The effect of season on the ovulatory response of Merino ewes to serum from pregnant mares.

The study investigates the effect of seasons on the ovulatory response of Merino ewes (a type of sheep) to an injection of serum derived from pregnant mares.

Objective and Experiment Set Up

• The central objective of this study was to examine how the ovulatory response of Merino ewes, a breed of sheep, changes throughout the year when these ewes are injected with serum from pregnant mares (horses).
• Two separate experiments were conducted, with the ovulation being assessed via laparoscopy, a surgical procedure used to view the organs in the abdomen.
• In the first experiment, new ewes were used each time and three different doses of the serum were given which matched to 400, 630, and 1000 international units (i.u.) of PMSG—a hormone generally used to induce ovulation.
• In the second experiment, the same set of ewes were used throughout all sessions, and they were given only one dose of the serum (equivalent to 1000 i.u. of PMSG).

Results and Findings

• The study found that the ewes’ response to ovulation did indeed vary throughout the year: the response was the poorest in spring (September) but was the greatest in autumn (March).
• Interestingly, in the second experiment, the ovulation rate of the ewes at the end of the experiment was found to be as high as at the beginning. This showed that the response of the ewes was not dependent on the number of doses of the serum administered, but rather on other factors.

Implications of the Research

• The researchers concluded that the seasonal variations in the ovulatory responsiveness of Merino ewes suggest that the sensitivity of the ovaries to gonadotrophin (a hormone that induces ovulation) might be a significant factor in controlling the seasonal ovarian activity in sheep.
• This finding could lead to more effective management of ovulation cycles in sheep, potentially increasing productivity in a shepherd or farming context.