BRIEF COMMUNICATION: Modelling liveweight change to inform residual feed intake models in growing lambs

摘要

A research programme to investigate the genetics of Residual Feed Intake (RFI), as a measure of feed efficiency, is being established for New Zealand maternal sheep. The basis of the RFI model is to estimate the dry matter intake that should be required by an individual to support its energy requirements for maintenance and production (e.g., growth, lactation), and compare it against its actual intake. Residual feed intake studies have been conducted for decades in beef cattle (Archer et al. 1997; Kearney et al. 2004), and terminal sheep breeds (Cockrum et al. 2013) and more recently in dairy cattle (Waghorn et al. 2012). A common feature of all studies is questions surrounding what duration the trial should be, and how often the animals should be weighed. Multiple weights over time are required to generate an accurate estimate of the growth rate of the animals. The energy required for growth differs depending on the growth rates achieved, and at moderate to high growth rates, accounts for more energy, than that required for maintenance, such that inaccurate estimates of growth rate will significantly impact on the RFI estimate of an individual. Indeed, as shown by Archer et al. (1997) in cattle, longer periods of recording are required to obtainan accurate liveweight profile than are required to get repeatable estimates of feed intake, with only 35 days of feed intake data required, compared to 70 days to accurately estimate weight gain. The frequency with which animals are weighed within any of these trials varies. One option is the integration of a weigh platform in to the feeding system for multiple weights generated per day (Kearney et al. 2004), however, more commonly the weigh platform is not integrated and animals are weighed in stand-alone scales three times per week (Waghorn et al. 2012) through to monthly (Cockrum et al. 2013).