Residual energy intake (REI), also referred to as residual feed intake, is one way of describing feed efficiency, and is an estimate of whether or not an animal is eating more or less than expected for its weight and growth rate. The REI trait has been investigated in a number of production-animal species, but only pilot study data exists for New Zealand sheep. This paper investigates phenotypic variability in the trait of REI for a cohort of 197 growing ewe lambs. The animals were approximately nine months old at the commencement of the trial. Their daily intake of a lucerne pellet-diet was measured for 56 days using an automated feeder that recorded weight of feed consumed in real time. The animals were weighed twice weekly. The standard REI model involves fitting metabolic mid-test live weight and live weight gain to predict energy intake. Both measurements fitted were significant (P<0.001), with an overall R2 for the model of 0.78. Grouping of the animals in to Low-, Mid- and High-efficiency groups revealed a 24% difference in energy intake between the low and high groups which is consistent with studies in other species. The comparison of attributes of the efficiency groups did reveal differences in fatness with the high-efficiency animals fatter at the start of the data collection, but they did not lay down as much fat during the trial as the low-efficiency group. Given the phenotypic variability is consistent with that observed in other production-animal species, additional cohorts will be measured in the coming years to generate a data set to investigate the genetics of the trait, and further investigate the role of fat within the REI model.
Proceedings of the New Zealand Society of Animal Production, Volume 76, Adelaide, 34-37, 2016
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