The objective of this study was to develop and validate a model to estimate the EE apparently digestible fraction from different cattle diets. True digestibility coefficients and metabolic fecal contribution were the main parameters fitted to the model. The estimation method for both parameters was based on the Lucas test. The dataset used to build the model contained 48 and 60 experimental means for lactating cows and growing and finishing cattle, respectively. Data were taken from 24 experiments (12 experiments for each animal category). Comparison between animal categories was done by using a Dummy variable. The dataset used for model validation originated from two independent trials with lactating cows and one trial with growing cattle. The true digestibility coefficient (0.8596) did not differ between animal categories. It was observed greater metabolic fecal EE for lactating cows than for growing and finishing cattle. The metabolic fecal EE did not change with different dietary EE levels (EE%), when expressed as a percentage of dietary EE. Therefore, the EE apparently digestible in the diet (EEad%) can be estimated by the following equations: EEad% = 0.8596EE% - 0.21 for lactating cows and EEad% = 0.8596EE% - 0.18 for growing and finishing cattle. The validation procedure indicated that observed and estimated values of EEad% were not different for both animal categories. It was concluded that the proposed model can improve the accuracy of total digestible nutrients prediction based on chemical composition of the diet.
apparent digestibility; Lucas test; NRC system
