Rate of gain and feed efficiency are very important traits in most breeding programs for growing farm animals. Rate of gain (GAIN) is usually expressed over a certain age period and feed efficiency is often expressed as residual feed intake (RFI), defined as observed feed intake (FI) minus expected feed intake based on live weight (WGT) and GAIN. In any case the basic traits recorded are always WGT and FI and other the traits are derived from these records. A bivariate longitudinal random regression model were employed on 9284 individual longitudinal records of WGT and FI from 2827 bulls of six different beef breeds that were performance tested on a central test station in Denmark. Genetic and permanent environmental covariance functions for curves of WGT and FI were estimated using Gibbs sampling. The covariance function were based on fourth order Legendre polynomials but other functions were also possible. Genetic and permanent covariance functions for curves of GAIN were estimated from the derivative of the function for WGT and finally the covariance functions were extended to curves for RFI, based on the conditional distribution of FI given WGT and GAIN. Furthermore, the covariance functions were extended to include GAIN and RFI defined over different periods of the performance test. These periods included the whole test period as normally used when predicting breeding values for GAIN and RFI for beef bulls. Breeding values and genetic parameters for derived traits such as GAIN and RFI defined both longitudinally or integrated over (parts of) of the test period can be obtained from a joint analysis of the basic records which consists of WGT and FI. The resulting covariance functions for WGT, FI, GAIN and RFI are usually singular but the procedure presented here do not suffer from the estimation problems associated with trying to define these traits individually before the genetic analysis. All results are thus estimated simultaneously and the set of parameters are consistent.
Book of Abstracts of the 64th Annual Meeting of the European Association for Animal Production, 2013
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64th Annual Meeting of the European Federation of Anmal Science, 2013