Nutritional evaluation of diets. Simulation model of digestion and passage of nutrients through the rumen-reticulum

To evaluate the nutritional behaviour of simple and complex diets provided under different feeding regimes, a stochastic, dynamic and predictive simulation model was developed. Feed fractions, considered in the model were soluble non-structural carbohydrates (SNSC), insoluble non-structural carbohydrates (INSC), INSC degradation rate (kdINSC), fractional passage rate (kp), neutral detergent fibre (NDF), NDF potentially digestible (PNDF), PNDF degradation rate (kdPNDF), soluble crude protein (SCP), insoluble crude protein (ICP), ICP potentially degradable (PICP), and PICP degradation rate (kdPICP). Animal characteristics considered in the model, were live weight and physiological status (lactation and/or pregnancy). Variables inherent to management practices were amounts and schedule of DM offered to the animals. The model was subjected to validation for a wide range of experimental conditions. Predictions of total DM and forage DM intakes (and therefore the estimate of the substitution of forage for concentrate) had an R2 = 0.95 and 0.92, respectively. Prediction of NDF digestibility had an R2 = 0.61 in a smaller range of experimental conditions.