Genetic correlations of steer growth, fatness and IGF-I with feed intake and efficiency in two tropically adapted genotypes

Costs associated with feeding represent one of the major inputs for beef cattle producers.Arthur et al. (2001) and Robinson and Oddy (2004) demonstrated that net feed intake (NFI: defined as feed eaten, less what is expected based on the animal’s growth rate and body weight) was heritable (h 2 = 0.18 to 0.51). Robinson and Oddy (2004) estimated geneticcorrelations of daily feed intake (FI) and NFI with body composition traits and reported that animals with lower NFI produced leaner carcases. Given the high costs of FI measurement, there is interest in indirect means of predicting genetic merit for NFI. Moore et al. (2005) reported a moderate positive correlation (r g = 0.54) between NFI and blood plasma levels of IGF-I (IGF-I) measured post-weaning in Angus seedstock cattle. Johnston et al. (2002) found a genetic correlation of 0.56 between IGF-I concentration and NFI in feedlot tested cattle. These experiments examined NFI in predominantly Bos taurus breeds. As part of a larger study described by Burrow et al. (2003), genetic parameters for FI and NFI were estimated for two genotypes of tropically adapted cattle. This paper presents the initial findings of this research, including the genetic relationships of FI and NFI with steer production traits and IGF-I measurements, taken from weaning to feedlot exit.