Prediction of energy balance in high yielding dairy cows with test-day information

This study used a previously developed model to predict herd mean energy ba lance of the first 12 wk of lactation from test-day information. The predic tions were compared with calculated energy balance based on feed analysis a nd to changes in body weight. Seven independent feeding trials including 43 diets (519 lactations, 254 cows; 1987 to 1996) were used. Conventional die ts were discriminated from nonconventional diets by significant differences between mean calculated energy balance of subtrial diets versus control di ets. The total difference between group means of predicted minus calculated energy balance was positive throughout the observed lactation period. It w as lowest (5 to 9 MJ of net energy for lactation) during negative energy ba lance of the conventional diets in wk 2 to 7 when 18 to 50% of the total di fference was due to random variation. Because of this difference, both pred icted and calculated energy balances were compared to body weight change as a reference for true energy balance. Body weight change was adjusted for r umen fill. While calculated energy balance tended to be negative at times w hen cows gained weight, predicted energy balance was positive. Cows fed non conventional diets gained weight, while calculated energy balance was extre mely negative, whereas predicted energy balance based on test-day informati on was positive. We concluded that the prediction difference was relatively small when standard rations were used, and that nonconventional rations bi ased predicted energy balance to a lesser extent than calculated energy bal ance. Estimating energy balance based on test-day information appears feasi ble.