204 Effect of Breed Type on Maintenance Energy Requirements and Partial Efficiency of Metabolizable Energy use in Growing/Finishing Cattle

Abstract

Abstract Consensus is lacking on whether genetic differences exist in the partial efficiency of metabolizable energy use. Genetic differences in net energy required for maintenance have been reported, but independence of body composition was not addressed. The objective was to determine contribution of genetic differences to net energy for maintenance and partial efficiency of metabolizable energy use in growing/finishing cattle independent of body composition. A literature search was performed to compile data (31 studies, 214 treatment means) on metabolizable energy intake (MEI) and composition of empty body gain in growing steers. Dietary roughage concentration and breed were recorded. Data analyses were performed using R statistical package for linear models. For analysis, breeds were categorized as British (Angus, Hereford, English crosses), Continental (Charolais, Simmental, Limousin), Crossbred (British x Continental breeds), Dairy (Holstein), Double-muscled (Belgian Blue, Piedmontese), and Heat-tolerant (Boran, Brahman, Tuli). The base regression model of log10 of heat production on MEI had R2 of 0.8830 and intercept of 1.912 (81.6 kcal/kg.75). Inclusion of breed type significantly (P < 0.0001) affected the intercept and slope of the model. Dietary roughage concentration, empty body fat percentage, and energy retained as protein or fat, but not empty body protein percentage, explained a significant amount of variation (P < 0.01) resulting in R2 of 0.9851. In this final model, Heat-tolerant breeds had 12% lesser (P < 0.05) net energy for maintenance than British with Continental, Crossbred, and Double-muscle being intermediate, and Dairy had 27% greater (P < 0.05) net energy for maintenance than other breed types. Also, breed type by MEI interaction was significant (P < 0.0001) with Dairy having lesser (P < 0.05) slope than other breeds, and Heat-tolerant having greater slope than British. In conclusion, breed type affected net energy for maintenance and partial efficiency of metabolizable energy use after accounting for body composition and dietary roughage concentration suggesting that genetic variation exists.