Milk production and reproductive performance of cows inducedinto lactation and treated with bovine somatotropin

M. Mellado1, E. Nazarre1, L. Olivares1, F. Pastor1 and A. Estrada2

1Department of Nutrition, University Autonoma Agraria Antonio Narro, Saltillo, Mexico2Faculty of Veterinary Medicine and Animal Science, University Autonoma of Sinaloa, Culiacan, Mexico

E-mail: mmellbosq@yahoo.com

Abstract

Milk production and reproductive performance of pluriparous dairy cows was compared for cows whose lactations were

induced by hormonal treatment or followed natural calving. The study was conducted on 179 high-yielding dairy cows in

a large dairy operation in a hot arid environment of northern Mexico, where bovine somatotropin (bST) was routinely

used in all cows. To induce lactation, 98 cows that had previously failed to become pregnant were treated with 500 mg

bST on days 1, 8 and 21. From days 2 to 8, cows were treated with oestradiol cypionate (030 mg/kg live weight (LW)

per day) and progesterone (028 mg/kg LW per day). From days 9 to 15, oestradiol cypionate alone was given. PGF2awas given on day 16. Nothing was administered on days 17 and 18, and 15 mg flumetasone was administered from

days 19 to 21. Lactation was induced successfully in all 98 cows subjected to the hormone treatment. All cows received

500 mg bST every 14 days throughout lactation from 63 ^ 7 days after lactation had started. Cows with induced

lactations produced less ( P , 001) milk per 305-day lactation (9599 ^ 1387 kg) than controls (12 302 ^ 1245 kg).

Proportion of cows pregnant was similar in induced cows and non-treated cows (71 v. 75%). Induction of lactation was

associated with increased numbers of services per pregnancy (58 ^ 40 v. 422 ^ 298; P , 001) compared with

controls; however, impaired reproduction might not necessarily have been related to the hormonal treatment to induce

lactation, but due to the nature of the cows utilized for this treatment group. This protocol can be used on dairy farms

where bST treatment and prolonged steroid administration of dairy cows is legally permitted.

Keywords: dairy cows, lactation curve, lactation duration, milk yield, pregnancy.

IntroductionContinuous selection for increased milk yield in dairy cattlehas resulted in an antagonistic relationship betweenincreasing production and lowered fertility (Pryce et al.,2004). Lowered fertility has become a major reason forinvoluntary culling of dairy cows in intensive systems, par-ticularly in northern Mexico where the extremely high ambi-ent temperatures in this area influence productionefficiency. A high culling rate of high-yielding cows due toreproductive failure reduces profitability as those cows aresold for meat purposes. Replacement cost would bereduced with fewer cows sold for beef purposes and morereplacements available for sale and not to maintain lactatingherd size.

Although hormonal induction of lactation in commercialdairy operations is questionable in a sound managementprogramme, this practice could be used selectively in cowswith fertility problems, but with a high genetic potential formilk production. Protocols for induction of lactation in dairycattle were established three decades ago, using daily injec-tion of oestadiol-17b and progesterone, but outcomes have

been variable; generally milk yields have been erratic andnormally lower than those expected from cows calving nor-mally (Smith and Schanbacher, 1973; Collier et al., 1975;Peel et al., 1978). Data of Magliaro et al. (2004) indicatethat milk production was not different between inducedcows treated with bovine somatotropin (bST) and first-lacta-tion cows whose lactation derived from parturition, and that,despite a short period of bST treatment, the procedure wasprofitable. The current treatments for inducing lactation donot entirely mimic the endocrinological changes associatedwith pregnancy, parturition and lactation (Collier et al.,1975; Chakriyarat et al., 1978). Our study attempted themodify the traditional short hormonal treatment (7 days) toinitiate lactogenesis, with a longer steroid treatment for amore pronounced mammotrophic action of hormones actingduring normal mammogenesis (pregnancy) and lactogen-esis (parturition). Additionally, corticosteroids, and prosta-glandin were used to trigger lactogenesis, and bST wasincluded in the protocol for its ability to stimulate milk produ-cing cell proliferation (Capuco et al., 1989; Knight et al.,1990). Thus, this present study investigated a more com-plex treatment protocol to induce lactation in cattle including

Animal Science 2006, 82: 555559

Q 2006 British Society of Animal Science

ISSN 1357-7298

DOI: 10.1079/ASC200656

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bST treatment throughout lactation. Milk production andreproductive performance were compared between pluripar-ous cows induced to lactation and those whose lactation fol-lowed normal pregnancy and parturition.

Material and methodsThe study was conducted in a large commercial dairy farmin a hot arid environment in northern Mexico, where bSTwas used routinely in all cows. The use of bST is wide-spread in the dairy industry in Mexico, and the current legis-lation allows the use of this protocol to induce lactation incows for milk to be sold for human consumption.

Ninety-eight non-pregnant, dry, healthy pluriparous Holsteincows in good body condition and approximately 575 kg liveweight (LW), which had failed to become pregnant withrepeated services, and had been subjected to bST treat-ment in previous lactations, were induced into lactation by acombination of hormonal treatment. Bovine somatotropin(500 mg i.m., Lactotropinaw Eli Lilly Co., Mexico) was givenon day 1 of treatment. From day 2 to 8, cows received oes-tradiol cypionate (ECPew Pfizer Animal Health MX,030 mg/kg LW per day, s.c.) and progesterone (ProgestynA-Ew Lab. Tornell, Mexico; 028 mg/kg LW per day, s.c.).Bovine somatotropin was again administered on days 8 and15. From day 9 to 15, oestradiol cypionate alone was admi-nistered. Cows were treated with PGF2a (Lutalyse, Pharma-cia and Upjohn, Kalamazoo, MI, 25 mg i.m.) on day 16.Nothing was applied on days 17 and 18. For 3 days con-secutively (19 to 21) cows were treated with flumetasone(Flusolw Lab. Tornell, Mexico, 15 mg i.m.). On day 21 cowsreceived once again bST and were milked.

Eighty-one cows that calved at about the end of thesequence of hormone treatments served as controls. Inorder to avoid a bias in this sample, the criteria used toselect these animals were based on pluriparous cows withfour functional quarters, with no clinical metabolic diseasesand with .9000 kg 305-day lactation yields in their previouslactation. All cows (induced and controls) received 500 mgbST every 14 days, starting at 63 ^ 7 days after calving orinitiation of lactation (induced cows) for the duration oflactation.

All cows were kept as a group and offered a total mixedration composed of 032 lucerne hay, 028 maize silage,022 maize grain, 017 soya-bean meal, and 002 mineralsand vitamins (dry-matter basis). The ration was formulatedto meet the requirement of their current milk production.They were kept in outside lots with metal shades and with afeeding bunk. Food was delivered to cows 10 times duringthe day. Cows were milked three times daily at 8-h intervals.bST was routinely used in previous lactations on all cows ofthis dairy farm, and average 305-days lactation yields in theprevious lactation for induced and controls were 9675 (s.d.1227) and 10 024 (s.d. 1423) kg, respectively. Milk yieldswere recorded every 14 days throughout lactation. Theexperiment lasted until all cows were dried off. The longestlactation was 935 days (17 kg milk in last weighing) for aninduced cow, and 592 days (20 kg milk in last weighing) fora cow with normal calving.

After a voluntary waiting period of 50 days, cows observedto be in oestrus were artificially inseminated. Pregnancywas confirmed by palpation per rectum of the uterine con-tent 50 to 70 days after the last AI date recorded. Dates forcalving, first service after parturition and subsequent ser-vices were recorded. The interval from calving to pregnancy(days open) was recorded.

Lactation yields were analysed as repeated measuresANOVA using the mixed procedure of Statistical AnalysisSystems Institute (SAS, 1996). Proportion of cows pregnantwere evaluated by chi-square analysis (SAS, 1996). Afterlimiting the number of services per conception to cows witha confirmed pregnancy diagnosis, the effect of induction oflactation on the number of services per conception wasevaluated by the bivariate Wilcoxon rank sum test (procnpar1way; SAS, 1996) without adjustment for confounders.Days open for pregnant cows were analysed by the LIFE-TEST procedure of SAS using both strata and time state-ments (SAS, 1996).

ResultsLactations were induced successfully in all non-pregnantcows with reproductive problems. Milk production data ofcows induced into lactation and post-partum lactation arepresented in Table 1. The 305-day yields for cows lactatingafter normal calving were 022 greater ( P , 001) thanthose following induced lactations. In both groups lactationlength was greater than 400 days. Total milk productionwas 013 greater for post-partum lactations compared withinduced lactations and mean daily milk yield during the first305 days of lactation was greater ( P , 001) for inducedlactations than post-partum lactations.

Lactation curves over 350 days of induced and post-par-tum lactations are compared in Figure 1. Cows inducedto lactate took longer to reach peak milk production (125days) but once maximum milk production was reached(34 kg/day) milk yield tended to parallel that of cows lac-tating after normal calving and treated with bST. How-ever, there was a significant interaction ( P , 001)between milk yield and periods, which suggests thatinduced cows did not maintain the same tendency inmilk yields observed in controls throughout lactation.

Data regarding the reproductive performance followinginduced lactation are presented in Table 2. Services perpregnancy in the previous lactation were abnormally high

Table 1 Lactation performance of cows induced into lactation andcows with a post-partum lactation

Lactationfollowingcalving

(no. 81)

Group induced(no. 98)

Mean s.d. Mean s.d.

Yield of 305-days lactation (kg) 12 302 1245 9599** 1387Lactation length (days) 420 133 462 112Total lactation yield (kg) 16 187 4742 14 041 3518Daily milk yield in 305 days (kg) 403 52 314** 45

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in cows whose lactations derived from parturition. Theinduced cows also presented a considerable number ofunsuccessful attempts to become pregnant, before indu-cing them into lactation. No significant effect of inducedlactation was found for average days to first service. How-ever, a higher ( P , 001) number of services per preg-nancy was observed in induced cows than in cows with apost-partum lactation. A very high proportion of inducedand non-induced cows were not detected in oestrusthroughout lactation. Average days open was 58 daysshorter in non-treated cows than in induced cows,although this difference was not significant. Finally, pro-portion of cows pregnant was similar between inducedand non-induced cows and 70 live calves resulted fromthe 98 cows induced successfully to lactate.

DiscussionThe success rate in inducing lactation was 100% but theinduced cows produced 078 of the milk produced by cowswith post-partum lactations. The amount of milk producedby the induced cows as a proportion of that produced bycows after normal calving was similar to that reported byMagliaro et al. (2004) but higher than reports of otherresearchers (Smith and Schanbacher, 1973; Collier et al.,1977; Kensinger et al., 1979), who noted that milk yields ofinduced cows were proportionately 06 to 07 of previousproduction. Moreover, in contrast to previous studies, vari-ation in milk yield among cows induced to lactate wasreduced. The high success rate in inducing lactation and

the acceptable milk yield observed in the present study con-trast with the unsatisfactory milk yields of induced cows withthe traditional 7-to 10-day steroid regime (Collier et al.,1975; Tervit et al., 1980; Davis et al., 1982). To our knowl-edge, this is the first demonstration that cows induced intolactation with the administration of bST in the treatment,and then treated with bST during lactation, reached accep-tably high milk production levels. The longer steroid treat-ment and the use of bST for inducing lactation seem toexplain this response. Sejrsen et al. (1986) and Radcliffet al. (2003) have shown that heifers injected with somato-tropin presented a large increase in mammary parenchymalmass and total mammary cell numbers. Likewise, Sakamotoet al. (2005) suggest that, in addition to its widely acceptedhomeorhetic role in vivo, somatotropin also acts on themammary parenchyma. This mammogenic action ofsomatotropin remains a puzzle, but the effect of exogenousbST most likely involves insulin-like growth factor-1(Forsyth, 1996; Sejrsen et al., 1999).

Mean lactation length of induced cows was over 400 days,with remarkably high levels of milk production (25 kg/day) atthe end of lactation. Despite the fact that both groups ofcows underwent extended lactation, lactation persistencywas remarkably high in both groups. This possibly was dueto the fact that frequent milking causes an increase in mam-mary parenchyma (Henderson et al., 1985), which results ina more persistent lactation curve (Bar-Peled et al., 1995;Knight and Sorensen, 2000). Moreover, administration ofbST may enhance persistency by increasing cell prolifer-ation and turn-over, or by reducing the rate of apoptosis(Capuco et al., 2003), and by maintaining total mammaryparenchyma weight and lactating alveoli (Baldi et al., 2002).

Reproductive performance of cows induced into lactationand cows with a post-partum lactation was poor but, com-pared with previous studies with cows induced to lactate,our results did not reach the extremely low reproductionrates found by others researchers. In the present study 70live calves resulted from 98 cows that were induced suc-cessfully to lactate, whereas others (Collier et al., 1975)obtained only five live calves from 11 induced cows. Evenworse, in another study only two live calves were obtainedfrom 16 induced cows (Harness et al., 1978). Reproductivefailures in these studies have been ascribed to the occur-rence of static, enlarged ovarian follicles (Collier et al.,1975; Erb et al., 1976) and the occurrence of oestrousbehaviour without ovarian structures present (Jordan et al.,

0

10

20

30

40

50

60

0 50 100 150 200 250 300 350Days of lactation

Milk

yie

ld (k

g/day

)

Induced lactation

Postpartum lactation

Figure 1 Milk production curves for induced and control cows.

Points are means ^ s.d.

Table 2 Reproductive parameters of cows induced into lactation and cows with a post-partum lactation

Lactation followingcalving (no. 81)

Group induced(no. 98)

Mean s.d. Mean s.d.

No. of services per cow in previous lactation 533 365 42 30Average days to first service 68 11 71 14Services per pregnancy 422 298 58** 40Cows not observed in oestrus (% and no.) 17 (14/81) 19 (19/98)Days open 206 133 264 172Cows pregnant (% and no.) 75 (61/81) 71 (70/98)

In the induced cows none of the services resulted in pregnancies.

Performance of cows induced into lactation

557

1981). However, normal cyclic activity has been observedby day 27 post treatment in heifers induced to lactate artifi-cially and 92% of these heifers conceived (Sawyer et al.,1986). To circumvent the formation of abnormal ovarian fol-licles in induced cows, Jordan et al. (1981) administeredGnRH, which resulted in proportion of cows pregnant similarto cows with post-partum lactation. Ninety percent con-ception rates in induced cows have also been reported(Peel et al., 1978).

In the present study reproductive management was lessthan ideal, which was reflected in a high failure to conceivefrom regularly spaced services, which led to abnormallyhigh services per pregnancies for both groups of cows. Thisfailure of cows to become pregnant resulted in extremelylong intervals between commencement of lactation and con-ception. Previous studies have also found that interval fromtreatment to induce lactation to conception in cows hasbeen unacceptably long (Smith and Schanbacher, 1973).

The bST treatment used to improve lactation performancemay have influenced the reproductive performance of cows.An extensive review on the effect of bST on the reproduc-tive performance of dairy cattle indicates that the use of thishormone increases the risk of a cow failing to conceive byapproximately 04 (Dohoo et al., 2003). However, recentstudies with large numbers of cows and herds indicate thatbST treatment does not affect (Judge et al., 1999; Collieret al., 2001) or even enhances fertility in dairy cows(Luna-Dominguez et al., 2000; Moreira et al., 2001 and2002; Santos et al., 2004).

The exceedingly high proportion of cows showing no oes-trous behaviour during lactation (over 17%) points towardan inappropriate oestrous detection programme. This failureto detect cows in oestrus might be mediated by attenuationof expression of oestrus in bST-treated cows. Previousstudies have shown that oestrous detection rate has beenlower in cows receiving bST (Kirby et al., 1997; Santoset al., 2004) and heifers treated with bST had a delayedonset of oestrus, fewer mounts, and oestrus of shorter dur-ation (Lefebvre and Block, 1992). Additional factors thatmight have caused the poor reproductive performance ofboth groups of cows were a combination of environmentalvariables. Maximum ambient temperature in spring andsummer in this area fluctuates between 35 and 418C (Mel-lado and Meza-Herrera, 2002) which severely disrupts thereproductive performance of dairy cows (DeRensis andScaramuzzi, 2003).

The number of services per conception was greater for theinduced cows than cows with a post-partum lactation. Thiswas not surprising because cows selected to be inducedwere not a randomly selected group of cows. These animalshad failed to conceive during the previous lactation, whichmight imply that they had reproductive problems that pre-cluded them from becoming pregnant. However, pregnancypercentages for the induced cows were acceptable, giventheir previous inability to get pregnant. These findings are inagreement with results of other researchers (Fulkerson,1978; Jordan et al., 1981; Lembowicz et al., 1982; Magliaroet al., 2004) who have also reported successful breeding in

induced cows and heifers that had previously failed tobecome pregnant.

Our work shows the effectiveness and consistency of atechnique to induce lactation in cows with reproductiveproblems, which allows cows to achieve 305 days milkyield levels .9000 kg. Despite the fact that cows thatwere induced had zero conceptions in the previous lacta-tion, a satisfactory proportion of cows eventually con-ceived and calved. With this technology there is apotential to increase income by reducing the number ofreplacement heifers and the retention in the herd of cowsof high genetic merit.

AcknowledgementsThe authors wish to thank Alfonso R. Nava Cruz for providing facili-ties, cows and drugs to carry out the present study.

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(Received 10 January 2006Accepted 22 March 2006)

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