Submitted to: Feedinfo News Service
Publication Type: Popular Publication
Publication Acceptance Date: 9/15/2005
Publication Date: 9/16/2005
Citation: Williams, C.B. 2005. Predicting the protein content of fat-free matter gains in beef cattle. Feedinfo News Service Scientific Reviews. September 2005. Available: http://www.feedinfo.com.
Technical Abstract: A dynamic computer model was developed to predict the protein content of fat-free matter gains in cattle. Composition of empty body weight (EBW) was described in terms of ether-extractable lipid (FAT) and fat-free matter (FFM). The FFM is composed of protein, water, and ash and the terms dEBW and dFFM were used to represent daily gains in EBW and FFM. The conceptual approach used in model development was based on experimental data that showed as cattle grew from birth to maturity: a) the water content of FFM decreased and the protein and ash content increased, b) the protein content of FFM increased at a decreasing rate, and c) the protein to ash ratio in the FFM dry matter was approximately constant. These results suggest that as cattle grow and mature, dFFM would contain increasing amounts of protein, and as the dFFM content of dEBW decreased the protein content of dFFM would also decrease. Mathematical functions were formulated to represent these concepts, and a set of equations were derived to predict composition of dFFM. The protein content of dFFM was predicted as a function of the fraction of dEBW that was dFFM, FAT content of EBW, and dFFM. A fixed protein-to-ash ratio of 4.1:1 was used to calculate the amount of ash, and water was obtained as a residual. Gain in EBW and dFFM of Hereford x Angus steers from birth to 500 kg BW was simulated with a previously published model, and the above model was used to predict composition of dFFM. Predicted response curves of the EBW components over the growing period were similar in shape to observed data. Predicted curvilinearity in response of protein weight against FFM weight for Hereford x Angus steers was similar to observed data. Compared to using a constant value for the protein fraction of dFFM, the model provided more accurate predictions of dEBW in an independent evaluation data set. These results support the conclusion that the model is capable of accurately representing the real system.