The Condition

Vaginal prolapse occurs in pregnant ewes 2-4 weeks before lambing. The incidence in many flocks may exceed 5%, with up to 10% mortality before lambing and a further 2-3% culled shortly after (Hosie, 1989). Lambs produced by affected ewes are often stillborn or die soon after.

Many factors have been implicated in the aetiology of vaginal prolapse, such as hormonal/metabolic imbalances, overfat/overthin body condition, bulky feeds, lack of exercise, dystocia in previous pregnancies, increased abdominal pressure and foetal burden. It is likely that increased intra-abdominal pressure in late pregnancy due to bulky feeding and increased uterus size plays the most important role. Prolapses often recur in subsequent pregnancies (Hay, 1991). More prolific lowland breeds are more susceptible than hill breeds (Low and Sutherland, 1987).

The raised intra-abdominal pressure is transmitted to the flacid pelvic structures, tending to balloon the relaxed and loosely attached vaginal walls through the lips of the vulva. The exposed mucous membrane becomes dry and irritated, triggering straining often resulting in the complete eversion of the vagina and cervix (Hay, 1991).