Estrus cycle synchronization in Cows

Estrus Cycle Synchronization

It is a process of bringing a group of animals into heat at the same time through hormonal intervention.
Estrus cycle

Why to synchronize animals?
Synchronization facilitates artificial insemination (AI)
Synchronization program improves the reproductive performance of the herd.
Earlier and more concentrated calving
Synchronization program helps to decrease the average days in milk (DIM) of the herd, decrease the DIM at first service, and decrease the calving interval.
It may be helpful in repeat breeders if it is due to short or silent heat.
Synchronization program ensures that most of the cows have been covered during
the breeding season.
Synchronization program makes management easy.
Uniform calf crop is achieved.
Animals calve in a short time span allowing better management and also increased milk yield.
Synchronization program decreases the number of open cows at farm and hence increases farm profitability.
 Understanding of the Estrous Cycle:
Bovine estrous cycle ranges from 18-24 days. There are four stages of the cycle.
Proestrous (17-21 days)
Estrous (0-1day)
Metestrous (2-5 days)
Diestrous (6-16 days)

Estrous is the period when animal shows heat signs. All the behavioral signs are manifested by the animal in this phase. During this phase, level of estrogen is very high in the blood. In bovines ovulation takes place 10-15 hrs after the end of heat. So, the best time to inseminate the animal is at the end of the heat.

Metestrous comes after estrous and ranges from 2-5 days. In this phase corpus luteum starts to develop from corpus hemorrhagicum. There is one important point to note that in this phase corpus luteum is not responsive to prostaglandins (causes the lysis of corpus luteum) as it lacks receptors required for the action of prostaglandins.

Diestrous is the lengthiest phase of the cycle and ranges from 6-16 days. In this phase development of corpus luteum takes place. At day 12th, a fully grown crown shaped corpus luteum is present on the ovary. During this phase, corpus luteum is responsive to prostaglandins. Level of progesterone is very high due to fully mature corpus luteum.There are two to three waves of follicles during estrous cycle. Follicles develop and undergo atresia and next wave is started.

Corpus luteum starts regressing during the proestrous phase and hence level of progesterone starts decreasing in the blood that signals the hypothalamas to release GnRH (gonadotropin releasing hormone). GnRH acts on anterior pituitary to release FSH (follicle stimulating hormone). FSH is responsible for the development of the follicle. The mature follicle releases estrogen which is a
signal for the GnRH to release LH (leutenizing hormone) from the anterior pituitary. LH surge leads to ovulation and next process is repeated.

Hormones used for synchronization:
  • GnRH (gonadotropin releasing hormone)
  • Progesterone
Selection of animals:
Selection is made on following factors.
Age12-14 months16 months18 months24 months
Body weight325kg300kg275kg400kg
BCSAt least 3.5/5At least 3.5/5At least 3.5/5At least 3.5/5
Point to ponder:
  • It is better to select those animals which don’t have history of dystocea, prolapse, and RFM (retained fetal membrane) .

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