Fertility, ovulation and maturation of eggs in mares injected with HCG.

This research observes how the fertility, ovulation and maturation of eggs in pony mares is affected by injections of Human Chorionic Gonadotropin (HCG) from January to August, noting variations in oestrus and ovulation, successful pregnancies, and the effect of progesterone.

Overview of Research and Methodology

• The research studied pony mares over an 8 month period (January to August). The aim was to understand the effects of injecting HCG on the nutrition, duration of oestrus, length of the oestrous cycle, and ovulation and fertility of the mares.
• The mares were observed for their reproductive behaviours and characteristics. This included noting when they showed signs of oestrus (the period when a mare is sexually receptive), the duration of this period, and the consistency of their oestrous cycles.
• HCG injections were administered. Depending on the time of the year, the effects differed. The research noted ovulation and fertility after the HCG injections.
• Mares’ oestrus was inhibited by administering progesterone through vaginal devices. The interval from the withdrawal of the devices to the occurrence of oestrus was also documented.

Findings

• From January to mid-May, most mares showed signs of oestrus, but the duration was variable. Additionally, few mares ovulated because of the HCG injections.
• Between mid-May and mid-August, the oestrous cycles of the mares were regular, and HCG induced ovulation within 40-50 hours when injected intramuscularly at a dose of 1500-5000 i.u.
• The study managed to establish 20 pregnancies out of 69 mares with one timed mating following HCG injection.
• There were instances of degenerate eggs being recovered from the oviducts of mares that had recently been in oestrus, had recently ovulated, were mated or unmated, and those that were pregnant.
• Two eggs formed the first polar body pre-ovulation while it had not formed in two recently ovulated eggs. Sperm penetration occurred 10-12 hours post ovulation resulting in the second polar body formation.
• After pronuclei formation, the first cleavage division happened 20 hours post ovulation and the second division occurred 32 hours later.
• Administered progesterone inhibited oestrus, but it occurred within 1-3 days in 12 out of 20 mares once the vaginal devices were removed.