Ovarian response of cows following pregnant mare serum gonadotrophin treatment during two successive estrous cycles.

The research article discusses a study that used pregnant mare serum gonadotrophin (PMSG) to induce multiple ovulations in thirteen cows across two successive estrous cycles to understand how it affects the ovarian response.

Research Design and Methodology

• The study involved thirteen cows of different breeds namely 8 Holsteins, 3 Ayrshire, and 2 Shorthorn, aged between 3 to 7 years. They were treated with PMSG during two successive estrous cycles.
• The gonadotrophin was injected on Day 16 of the cycle (where the day estrus started is considered as Day 0) and then again on Day 16 of the next cycle for 10 cows.
• In the case of 3 cows, the second PMSG injection was administered 21 days after the first injection.
• The dosage of PMSG injected during the first cycle was 3,000 IU for one group of 6 cows (Group A) and 2,000 IU for the second group of 7 cows (Group B).
• In the second cycle, these doses were reversed for each cow i.e., Group A received 2,000 IU and Group B received 3,000 IU.
• The cows were then slaughtered 10 to 14 days after the second PMSG treatment to evaluate the effects of the injection.

Key Findings

• Response to PMSG was evaluated based on the number of ovulations and total follicular response, calculated by adding the number of ovulations to the count of follicles greater than 10 mm diameter.
• The mean ovulation rate and mean total follicular response for Group A cows were 19.5 and 20.7, respectively, showing a significant increase in ovulation with this treatment.
• For Group B, the mean ovulation rate and mean total follicular response were 10.7 and 29.1, respectively. While two cows in Group B hadn’t ovulated before slaughter, the mean ovulation rate of the remaining five cows was 15.0.
• The research concludes that substantial superovulation responses can be obtained after two successive PMSG treatments in two successive estrous cycles.