Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2005
Publication Date: 6/1/2005
Citation: Williams, C.B. 2005. Technical note: a dynamic model to predict the composition of fat-free matter gains in cattle. Journal of Animal Science. 83(6):1262-1266.
Interpretive Summary: A model was developed to predict the fraction of protein in fat-free matter gains in cattle. Evaluation of the model showed that it provided accurate predictions of protein gain and that it was more accurate than using a constant fraction of protein in fat-free matter gain. This model provides a more accurate method of partitioning nutrient intake to fat and protein gain and predicting empty body gain from a known nutrient intake. The integral form of the model can be used statically to provide predictions of the average protein gain over a feeding interval. The derivative form of the model can be used in dynamic systems models to provide predictions of daily protein gain.
Technical Abstract: Composition of empty BW (EBW) was described in terms of ether-extractable lipid (FAT) and fat-free matter (FFM) and the terms dEBW, dFAT and dFFM were used to represent daily gains in these components. The dFFM is composed of protein, water, and ash, and a model was developed to predict the composition of dFFM. 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 the protein content of dFFM would be high at birth and decrease at a decreasing rate as the animal grows. 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, dFAT, and dFFM of Hereford x Angus steers from birth to 500 kg BW was simulated with a previously published model, and the model under discussion was used to predict composition of dFFM. Predicted response curves of the EBW components over the growth period were similar in shape to observed data. Predicted curvilinearity in response of protein weight against FFM weight for Hereford × 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.