Genetics appears sometimes involved as some breeds can be more susceptible, and also some individual breeding lines can seem at particular risk.
by Suzanna Bell, Veterinary Investigation Officer, AHVLA Aberystwyth
Vaginal prolapses can occur in ewes up to 55 days before lambing, but more commonly in the last four weeks of pregnancy, or shortly after lambing. An incidence of one per cent in flocks is common with some flocks experiencing rates of more than two per cent.
Vaginal prolapses increase the risk of ewe death but can also result in abortion/stillbirths, difficulty with lambing (dystocia) and new-born lamb deaths. The timing of cases seems to coincide with the relaxation and softening of the soft tissues and bones of the birth canal, initiated by hormone changes during late pregnancy.
Genetics appears sometimes involved as some breeds can be more susceptible, and also some individual breeding lines can seem at particular risk.
Suspected factors that could increase the risk of vaginal prolapse in ewes:
1.Fat deposits in the birth canal further slackening the soft tissues: both genetics and over-feeding could influence.
2.Hormone imbalance: thought to be genetically influenced in some cases. Mouldy feed might in some cases affect the hormone balance due to the presence of toxins that are similar in action to hormones.
3.Possibly hypocalcaemia (low calcium): although many cases have normal calcium levels.
4.A short docked tail: this may weaken the muscles/ligaments attaching to the tail bones.
5.Lambing difficulties in the previous pregnancy.
Previous vaginal prolapse: 40 per cent of ewes will prolapse again in subsequent pregnancies.
Increased abdominal pressure is also believed to be a major causal factor in combination with one or some of the above factors:
1.Large pregnant uterus (womb): multiple foetuses within the uterus is associated with a much increased risk, suggested as a five times increased risk for twins and even up to eleven/twelve times the risk for triplet bearing ewes.
2.Large amounts of intra-abdominal fat: over-conditioned, over fed ewes. Particularly if the condition score is greater than four.
3.Rumen distension: from feeding bulky feeds, an excess of dietary fibre or gas build up secondary to acidosis/grain over-load.
Other suggested predisposing factors in some flocks include:Lack of exercise: prolapses occur more commonly in housed than outdoor flocks, longer periods lying down may also influence.
Poor body condition: condition score of less than 2.
Lying on steep slopes: sheep tend to lie with the head uphill and gravity may encourage a prolapse in some cases.
Develop a plan with your veterinary surgeon to reduce the risk of vaginal prolapse to the minimum.
That was a great article. Thank you we experienced our first prolapse this year. Thank you