Predicting requirements for growth, maturity, and body reserves in dairy cattle

The 1996 National Research Council Nutrient Requirements of Beef Cattle equations used to compute growth requirements, target weights, and energy reserves were modified and evaluated for use with dairy cattle. Coefficients used to compute target weights during growth and equations used to predict body weights (BW) for each condition score in computing energy reserves were modified. Equations used to compute net energy and protein requirements for growth were evaluated with data from studies of body composition changes in Holstein heifers; this model accounted for 96% of the variation in energy retained with a 4% bias. Coefficients used to compute target growth rates and BW were evaluated with data from Holstein heifer growth studies. Actual and target shrunk weight gain and BW values were before first pregnancy, 0.82 versus 0.87 kg/d with a 370-kg weight at first pregnancy versus a target of 352 kg; during the first pregnancy, 0.63 versus 0.69 kg/d with a weight at post first calving of 533 versus 545 kg; and first lactation, 0.136 versus 0.104 kg/d with a second post-calving weight of 592 kg versus 590 kg. The equations used to predict body reserves from BW and condition score were evaluated with data from a study of body composition associated with body condition score in Holstein cows; the revised model accounted for 96% of the variation in body fat and predicted 80 kg shrunk BW change per body condition score compared to 85 kg observed.