Alternative models for genetic evaluation of feed intake by Afrikaner cattle
The objectives of this study were to evaluate statistical models of potential utility for genetic evaluation of feed intake and to estimate the (co)variance components and genetic parameters that would be necessary for their use in a national cattle evaluation scheme. Data were from Afrikaner bulls that were tested between 1974 and 2016 in Phases C (n = 1 250) and D (n = 11 083) of the National Beef Recording and Improvement Scheme. Statistical analyses in which the number of traits varied and contemporary group effects were considered either random or fixed were conducted using multiple-trait derivative-free restricted maximum likelihood. Contemporary group effects were important. When they were considered random, the estimated phenotypic variance of feed intake increased and its heritability reduced from approximately 0.43 ± 0.09 to approximately 0.30 ± 0.06. Use of average daily gain, recorded either concurrently with the feed intake measure (ADGC) or from related bulls reared on-farm (ADGD), had relatively little effect on estimated heritability of feed intake. Thus, considering contemporary group effects random consistently increased the accuracy of the estimated breeding values. Relatively small genetic correlations between ADGC and ADGD complicated the ultimate application of data recorded in Phase C and the use of data recorded in Phase D in decoupling the phenotypes for feed intake and growth in an evaluation of feed efficiency. Some modification of testing procedures may be necessary to facilitate this application of the results.
Keywords: accuracy, contemporary group, genetic parameters, performance testing