g e r , e d . F a c t o r s i n f l u e n c i n g f e r t i l it y int h e p o s t p a r t u m c o w . G u r r. T o p i c s V e t . M e d . A n i m .S c i . 2 0 : 1 7 3 .3 9 K o e n i g , J . I . , H . Y . M e l t z e r , a n d G . A . G u d e l s k y .1 9 8 6 . M o r p h i n e o r c a p s a i c in a d m i n i s t r a t io n a l t e rst h e s e c r e t io n o f b e t a - e n d o r p h i n i n to t h e h y p o -p h y s i a l p o r t a l v a sc u l a tu r e o f t h e r a t . N e u r o e n -d o c r i n o l o g y 4 3 : 6 1 1 .4 0 K o p r o w s k i , J. A . , a n d H . A . T u c k e r . 1 9 7 3 . S e r u mp r o l a c t i n d u r i n g v a r i o u s p h y s i o l o g i c a l s t a t e s a n d i t sr e l a ti o n s h i p t o m i l k p r o d u c t i o n i n t h e b o v i n e .E n d o c r i n o l o g y 9 2 : 1 4 8 0 .4 1 K o p r o w s k i , J . A . , a n d H . A . T u c k e r . 1 9 7 3 . B o v i n es e r u m g r o w t h h o r m o n e , c o r t i c o i d s a n d i n s u l ind u r i n g l a c t a t i o n . E n d o c r i n o l o g y 9 3 : 6 4 5 .4 2 L a m m i n g , G . E . , A . R . P e t e r s , G . M . R i le y , a n d M .W . F i s h e r. 1 9 8 2 . E n d o c r i n e r e g u l a t i o n o f p o s t -p a r t u m f u n c t i o n . H . K a rg a n d E . S c h a l l e n b e rg e r ,e d . F a c t o r s i n f l u e n c i n g f e r t il i ty i n t h e p o s t -p a r t u m c o w . C u r t . T o p i c s V e t . M e d . A n i t a . S ci .2 0 : 1 4 8 .4 3 L a m m i n g , G . E . , D . C . W a t b e s , a n d A . R . P e te r s .1 9 8 1 . E n d o c r i n e p a t t e r n s o f t h e p o s t - p a r tu m c o w .J . R e p r o d . F e r t i l ( S u p p l . ) 3 0 : 1 5 5 .4 4 M a c C o r m a c k , J . 1 9 8 7 . F a t c o w s y n d r o m e a n d i tsc o m p l i c a t i o n s . V e t . M e d . S m a l l A n i t a . C l i n . 7 3 :1 0 5 7 .4 5 M a l v e n , P . V . 1 9 8 4 . P a t h o p h y s i o l o g y o f th e p u e r -p e r i u m : d e f i n i t i o n o f t h e p r o b l e m . P a g e 1 in P r o c .

J o u r n a l o f D a i ry S c i e n c e V o l . 7 2 , N o . 3 , 1989


16/17


1 0 t h I n t . C o n g r . A n i m . R e p r o d . A I .4 6 M a l v e n , P. V . , D . F . B . B o s s u t , a n d M . A . D i c k m a n .1 9 8 4 . N a l o x o n e a n t a go n i s m o f a n o p i o i d m e c h -a n i s m i n h i b i t o r y t o L H r e l e a s e i n l u t e a l p h a s e e w e s .P a g e 2 7 in P r o c. 1 0 t h I n t. C o n g . A n i m . R e p r o d .A I .4 7 M a r i o n , G . G . , a n d H . T . G i e r . 1 9 6 8 . F a c t o r sa f f e c t i n g b o v i n e o v a r i a n a c t i v i t y a f t e r p a r t u r i t i o n .J . A n i t a . S c i . 2 7 : 1 6 2 1 .4 8 M c C a n n , J . P ., a n d W . H a n s e l . 1 9 8 6 . R e l a t i o n s h i p sb e t w e e n i n s u l in a n d g l u c o s e m e t a b o l i s m a n dp i t u i t a r y - o v a r i a n f u n c t i o n s i n f a s t e d h e i f e r s . B i o l .R e p r o d . 3 4 : 6 3 0 .4 9 M o r r o w , D . A . 1 9 7 6 . T h e f a t c o w s y n d r o m e . J.D a i r y S c i . 5 9 : 1 6 2 5 .5 0 M o r r o w , D . A . , D . H i ll m a n , A . W . D a d e , a n d H .K i t c h e n . 1 9 7 9 . C l i n ic a l i n v e s t i g a t io n o f a d a i r yh e r d w i t h f a t c o w s y n d r o m e . J . A m . V e t. M e d .A s s o c . 1 7 4 : 1 6 1 .

5 1 M o r r o w , D . A . , H . F . T y r r e l l , a n d G . W . T r i m -b e r g e r . 1 9 6 9 . E f f e c t s o f l ib e r al c o n c e n t r a t e f e e d i n go n r e p r o d u c t i o n i n d a i r y c a t t le . J . A m . V e t . M e d .A s s o c . 5 5 : 1 9 4 6 .5 2 M o s s , G . E . , J . R . P a r f e t , C . A . M a r v i n , R . D .A l l r i c h , a n d M . A . D i e k m a n . 1 9 8 5 . P i t u i t a r yc o n c e n t r a t i o n s o f g o n a d o t r o p i n s a n d r e c e p t o r s fo rG n R H i n s u c k l e d b e e f c o w s a t v a r io u s i n te r v a lsa f t e r c a l vi n g . J . A n i t a . S c i . 6 0 : 2 8 5 .5 3 N a s h , J . G . , L . B a l l, a n d J . D . O l s e n . 1 9 8 0 . E f f e c t so n r e p r o d u c ti v e p e r f o r m a n c e o f a d m i n i s tr a t io n o fG n R H t o e a r l y p o s t p a r t u m d a i r y co w s . J . A n i t a .S c i . 5 0 : 1 0 1 7 .

5 4 P e t e rs , A . R . , a n d G . E . L a m m i n g . 1 9 8 4 . E n d o c r i n ec h a n g e s i n t h e p o s t p a r t u m p e r i o d . P a g e 1 7 inP r o c . lO t h I n t C o n g r . A n i m . R e p r o d . A I .5 5 P f e i ff e r , A . , a n d A . H e r z . 1 9 8 4 . E n d o c i n e a c t i o n so f o p i o i d s . H o r m . M e t a b . R e s. 1 6 : 3 8 6 .5 6 P i c k e t t , B . W . , R . C . M a r ti g , a n d W . A . C o w a n .1 9 6 1 . P r e s e r v a t io n o f b o v i n e s p e r m a t o z o a a t - 7 9a n d - 1 9 6 C . J . D a i r y S c i. 4 4 : 2 0 8 9 .5 7 P o r e t s k y , L . , a n d M . F . K a li n , 1 9 8 7 . T h e g o n a d o -t r o p h i c f u n c t i o n o f i ns u li n . E n d o c r . R e v . 8 : 1 3 2 .5 8 R e i d , I . M . 1 9 8 0 . I n c i d e n c e a n d s e v e r i t y o f f a t t yl i v e rs i n d a i r y c o w s . V e t . R e e . 1 0 7 : 2 8 1 .5 9 R e i d , I. M . , a n d R . A . C o l l i n s. 1 9 8 0 . T h e p a t h o l o g yo f p o s t p a r t u r i e n t f a t t y l iv e r i n h i g h - y i e l d i n g d a i r yc o w s . I n v e s t . C l ln . P a t h o l . 3 : 2 3 1 .6 0 R e i d , I . M . , a n d C . J . R o b e r t s . 1 9 8 3 . S u b c l i n i c a lf a t t y l iv e r in d a i r y c o w s - c u r r e n t r e s e a r c h a n df u t u r e p r o s p e c t s . I r . V e t . J . 3 7 : 1 0 4 .6 1 R e i d , I . M . , C . J . R o b e r t s , a n d R . M o n s t o n . 1 9 7 9 .R e d u c e d f e r t i l i t y a s s o c i a t e d w i t h f

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