Factors affecting live foal rates of Thoroughbred mares that undergo manual twin elimination.

The study focuses on understanding the factors affecting the live birth rates after manual twin elimination process in Thoroughbred mares. The results showcased that the age of the mares, specifically those above 9 years old, was linked to decreased pregnancy rate after the twin reduction procedure.

Objective

The research objective was to ascertain the factors associated with a successful outcome, a live birth, in Thoroughbred mares that underwent manual twin elimination between the 13th and 17th day of their ovulation cycle, performed by a single operator.

Methods

• The study was conducted retrospectively with the use of breeding records and the Jockey Club records of registered Thoroughbred mares with twin pregnancies (n=129).
• These mares were matched with mares of the similar age, parity (number of pregnancies), farm location and month of breeding with a single pregnancy (n=127) to ensure the comparability of both groups.
• Various factors like the location of embryonic vesicles, age of the mare, reproductive status, parity, month of breeding, size of the vesicle and the plasma progesterone concentration at the time pregnancy diagnosis were studied and their impact on the live birth rate were assessed.

Results

• The study found that the position of embryonic vesicles at the time of manual elimination, the number of previous pregnancies, and the month of breeding had no effect on the live birth rate.
• However, it was observed that mares older than 9 years had a lower live birth rate (71.8%) as compared to those 9 years or younger (87.1%, P<0.05).
• Mares older than 9 years that underwent the twin reduction procedure experienced a higher rate of pregnancy loss (34.8%) compared to their age-matched controls (20%, P<0.005).
• The mean plasma progesterone concentration in mares that had a twin elimination procedure was higher than in the control group when matched on the same post ovulation day. Importantly, the plasma progesterone concentrations had no significant effect on whether the mares lost pregnancy or delivered a live foal.

Conclusions

The study concluded that the age of Thoroughbred mares, particularly those above 9 years, is associated with a decreased pregnancy rate following twin reduction. The research insight provides a valuable understanding of the factors which can potentially affect the successful outcome of a live foal after the performance of manual twin elimination procedure.