223 Evaluation of dietary characteristics and empty body chemical components affecting the relationship between heat production and metabolizable energy intake in growing beef cattle

Abstract

Abstract Metabolizable energy required for maintenance varies with diet and empty body chemical composition. The objective was to quantify the relationships of dietary characteristics and empty body chemical composition with heat production. 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 and heifers. Data analysis were performed using R statistical package for mixed models with study as random variable. Nonlinear regression of energy gain (EG) on MEI indicated the relationship was not curvilinear in this data set, likely due to lack of negative values of EG. Further analyses were conducted using a linear model. Dietary characteristics of roughage level (0–100% of diet DM) and CP (10–25% diet DM), metabolizable energy concentration (1.3–3.3 Mcal/kg DM), and roughage type were evaluated in the model. Roughage sources were categorized into no roughage, silage, hay, pellets, silage + pellets, and hay + pellets. Of the empty body chemical components, proportion of fat in the empty body (EBFp) and in the gain (EBFgp) had a significant (P < 0.001) interaction with MEI on HP. Of the dietary characteristics, roughage level and type had a significant (P < 0.001) interaction with MEI on HP; however, when both were included in the model, roughage type was not significant (P > 0.10). The final model was 47.01 ± 12.54 + 0.630 ± 0.05*MEI – 132.3 ± 64.7*EBFp + 0.0007 ± 0.0001*MEI*Roughage level + 0.753 ± 0.24*MEI*EBFp – 0.268 ± 0.032*MEI*EBFgp with an R2 of 0.919 and an AIC of 1614 compared with 0.867 and 1695 for the simple linear regression model of HP on MEI. In conclusion, greater empty body fat decreased the intercept, and greater empty body fat proportion and levels of roughage in the diet increased the slope between HP and MEI, whereas greater percentage of fat in the empty body gain decreased the slope between HP and MEI.