A deterministic simulation model for the evaluation of reproductive performance in Thoroughbred mares.

The research article presents a deterministic simulation model built to study and evaluate the reproductive performance of Thoroughbred mares. The model examines how potential changes in various parameters like conception rate, early pregnancy loss rate, and fetal loss rate may affect the herd’s overall foaling percentage.

Model Development

• The model was created to provide an evaluation of the reproductive performance of Thoroughbred mares. A deterministic simulation model was preferred given its ability to precisely predict outcomes based on specific initial conditions.
• The study utilized the model to calculate the herd level asymptotic foaling percentage (AFP), which is used to assess the performance of stable mare herds. AFP is essentially the proportion of mare pregnancies that result in a live foal.
• The model operated under the assumption that mares were only bred during the breeding season. This is consistent with standard Thoroughbred breeding practices.

Investigated Variables and Sensitivities

• The research explored the impact of early pregnancy loss and fetal loss on the mare’s reproductive performance. Both factors can significantly influence a mare’s ability to successfully bear a live foal.
• The study also investigated how changes in conception rate (CR), early pregnancy loss rate (EPLR), fetal loss rate (FLR), and postpartum mating interval (PMI) affected AFP. These factors were chosen given their direct relationship with mare maternity outcomes.

Results and Analysis

• The study found that AFP was sensitive to changes in early pregnancy loss rate, fetal loss rate, and conception rate. This highlights the importance of closely monitoring these factors in breeding programs to maximize mare fertility rates.
• The model compared AFP for two types of postpartum first mating schedules: mating during the first postpartum estrus cycle (also known as foal heat) and first mating during the subsequent cycle. Results showed that mating during foal heat resulted in higher AFP—even accounting for potential decreases in reproductive parameters—which suggests efficiency in this practice.
• Furthermore, the model suggested that even if mares did not mate during foal heat, AFP could still be improved by shortening the estrus cycle with the administration of Prostaglandin (PGF). PGF is a hormone known to induce estrus in mares, and can, therefore, be used to manipulate their breeding schedule for better outcomes.