By Dr Colin Trengove, Pro Ag Consulting
Marking percentages are always a discussion point with variable results this year because of the late break to the season across most of the State in 2021. The inevitable consequence was increased ewe and lamb loss due to pregnancy toxaemia and hypocalcaemia.
Failure to appreciate the energy and mineral needs of the late pregnant ewe is a common finding and even more so with a delayed break. Lack of feed in autumn necessitates prolonged grain feeding. Hay alone does not have sufficient energy density to meet the needs of late pregnancy with death due to pregnancy toxaemia (energy deficiency or ‘twin lamb disease’) the consequence. Grain invariably has insufficient calcium to meet the needs for developing foetuses leading to hypocalcaemia (‘milk fever’) if this is not addressed. Calcium is supplied in a variety of pre-lambing lick supplements or simply a 50:50 stock lime & salt mix.
As a rule, those who scan their ewes for multiple pregnancies, monitor ewe condition through pregnancy and adjust feeding rates accordingly have achieved very good marking percentages including 70-80% survival in twins. It does require forward planning to ensure that there is enough supplementary feed of sufficient quality in reserve, but there has never been a more profitable time to focus on optimal ewe and lamb survival.
Abortions occasionally account for lamb loss but these are usually sporadic events associated with recently introduced or straying sheep. There are several micro-organisms capable of causing abortion, but Campylobacter fetus (formerly ‘vibriosis’) is the bacteria that most commonly causes problems around SA. Where Campylobacter has been recently diagnosed a vaccination program can readily prevent further occurrence of the disease. Recent serological surveys indicate that many flocks have been exposed to Toxoplasmosis spread by cats, but there is little evidence to indicate that it causes significant lamb loss.
Another cause of low lambing percentage is clover disease which has been recognised for over 50 years in SA but mostly tends to go unnoticed. Ewes become more infertile with increasing exposure to oestrogenic varieties of sub clovers – namely: Yarloop, Dinninup, Dwalganup and Geraldton. These clovers tend to be very persistent and are most easily identified in spring by their leaf markings and flower characteristics. Infertility risk increases when they represent more than 20% of the feed on offer.
Losses of around 30% between scanning and lamb marking are still the norm and there is much research currently directed at reducing this. Approximately 70% of this loss occurs in the first 2 days post-lambing and so having ewes in condition score 3 with adequate feed and shelter, away from predators goes a long way to reducing these losses. Ask about joining a LifeTime Ewe Management group if you would like to know more.
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