Genetic and phenotypic relationships among different measures of growth and feed efficiency in young Charolais bulls

Performance and progeny test data on young Charolais bulls in France were used to estimate genetic and phenotypic variation, and correlations among postweaning growth and feed efficiency traits. Records on 510 performance test bulls born from 1985 to 1989 and 792 progeny test bulls born from 1988 to 1997 were used, plus available pedigree information (total n = 5493). Feed intake for performance Lest bulls was restricted to achieve growth rate of 1.5 kg/day, while that for progeny test bulls was ad libitum. Nine growth and feed efficiency traits were studied. (Co)variances were estimated by multivariate REML analysis using an animal model. The focus of the study was on the progeny test bulls but all analyses were done simultaneously with two performance test traits which were used to select most of the sires of the progeny test bulls. All the traits to 15 months of age were moderately heritable (0.31-0.48), highlighting the fact that genetic improvement can potentially be made in any of these traits. Feed conversion ratio (FCR) was highly correlated genetically with relative growth rate (r = -0.90) and Kleiber ratio (r = -0.81), two traits which do not require measurement of feed intake. The measure of residual feed intake (RFI) where the expected feed intake (EFI) was calculated from the dataset was highly correlated genetically (r = 0.89) with RFI where EFI was calculated from feeding standards formulae. Both RFI measures were highly correlated genetically (r greater than or equal to 0.85) with FCR. (C) 2001 Elsevier Science B.V. All rights reserved.