[The prevention of pneumovagina and the effect of the Caslick operation on fertility: a retrospective study].

Mares with a large vulvar orifice have an increased risk of pneumovagina, which is associated with reduced fertility. Treatment is by means of the Caslick operation, by which size of the vulvar orifice is reduced. Factors that influence the occurrence of pneumovagina are the age and fertility status of the mare. In this study the risk factors for pneumovagina and the effect of the Caslick operation on fertility were investigated. In 1994, 1995, and 1996 a total of 967 mares were sent for service at a stud. Of these mares, 116 underwent a Caslick operation. The operated mares were older than the non-operated mares. Mares younger than 5 years had a lower chance of pneumovagina than mares aged 5-12 years, but mares aged 13 and older had an increased chance. Foals and barren mares were more likely than maiden mares to develop pneumovagina. Fertility was 67% among the non-operated mares and 51% among the operated mares, even though, after the operation, the vulvar orifice of the operated mares was the same as that of the non-operated mares. This difference in fertility may be due to secondary endometritis that continues to exist after the operation. Further research is needed to determine whether mares with pneumovagina should also be treated for endometritis at the time of surgery.