Effect of ewe live weight on the level of response to steroid
immunisation
J.F. Smith, K.S. Maclean, L.T. McGowan, I.R. Potts
Ruakura Animal Research Station, Ministry of Agriculture and
Fisheries, Hamilton
Proceedings of the New Zealand Society of Animal Production.
1985, 45: 184-186
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.
Keywords: NZSAPAB;
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Last Updated 03-05-1997
