Twin Lamb Disease – Who’s at risk?
- Ewes during late gestation
- Animals with multiple foetuses
- Over conditioned ewe
- Under conditioned ewe
How is Twin Lamb Disease caused?
In late gestation the energy requirement of each fetus increases significantly. Therefore the more lambs the ewe is carrying the greater the energy demand. The liver increases glucose production to try and provide enough to the fetus(es) and the ewe, however this is preferentially directed to support the fetus(es). Therefore if not enough glucose is available this leaves the ewe energy deficient. If this happens mobilization of fat stores is increased in late gestation as a way to assure adequate energy for the increased demands of the developing fetus(es) and impending lactation. However, in a negative energy balance, the greater mobilisation of fats may overwhelm the liver’s capacity and result in a fatty liver.
Ewes who are over conditioned (BCS >4), under conditioned (BCS <2) and twin / triplet carriers may quickly shift from subclinical ketosis to clinical pregnancy toxemia if feed intake is acutely curtailed by such events as adverse weather, transport, handling or other concomitant disease (footrot, pneumonia, etc).
Most cases develop 1–3 weeks before parturition, however it can be seen as early as 6 weeks before lambing. Initially animals may spend more time lying, progressing to listlessness, aimless walking, muscle twitching or fine muscle tremors, and grinding of the teeth. This progresses (generally over 2–4 days) to blindness, ataxia, and finally sternal recumbency, coma, and death.
Twin Lamb Management & Prevention:
BCS should be assessed at breeding and mid-gestation. We’re probably late for that, so if you’re concerned about a group, it might be better to test them now. Blood sampling a selection of ewes from each management group, approx. 3 weeks prior to lambing can help detect inadequate energy at a group level, allowing for changes to be made to the diet.
Ewes should not enter the last 6 week of gestation with a BCS <2.5; this can be prevented by good feeding management, eg. Adequate feeder space for pregnant animals, managing groups based on BCS and fetal numbers. However, it is important not to try and reduce the BCS in over-conditioned females during late gestation. Instead these ewes must be monitored closely for pregnancy toxaemia and improvements made in advance the next breeding year.