Factors affecting gestation length in the Thoroughbred mare.

The study aims to explore the factors that may influence the length of gestation in Thoroughbred mares. Using data from 433 pregnancies, researchers used ultrasonic scanning to accurately determine gestation length and investigated the impact of variables such as foal sex, month of birth, and mare age.

Overview of Research

• The researchers conducted a detailed study involving data from 433 Thoroughbred mare pregnancies. The main aim was to investigate how different factors impact the length of gestation.
• An accuracy method, sequential ultrasonic scanning, was used to measure the true length of gestation, from fertilisation to parturition. Prior research mainly focused on the mating-parturition interval.
• The average gestation length was determined to be around 344.1 days. However, the research highlighted a significant range, with viable foals resulting from gestation lengths of 315 to 388 days.

Findings of the Study

• The sex of the foal had a significant impact on the length of gestation. Pregnancies carrying colt foals (male) were longer, with an average length of 346.2 days, compared to fillies (female), which had a shorter gestation length of 342.4 days.
• The month of birth was found to also significantly affect gestation length. Foals born in January had the shortest gestation lengths while those delivered in April had the longest.
• Contrary to what might be expected, other variables such as the mare’s age, the year of birth, the stallion’s age, the stud farm, and the interval between ovulation and mating did not have a significant influence on the gestation length.

Conclusion and Clinical Importance

• The researchers concluded that the findings of a wide gestation length range, all resulting in viable foals, are noteworthy. Such information is particularly valuable for the classification of dysmaturity in foals.
• It has been suggested that mares carrying colt foals due to give birth in the middle of the breeding season (April) are more likely to have longer gestation lengths.