BY: Dr Ken Geenty
The immense value of ewes in breeding or terminal lamb enterprises is often underestimated. In addition to the dollars, they are reliable and resilient workhorses, pumping out lambs year after year. Their use in pasture management during the four months each year not pregnant or lactating is a bonus.
However ewe losses, particularly during pregnancy, are very costly, with both capital stock and unborn lambs included. The most common causes such as vaginal prolapses or bearings and metabolic disorders can be minimised with alert animal health and sound grazing management. Ewe losses are greatest in ewes carrying multiple lambs, adding to overall costs, along with increased labour and potential vet fees.
Most ewe deaths are in late pregnancy due to ewes being cast, suffering milk fever or sleepy sickness, having bearings, and sometimes being exposed to fertiliser toxicity.
Milk fever due to calcium deficiency can be caused by disruptions in feeding by the likes of shearing, vaccinating, or crutching in late pregnancy. It is most common in ewes bearing multiple lambs when they quite rapidly become unsteady and drowsy, with muscle trembling. Classic early milk fever signs are a green discharge from the nose. Symptoms may be confused with sleepy sickness (pregnancy toxaemia), but milk fever is distinguishable by complete relaxation of the stomach muscles and an appearance of flabbiness. Treatment is an injection of calcium borogluconate.
Most ewe deaths are in late pregnancy due to ewes being cast, suffering milk fever or sleepy sickness, having bearings, and sometimes being exposed to fertiliser toxicity.
Sleepy sickness occurs when the ewe’s energy intake is considerably below requirements. Mobilisation of body fat produces ketones, which make the ewe drowsy, with awkward movements and an appearance of being blind. If not treated with a sugary solution or Ketol, the ewe will rapidly decline, go down, and slip into a coma before dying. Early diagnosis is the key, when ewes should be promptly offered additional high quality feed.
There is little or no scientific evidence on causes of bearings. Excessive intra-abdominal pressure in late pregnancy with multiple lambs and often bulky feed predisposes ewes to bearings. The problem can also occur just after lambing, but less frequently.
Scientific and farming observations indicate risk factors may include dietary, hormonal or mineral imbalances, putting on excessive weight in late pregnancy, under-exercised ewes, running pregnant ewes on hill country, and tail length from docking being too short.
Farm surveys have shown prevalence is generally greatest in aged ewes, often with a history of multiple lambs, and sometimes in flocks experiencing a sudden surge in lambing percentage. Incidences varied considerably between affected farms and years, ranging from 4-12% of ewes. Average incidence was less than 1% across all farms. This means on average 20 ewes and 40 lambs are involved in a 2000 ewe flock, with possibly a high proportion lost.
Although there are no known ways of avoiding bearings, sound nutrition to maintain middle-of-the-road body condition score (BCS) right through to lamb drop is a good strategy. At the same time, consider the predisposing risk factors listed above and ensure good feed quality with no mineral deficiencies or imbalances.
Because most cases of bearings occur in pregnant ewes with multiple lambs, a good practice is to separate ewes carrying twins and triplets for preferential management on flatter paddocks. This can only be done if pregnancy scanning has been carried out between 60 and 90 days of pregnancy. Importantly, ewes with multiple lambs should not have restricted feeding during the final 6-8 weeks of pregnancy in the hope this will reduce bearings. Rather, it could cause lowered lamb birth weights with increased lamb deaths due to miss-mothering and starvation.
Successful treatment of bearings relies on early detection, gentle and clean replacement using a mild disinfectant, and effective retention. Preferably a vet should have been consulted for correct procedures. It’s likely ewes will successfully recover and lamb normally but the probability of repeating the problem in subsequent lambings is high. Therefore ewes should be clearly identified for either culling or preferential future treatment.
- Ken Geenty is a primary industries consultant.
