TABLE OF CONTENTS

Estrus Synchronization in Cows

Estrus synchronization in cows is a reproductive management technique used to control or manipulate the estrous cycle so that a group of cows comes into heat at approximately the same time.

This is typically achieved through the administration of hormonal treatments such as prostaglandins, progesterone devices, or gonadotropin-releasing hormone (GnRH).

Synchronization allows for more efficient breeding, either through artificial insemination or natural mating, leading to better herd fertility management, a more uniform calf crop, and easier planning of labor and resources on the farm.

Advantages

Potential advantages of estrus synchronization in large dairy herds:

Better control of calving interval.
Reduction on dependence on heat detection.
Reduction of errors in heat detection.
Increased reproduction with the same number of cows.
Maintain same production with fewer numbers of cows.
Increased number of calves per cow.
Increased economic use of AI.
Schedule entry of heifers into the milking herd.
Reduce labour.

Synchronization Products

Synchronization products control the estrous cycle by influencing structures that are present on the ovary:

Prostaglandins (PG)
Estradiol Benzoate
Progesterone, MGA and Norgestomet
Gonadotropin Releasing Hormone (GnRH)

1. Prostaglandins (PG)

PG regulates a female’s estrous cycle by causing “luteolysis” or regression of the CL when it is present on the ovary.

A synthetic prostaglandin will mimic natural PG release from the uterus and will cause CL regression. Because the CL produces progesterone, PG eliminates the “progesterone block” and allows follicles to grow and subsequent ovulation to occur.

Recommended Time to Inject Prostaglandin in the Cow

Females with a CL on their ovary when they receive an injection of PG will usually exhibit estrus 2 to 5 days later. An injection of PG will only regress a CL that is 6 to 17 days old in the 21-day estrous cycle.

After the progesterone block is removed, there is an increase in follicle growth and therefore, an increase in estrogen production and heat and subsequent ovulation will occur 2 to 5 days after the PG injection.

2. Estradiol Benzoate

Estradiol benzoate, the estrogen used in the Syncro-Mate B protocol, will cause regression of a CL that is 1 to 5 days old. This is the primary reason for using estradiol instead of a prostaglandin.

3. Progesterone, MGA and Norgestomet

Progesterone, MGA and Norgestomet (in the Syncro-Mate B protocol) “hold” the female from exhibiting heat. During a normal estrous cycle, the CL on the ovary produces progesterone.

Feeding (MGA) or implanting (Syncro-Mate B) progesterone in females will play the same role as progesterone being produced by the CL.

Progestins will not allow the follicle to ovulate or allow the female to exhibit heat until the synthetic progestin is removed.

4. Gonadotropin Releasing Hormone (GnRH)

Gonadotrophin releasing hormone causes the release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) from the anterior pituitary.

The target tissue for LH and FSH is the ovary. The ovary needs these hormones to grow follicles that produce the egg. In a synchronization program, LH and FSH will grow follicles and also are a part of the process that causes ovulation (release of the egg from the dominant follicle). Because LH and FSH are involved in follicle maturation, these two hormones also support estrogen production from the follicle.

An elevated blood concentration of estrogen is associated with ovulation and bringing the animal into standing heat.

Initially estrus control was attempted with progesterone. Though estrus and ovulation was controlled, the conception rate in the first service was poor. In the 1960’s, the treatment was mostly oral treatment with progestogens and it was termed ‘grouping’.

Criteria for Successful Controlled Breeding

Animal Requirement

Animal must be disease free, especially of reproductive tract.
Heifer must have reached maturity with proper weight >200-250 kgs.
Nutrition must be adequate with the animal in positive balance.
Adequate postpartum interval of 45-60 days should be there.
For prostaglandins it is important that the animals must be cycling.
The animal should have a normal non-pregnant reproductive tract.

Management Requirement

Proper timing is essential, once the program is initiated it must be carried through all steps in proper sequence and at proper times.
Good semen quality is an essential requirement. Under present condition existing in the field, this is very important.
Good AI technique must be followed.

Short-term Progesterone Therapy

(1) Synchromate-B System / Progesterone + Oestrogen

It is an ear implant inserted into the outer pinna of the ear subcutaneously.
At the time of ear implant insertion, 2 ml of injection containing 3 mg Norgestomet and 5 mg oestradiol valerate is administered.
The ear implant contains 6 mg Norgestomet.
Total hormone content: 5 mg oestradiol + 9 mg Norgestomet.
Role of oestrogen: Luteolytic in cows, horses but not in swine.
It causes lysis of the corpus luteum.
The ear implant is removed after 9 days.
AI (Artificial Insemination) is performed 48–72 hours after implant removal.
This protocol can be used in both cyclical and non-cyclical animals.

(2) Progesterone + PGF₂α

CIDR or TRIU-B is kept in the vagina for 9 days.
In cyclical animals, PGF₂α is injected on Day-8 after CIDR or TRIU-B insertion.
On Day-9, CIDR or TRIU-B is removed.
AI is carried out on Day-11 and Day-12, after 48–72 hours of removal of CIDR or TRIU-B.

Protocol for True Anestrus

In case of true anoestrus cows, CIDR or TRIU-B is inserted and kept in place for 9 days.

On Day-8, GnRH or eCG may be injected intramuscularly:

eCG: 400–500 IU
GnRH: 10–20 µg

CIDR or TRIU-B is removed on Day-9 and Artificial Insemination (AI) is performed on Day-11 and Day-12.

Synchronization of Ovulation

Synchronization of the ovulation is a precise method to bring the animal into oestrus along with ensuring ovulation.

Two methods used for synchronization of the ovulation:

Ovsynch Protocol
Co-synch Protocol

1. Ovsynch Protocol

It is a GPG protocol.
It involves Inj. GnRH, Inj. PGF₂α, Inj. GnRH.
The Ovsynch protocol was designed by Pursley et al. in 1995.
Irrespective of the stage of cycle, the protocol can be used.
It can be employed in both cyclical and non-cyclical animals.

Protocol:

Day-0: Inj. GnRH @ 10–20 µg I/M.
Day-7: Inj. PGF₂α @ 25 mg natural / 500 µg synthetic.
Day-9: Inj. GnRH given in the evening.
Day-10: Artificial Insemination (AI), i.e., 14–16 hours after the second GnRH injection, AI is done.

First (Day-0) GnRH injection luteinized or ovulates the follicle present in the ovary. PGF₂α injection causes luteolysis of the luteinized follicle along with the corpus luteum, if any.

The second GnRH injection increases LH secretion, matures follicles, and confirms ovulation.

2. Co-synch Protocol

Day-0: Inj. GnRH
Day-7: Inj. PGF₂α
Day-10: AI + Inj. GnRH