Survival of day-4 embryos from young, normal mares and aged, subfertile mares after transfer to normal recipient mares.

The study examines the survival rate of day-4 embryos from both young, healthy mares and older, subfertile mares after being transferred to healthy recipient mares. The research found that the embryonic loss rate in the latter group was much higher than in the former, suggesting that the embryonic loss may be due to inherent flaws in the embryos or potential effects of their initial environment.

Key Findings

• The study showed that the estimated embryonic loss rate between Days 4 and 14 after ovulation for young, normal mares (9%) was significantly lower than the estimated embryonic loss rate for aged subfertile mares (62%). This difference was statistically significant and could suggest a decline in fertility as mares age.
• Fertilization rates were also compared. Normal mares had a 96% fertilization rate, while subfertile mares had a lower rate of 81%. Though the difference fell shy of the traditional threshold for statistical significance (p<0.05), this still indicated a possible fertility issue among older, subfertile mares.

Embryo Transfer and Outcome

• Day-4 embryos were collected from both normal and subfertile mares. This was done to test a hypothesis that the high incidence of embryonic loss in subfertile mares was related to inherent defects in the embryos. These embryos were then transferred to the uteri of synchronized, normal recipient mares.
• The results supported the afore-mentioned hypothesis, as the study showed embryo survival rates were significantly higher for Day-4 embryos from normal mares compared to subfertile ones. This could mean that the offspring of subfertile mares face higher risks during early development.

Possible Reasons for Embryo Loss

• The cause of embryo loss among the subfertile mares could be due to inherent defects within the embryos. Alternatively, it might result from the influence of the oviducal environment before Day 4 after ovulation. The oviducal environment can have negative effects on the embryos, which could be particularly detrimental during the early stages of development.

Implications of the Study

• This study provides vital information on equine reproduction, specifically regarding fertility rates and the survival of embryos in mares.
• Understanding the causes of embryo loss in mares could frame the development of strategies to increase the survival rate of horse embryos, and hence, improve the overall fertility performance in equine species.