214 Assessment of Equations Relating Empty Body Chemical Components in Growing/Finishing Cattle

Existing equations to estimate empty body chemical composition were developed over 40 years ago using different cattle genetics. The objective of this analysis was to evaluate existing equations using cattle genetics from then to today. A literature search was performed to identify experiments measuring empty body chemical composition by proximate analysis resulting in 198 treatment means from 25 experiments since 1976. Three sets of equations were used to compute empty body chemical composition assuming empty body water was known: 1) Garrett and Hinman (1969; 10.2527/jas1969.2811), 2) Gil et al. (1970: 10.2527/jas1970.313459x), and 3) Ferrell et al. (1976; 10.2527/jas1976.4251158x). Mean (SD) empty body water, fat and protein were 59.91 (6.32), 17.58 (7.89), and 18.24 (2.02) % of EBW, respectively. For all equations, simultaneous testing of intercept equal to zero and slope equal to 1 indicated that the intercept and slope for fat, protein, ash and energy were different than zero and one, respectively. The concordance correlation coefficient (CCC) was high (> 0.85) for fat and energy, but low (< 0.50) for protein and ash for all equations. Mean bias for fat, protein, ash, and energy ranged from -19.58 to -3.50%, 1.62 to 15.84%, -2.22 to 14.15%, and -6.09 to -0.63%, respectively, with Eq. 1 having the MB closest to 0 for protein, and Eq. 3 having the MB closest to 0 for fat, ash, and energy. Publication year as a continuous variable was a significant predictor of the difference between observed and predicted values for all components. Fat and energy had greater overpredicted whereas, protein and ash had greater underprediction in more recent publications. In conclusion, existing equations provide similar precision, but differ in accuracy to predict empty body chemical composition. The trend for greater bias in more recent publication years indicates the need to reevaluate relationships among empty body chemical components using current cattle genetics.