A trial was conducted in 1984 to examine the effect of live weight on response to immunisation in 3 groups of 200 Coopworth ewes differentially fed from weaning in December to reach 3 live weights in March (40, 50 and 60 kg). Half of the ewes in each group were immunised with Fecundin(r) and further subdivided into 2 levels of nutrition (*1.5 v 3.4 kg DM/ewe/d) for 4 weeks prior to a synchronised mating. Ovulation rate (OR); percent ewes lambing to first cycle (CR); lambs born per ewe lambing (LB/EL); percentage ova wastage (PRMO); and lambs born per ewe joi9ned (LB/EJ) were determined. Immunisation had a significant effect on all parameters (OR= +0.56; CR= -7.6%; LB/EL= +0.37, PFMO +10.1%; LB/EJ= 0.25). Ewe mating weight significantly increased OR (+0.37), CR (+19.5%), LB/EL (+0.25) and LB/EJ (+0.34) but did not significantly influence ova wastage. Premating nutrition significantly increased OR (+0.23), LB/EL (+0.09) and PFMO (+8.9%), but not LB/EJ. The regressions on mean group mating weight of OR and LB/EL in first cycle showed similar slopes for the immunised and control ewes. Nutritionally induced differences in ewe mating weight therefore did not influence these responses to immunisation. The response to LB/EJ was greater in the heavier ewes and reflected the effects of live weight on conception rate and embryonic loss.

GH, Davis, SF Crosbie, and JF Smith

Proceedings of the New Zealand Society of Animal Production, Volume 45, , 178-180, 1985
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