Genetic parameters and genotype by environment interaction for feed efficiency traits in steers fed grower and finisher diets.

This study set out to examine the genetic parameters and genetic correlations of feed efficiency traits in steers (n = 490) fed grower or finisher diets in two feeding periods. A bivariate model was used to estimate phenotypic and genetic parameters using steers that received the grower and finisher diets in successive feeding periods while a repeated animal model was used to estimate the permanent environmental effects. Genetic correlations between the grower-fed and finisher-fed regimes were 0.50 ± 0.48 and 0.78 ± 0.43 for RFI and G:F, respectively. The moderate genetic correlation between the two feeding regimes may indicate the presence of genotype-by-environment interaction (GEI) for RFI. Permanent environmental effects (expressed in percentage of phenotypic variance) were detected in the grower-fed steers for ADG (38%), DMI (30%), RFI (18%) and G:F (40%) and also in the finisher-fed steers for ADG (28%), DMI (35%), MWT (23%) and RFI (10%). Heritability estimates were 0.08 ± 0.10 and 0.14 ± 0.15 for the grower-fed steers while 0.42 ± 0.16 and 0.40 ± 17 for the finisher-fed steers for RFI and G:F, respectively. The dependency of the RFI on the feeding regime may have serious implications when selecting animals in the beef industry. Due to higher cost of grains, feed efficiency in the feedlot might be over emphasized while efficiency in the cow herd and the backgrounding segments may have less emphasis. These results may also favor the retention (for subsequent breeding) of cows whose steers were efficient in the feedlot sector. Therefore, comprehensive feeding trials may be necessary in order to provide more insight into the mechanisms surrounding GEI in steers. [ABSTRACT FROM AUTHOR]