By Bruce Farquharson
The loss of lambs either at or after birth is unacceptable. Many of the losses can be prevented by improved management and feeding ewes according to their requirements. Most of this can be put in place by planning management between scanning and lamb marking.
High survival of lambs is important to have more lambs to sell and to have more ewe lambs from which to select flock replacements.
There are four major causes of perinatal deaths in lambs. These are:
The major cause of losses varies between properties. It is not regional; the cause is specific to each sheep property.
Dystocia is the result of a difficult birth. This most often occurs when the ewe has had poor growth as a weaner and does not develop good pelvic size. This can be further complicated by over-feeding ewes in late pregnancy resulting in a large lamb.
Exposure results from adverse conditions at lambing. Rain and wind combined have the greatest chilling effect. Exposure deaths can be minimised by good body condition in the lamb and provision of shelter from terrain, trees or plantings against the wind.
Starvation results from the ewe deserting her lamb. Ewes in light condition with inadequate feed will walk away from one or both lambs. Disturbance of the ewes by predators or human presence can result in lambs losing contact with the ewe.
Predation is primarily caused by foxes although eagles, pigs and wild dogs can also be destructive. With foxes the entire lamb is removed and there may be no evidence of predation. Most predators are lazy and will take the lamb that is not being defended by the ewe. Some predators are scavengers and feed off dead lambs. Vigorous predator control, selection of paddocks away from predator havens, and the use of alpacas or guardian dogs can all assist in deterring predators. However a ewe in good condition has strong mothering instincts and will protect her lamb.
Two factors are extremely important in planning lambing of the flock – these are nutrition of the ewe and provision of shelter in lambing paddocks. Ewes should maintain condition throughout pregnancy. This will ensure that lambs are of adequate birth weight, the ewe provides adequate milk for her lambs and has an improved mothering instinct to protect her lamb. The lambing paddocks should have adequate pasture cover at the start of lambing so all ewes, including later lambing ewes have adequate feed. The selected paddocks should ideally be closed up at scanning time to allow sufficient pasture growth. Ewes with twin lambs should be in paddocks with pasture covers of 2,000 kgs dm/ha and those for single lambs 1,500 kgs dm/ha.
Shelter varies between paddocks. It is a good exercise to review the lambing percentage achieved in each lambing paddock over previous years. Some paddocks consistently have higher lambing percentages. These paddocks should be allocated to the twin-bearing ewes as they provide better shelter.
Some sheep producers conduct post-mortems on a sample of dead lambs to elicit the cause of death. This is a simple technique that has been demonstrated to them by their veterinarian. Each lamb is inspected and then the thorax and abdominal cavity is opened and the presence of key signs observed. The findings are recorded along with the date, the size of the lamb, the paddock in which it died, and the weather conditions. The examination of each lamb takes less than 5 minutes to complete. At the end of lambing a discussion with their veterinarian will confirm the diagnosis, and prevention measures can be discussed.
Acceptable Performance
The following are realistic targets that competent sheep producers are achieving.
If these targets are not being attained it is recommended that producers arrange a discussion with their veterinarian so management can be improved to reduce the wastage.
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