Observations on the length and angle of declination of the vulva and its relation to fertility in the mare.

The researchers in this study have devised an instrument to measure aspects of the mare’s vulva, with the goal of improving fertility rates. They found that making changes based on these measurements can significantly increase pregnancy rates.

Research Objective and Methodology

• The objective of the study was to develop a tool, termed the “Caslick Index,” that could aid in determining whether a mare requires Caslick’s operation—a procedure to prevent air from entering the vagina, promoting better reproductive health. The research team was interested in helping mares that do not show the usual signs of needing this procedure.
• The metric used in this exercise was derived from two measurements: the length (“l”) and angle of declination (“a”) of the mare’s vulva. A product of these two measurements (la) constituted this Caslick Index.

Key Findings

• The researchers noted a significant increase in the value of “l” as the mare’s age increased. This shows that the length of the vulva in breeding mares is subject to change over time and may have implications for fertility.
• The study analyzed data from 9020 mares and found that mares that had undergone Caslick’s operation and those with a Caslick Index of less than 150 had higher pregnancy rates than those not operated on or with a Caslick Index above 150.
• The researchers suggest that a Caslick Index of 100 or above should warrant a meticulous clinical examination of the mare’s genital tract, particularly in mares not currently showing clinical signs of reproductive issues.
• The study also demonstrated that mares that had not given birth (nulliparous) and had undergone Caslick’s operation for racing purposes showed a significantly higher rate of pregnancy than those that had not undergone the procedure and were in their first year at stud.

Implications

• This research seeks to broaden the scope by which the necessity of Caslick’s operation is determined, basing the decision not only on evident symptoms but also on a novel index developed by the researchers.
• The findings offer a potentially effective way to boost pregnancy rates in mare populations and enhance their fertility care. With proper application and further studies, the Caslick Index can form part of standard mare clinical evaluations for reproductive health.