In New Zealand pasture-based sheep systems, young replacement ewe lambs and those lambs to be finished for slaughter, are often preferentially fed through summer, with ewes which have just weaned their lambs given secondary priority through until their pre-mating period. This is particularly the case in hill-country environments, in which an increasing proportion of the New Zealand ewe flock is farmed. Feed efficiency, defined as residual energy intake (REI), is a measure of whether or not an animal is eating more or less than expected for its live weight and growth rate. Of interest is whether or not animals described as efficient, or inefficient during their young growth phase, when on high-quality diets, continue to be so as an adult grazing sub-optimal feed during summer periods. There is limited comparable literature in sheep. The general finding of the beef cattle work is that the young and adult measures of REI are moderately phenotypically correlated and very highly genetically correlated, although in the most comprehensive study both the young and adults were fed the same medium-quality feed (Archer et al. 2002). In dairy cattle work, they have also found that calves divergent for REI during growth are also divergent for REI when lactating, although the size of the divergence was reduced (McDonald et al. 2014)...
Proceedings of the New Zealand Society of Animal Production, Volume 77, Rotorua, 85-87, 2017
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