To understand the different parts of the estrous cycle.

To understand the hormonal changes during the estrous cycle.

To understand how the estrous cycle coordinates the events of female reproduction so it can be successful.

Learning Objectives

Proestrus

Tertiary follicle(s) and oocytes undergo final maturation Estrogen levels

Female starts to become receptive - Estrogen prepares uterus and oviducts for sperm transport and fertilization - Estrogen initiates uterine changes for later embryo development

Anestrus

Female is not cycling (No expression of heat over time)

Cow has a 21 Day Estrous Cycle: Day 0 first Day of Standing Heat

Day 17-20 (Follicular Phase)

Prior to estrus, CL is undergoing regression, progesteronelevels fall below 1 ng/mL which allows final follicular development

One dominant follicle - Graafian StageStimulated to final maturation by FSH and LH

Estrogen

Smooth muscle contractions and cilia movement

Uterine glands and oviduct secretion

ESTRUS

Picture provided by Dr. Robert P. Wettemann

Estrus

Female in heat

High estrogens cause LH surge

LH surge causes ovulation

LH surge initiates corpus luteum formation

- Day of Standing heat! Day 0 of estrous cycle Lasts 12 to 20 hours in cow

Estrogen from the Graafian follicle stimulate increase in GnRHwhich stimulates increase in LH

GnRH increases to cause a large increase in LH (surge release)Ovulation occurs during estrus in ewe, sow and mare but metestrus in cow

Following ovulation - LH stimulates development of luteal cellsfrom the granulosa and thecal cells of the ovulated follicle wall.Theca and granulosa cells luteinize by LH stimulation to differentiate in luteal cells

Metestrus

Estrogen levels have decreased

Corpus luteum is forming

Progesterone levels start to

Progesterone begins preparing the uterus for the embryo Embryo partially develops in the oviduct and moves into the uterus

Day 2-4 of Estrous Cycle

In cow, ovulation occurs after the end of estrus

Graafian follicle has ovulated

Developing from Corpus Hemorrhagicum

Second increase in FSH occurs to stimulate anotherwave of follicular development

Moves into uterus on Day 4 - 5 depending on species

Diestrus

Maximum corpus luteum size High progesterone levels inhibit final follicular development, ovulation and estrus

Embryo continues to develop in the uterus Embryo signals the uterus it is present - no CL regression

If embryo is not present - uterus releases PGF2 to cause CL regression If CL regresses, progesterone in blood decreases and Graafian follicle(s) begin final development that occurs in proestrus for ovulation at estrus.

Day 5 - 17 of Estrous Cycle

Mature at Day 12 of estrous cycle

Inhibits final maturation of follicle and estrusNegative feedback on GnRH

Estrous Cycle starts over!!!!

Hormonal Profiles During the Estrous Cycle

ng = nanogram 10-9 grams LH, FSH, Progesteronepg = picogram 10-12 grams Estrogen, PGF2

Follicle will become atretic and regress as a new follicle grows to ovulate with CL regression

Increases for CLregression Second increase of FSH for

follicle development. Inhibinis low as is progesterone

When progesterone is less than 1 ng/ml it usually means the cowhas regressed the CLand is coming into heatduring the estrous cycle

Estrus

LH surgefor ovulation

First FollicularWave

Second FollicularWave

Estrus Estrus

Adapted from Ginther, O.J. 1992. 2nd EditionReproductive Biology of the Mare. p288

Mare

Phases of the Estrous Cycle

Follicular

Luteal

Phase of the female estrous cycle when she is underestrogen stimulation Proestrus and Estrus

Phase of the female estrous cycle when she is underprogesterone stimulation Metestrus and Diestrus

Species Variation in Estrous Cycle Characteristics

Estrous Cycle EWE SOW COW MARE

Length ofEstrous Cycle 14 - 19 Days 18 - 22 Days 18 - 24 Days 16 - 24 Days

Length of Estrus 24 - 36 hours 48 - 72 hours 12 - 19 hours 2 - 11 Days

Time ofOvulation

24 - 36 hoursAfter the onset

of estrus

35 - 45 hoursAfter the onset

of estrus

10 - 11 hoursAfter the end

of estrus

1 - 2 DaysBefore the

end of estrus

Time of AI12 - 18 hours

After the onsetof estrus

16 - 14 hoursAfter the onset ofestrus and again8 - 24 hours later

7 - 18 hoursAfter onsetof estrus

Second day andevery other day

in estrus

To understand how estrus synchronization works and how to use it successfully.

Learning Objective

Estrus synchronization:

Why

1. Group females for parturition:

a. Labor, Calving period

b. More uniform weaning weights.

2. Reduce time required for estrus detection.

3. Eliminate estrus detection with timed insemination:

Reduce calving season

Hopefully in future, not always most efficient!!!

Cattle:

Prostaglandins: PGF2

Lutalyse - Natural compound 25 mg dose I.M.

Estrumate - Analogue 500 g dose I.M.

Prosolvin - Analogue 15 mg dose I.M.

Bovilene - Analogue 1 mg dose s.q.

Equimate - Analogue used in Mare

Half-life in blood 2-3 min

3-4 hrs

2 hrs

18-24 hrs

Principle - Regress active corpus luteum

Regresses Day 5-17 corpus luteum. In estrus 2-5 days after injection heifers ~50 hours cows ~72 hours

~60-65% of herd should respond to injection. To get whole herd synchronized, give 2nd injection 11 days after 1st Cows responding to 1st injection have day 6-9 corpora lutea Cows which did not respond to 1st injection now have day 6-17 corpora lutea

PGF2 is not effective between Day 0 - 4 of Estrous Cycle

To single one time injection

11 Days following 1st injection

Therefore, all cows now have a CL which will respond to PGF2 on day 11

Reasons for variation of response. Young and old corpora lutea may respond different

Heifers react sooner than cows

Animal may be pregnant - Abortion

Females do not have a corpora luteum, i.e. are anestrus

Older CL have a larger mass Day 6-9 CL in heat within 40-50 hrs Day 10 -16 CL in heat within 60-72hrs

Difference in body weightCan adjust dosage based on body weight for largerbreeds - standard dose Lutalyse 25 mg/1100 lbs give additional 5 mg/500 lbs over 1100 lbs

Brahman cattle respond poorly to the two injectionsystem of PGF2

Recommended:

Inject and breed all responders

Inject 2nd treatment 11 days later to all those not bred to 1st injection and breed on estrus detection

Management Consideration:

Have proper facilities to handle animals Good reproductive records

Have enough A.I. technician help

Be sure cows & heifers cycling

Use good fertility semen

One technician/100 cows will cause problemsShould be around 30-50 cows/technician

Anestrus cows don’t respond to PGF2

No CL!!!!!!

Breeding with prostaglandins:

Conception Rate 1. Breed 80 hours after 2nd injection 31 - 80 %

2. Breed based on estrus after PGF2 67%

3. Control cows bred based on estrus 75%

Based on estrus - Breed 12 hours after the 1st observed estrus activity

Timed AI - variation in response over 2-5 days

AM/PM rule - Twice daily heat detection

Improving ovulation synchronization

48 hours after PGF2 -Give GnRH Cause LH surge; achieved slight increase in conception rates

Cystorelin (GnRH Analogue)

Maybe a better quality CL.Improve conception rate 3-4%

Used mostly in problem breeding cows

Use of progestogens for Estrus synchronization

Principle:

Maintain the cow under the influence of progesterone until corpus luteum regresses, remove progesterone -animal respond to progesterone with estrus 2-5 days later.

Administration:

Injection

Feed

Implant

Pessary or Control Internal Drug Release (CIDR)

Time Consuming

Mix in ration

Place in ear

Place in Vagina

Synchromate B system:

Inject 5 mg estradiol valerate & 3 mg norgestomet Implant Norgestomet (Progestagen) 6 mg

Remove implant 9 days later

Breed 48 to 60 hours later or 54 hours later

Estradiol - Luteolytic to d 3-9 corpora lutea Norgestomet - Inhibits early C.L. development

Day 1

Injection allows for rapid increase in progestin in bloodwhile the implant initiates its release over several hours

Rapid decrease in progestin in blood allows animal to return to heat 2 to 3 days

If you use timed AI at 54 hoursBetter to heat check and breed

Therefore treatment blocks proestrus,estrus and early CLdevelopment. Wait 9 days for diestrus cows to regress CL

Sychromate B System can be used on noncyclingcows which may induce them to come into heat.

System is not dependent on having a CL as with the prostaglandin system.

However, cows need to be in good condition and close to cycling to respond

Brahman cattle recommend to implant norgestometNo Injection - Estradiol causes a problemInject PGF2 on Day 8 and pull implant on Day 9

Feed progestogen for 9 days

Prevents estrus in diestrus and proestrus animals

Give PGF2 on Day 8 to regress C.L.'s

Remove progestogen on Day 9 Cows are in heat in 2-5 days

Melengesterol Acetate (MGA) System

(0.5 mg/head/day)

AlternativeFeed MGA for 14 days - Don’t breed on first heat (poor fertility)Inject PGF2 16 days after withdrawal of MGA and breed onestrus detection

EAZI-BREED CIDR System

Insert CIDR (progestin) with CIDIROL capsule (estrogen)in vagina

Day 6 inject with PGF2

Remove CIDR Day 7 and breed on heat detection

Can inject with CIDIROL on Day 8 and breed by timedinsemination 50 hours from CIDR removal

EAZI-BREEDEAZI-BREEDCIDRCIDR

Insert CIDRInsert CIDRwith CIDIROLwith CIDIROLcapsulecapsule

Day 6Day 6

RemoveRemoveCIDRCIDR

Detect EstrusDetect Estrusor or

InseminateInseminateFixed-timeFixed-time50 hours50 hours

Inject PG

Day 7Day 7Beef Cow

Day 9-11Day 9-11Day 8Day 8

InjectInject2mL2mL

CIDIROLCIDIROL

7 Days

Ewe estrus synchronization:

Implant progestogen for 12-14 days Remove implant, ewes in heat in 36-60 hours

May use PMSG at implant removal to stimulate follicular growth

Fertility good 1 ram/10 ewes

Use 1/2 of a new norgestomet implant

400 - 800 IU

Procedure will also work with CIDR and Pessary (Vaginal Sponge

Can use PGF2 if during the breeding season Give 20 mg Lutalyse 9 days apart - No Effect If Anestrus

Sow estrus synchronization:

PGF2 will not cause C.L. regression until day 12 of the cycle

Common progestogens will synchronize estrus but cause ovarian cysts

Progestogen -

Allyl trenobolone fed at 20 mg/head/day for 18 days - remove from feed - in heat in 4-8 days. Fertility normal - a minor incidence of cysts.

Reason - LH binds to luteal cell receptor with strongaffinity following ovulation and is not released until day 12Repeated injections over two to three days will regress CLbefore Day 12 but is not practical

In Horse tradename Regumate is effective

Prepubertal gilts (noncycling) can be effectivelysynchronized with P.G. 600

P.G. 600 400 IU PMSG (eCG) and 200 IU HCG

Gilts cannot be cycling

Need to be greater than 51/2 months of age

Gilts should express heat 3-4 days following treatment

Mare estrus synchronization:

Luteolytic PGF2 in diestrus, in heat in 4-5 days

Use of prostaglandins in horses:

Equimate (Fluprosterol)

~1/5 cow dose

Mare CL more sensitive than cow, ewe

Will only work during diestrus when CL is presentRemember heat is over 5-11 days

Give 250 g

If you use Lutalyse or Estrumate

Problems with smooth muscle stimulatingproperties of PGF2 which occur within 15 mins

Side Effects:1. Sweating in neck, shoulders and central abdominal region2. Increase Heart rate and Respiration3. Increase motility of GI Tract (Colic)

These should disappear within 1 hourTreatments with PGF2 Mares can exhibit what is called Prolonged Diestrus Caused by persistent luteal function- CL form after ovulation fails to undergo luteolysis during normal diestrus - remains 3-4 weeks-CL maybe deep - unable to produce enough progesterone for stimulation of endometrial PGF2 release or caused by low grade uterine infectionFailure of embryo to survive but extended CL lifespan as innormal pregnancy Equimate can be used to induce estrus

when mares arrive to be bred by a stud

Use of progestins in horses Regumate

.044 mg/Kg body weight in feed Feed for 12 days or 15 days without equimate injection Remove from feed; give equimate In heat 3-4 days later

Can inject progesterone daily 150-200 mg i.m.

Liquid Regumate 1 mL/110lbs

Remember will not ovulate until day 8 of estrus

Utilization:

1. Can use on show mares to suppress heat during events2. Transport mare to breeding farm to time estrus3. Regulate number of mares in heat to utilize a stallion over time. Synchronize mating