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