Application of neutral detergent fiber in modeling feed intake, lactation response, and body weight changes in dairy...

A computer simulation model was developed using theoretical equations to predict DM intake in dairy cattle when the NDF and energy content of the diet and the energy requirements of the animal were known. An adjustment factor for NDF quality was determined to account for differences in intake with legume-based and grass-based diets when formulated at equal NDF content. Mathematical functions were developed from actual data to describe body reserve tissue mobilization and deposition and used to refine the determination of energy requirements and energy balance of the animal. Actual data on milk production and BW changes of Holstein cows under three feeding systems (individual concentrate, one- and two-group total mixed rations) were used to evaluate the model. There was good agreement between observed and predicted production responses, except for the one group total mixed ration, where daily milk yield was overpredicted during early lactation. Further calculations showed that the amount of available CP was too low to support the high milk production that the model predicted in early lactation with the one-group feeding system. This problem was corrected by incorporating a protein restriction on milk production using NRC guidelines.