Prediction of body weight and empty body composition using body size measurements in lactating dairy cows

Body composition and live animal measurements of Holstein-Friesian lactating dairy cows (n =146) were obtained from a large herd to represent a range of animal factors including parity, live weight (LW), body condition score (BCS), milk yield and stage of lactation. Live animal measurements were recorded 3 or 4 days prior to slaughter, including LW, BCS, milk yield, heart girth, belly girth, withers height and length. The objective was to develop prediction equations for body weight and component mass from body size measurements and other live animal data. All body size measurements were positively (P <0.001) related to LW, empty body (EB) weight (EBW), carcass weight and EB masses (kg) of lipid, CP, DM, water and ash and total GE content (MJ). The correlation coefficients (r) in these relationships were highest with heart girth (0.62 to 0.88), followed by belly girth (0.52 to 0.88) and length (0.51 to 0.83) and lowest with withers height (0.35 to 0.69). Heart girth was therefore selected as the primary predictor and a number of equations were then developed for prediction of body weight and EB mass, with the effect of parity or stage of lactation removed, where appropriate. All relationships were significant (P <0.001) and each predictor had a significant effect on the relationship (P <0.05). The adjusted R ² values in the linear/quadratic relationships of heart girth with body weight and EB masses ranged from 0.53 (lipid mass) to 0.78 (LW). Addition of a range of other live animal variables (belly girth, length and BCS) to support heart girth significantly improved all relationships, with the Cp statistic and RMSPE (root mean square prediction error) values considerably reduced and adjusted R ² values increased. These equations were evaluated through internal validation, by developing a range of similar new equations from two thirds of the present data and then validating these new equations with the remaining one third of data. The validation revealed a high prediction accuracy for LW, EBW, carcass weight and EB masses of CP, water and DM, a relatively good accuracy for EB lipid mass and total GE content, and a relatively poor accuracy for EB ash mass. In conclusion, body size measurements can be used together with other live animal factors to accurately predict body weight and EB component mass of lactating dairy cows. These equations provide an alternative approach to estimate body weight and component mass of lactating dairy cows.