Is it possible to accurately estimate lactation curve parameters in extensive beef production systems?

Abstract

Objective: The objective was to characterize the lactation curve applying 3 different models using multiparous grazing beef cows. Materials and Methods: Milk production data from 99 British crossbred multiparous cows grazing native pastures were analyzed. Lactation was assessed 15 d postpartum and then monthly until weaning (180 d postpartum) using a milking machine after an oxytocin injection. Total milk production and lactation curve were characterized using Wood (WD) and Wilmink (WIL) models, and both were compared with spline functions. Comparison was made applying adjusted coefficient of determination (R2adj) and MSE. Results and Discussion: Cubic splines with 5 equally spaced knots (CS5) presented the best adjustment (lowest Akaike information criterion and Bayesian information criterion). The R2adj values were 0.55, 0.54, and 0.53 (the greater the better) and MSE values were 2.54, 2.59, and 2.47 (the lower the better) for WD, WIL, and CS5, respectively. Estimated milk production for the lactation period was 1,277, 1,255, and 1,195 kg for WD, WIL, and CS5, respectively. Milk peak was predicted to happen at 32, 25, and 36 d postpartum, with a production of 8.74, 8.21, and 8.40 kg for WD, WIL, and CS5, respectively. No differences were evident in the lactation curves (95% CI). Implications and Applications: The proposed method and frequency used to assess grazing beef cattle milk production accurately estimate the lactation curve. The Wood model, used worldwide, was a precise estimator of the lactation curve, which in our case was verified applying splines. These results provide key information to calculate grazing beef cow requirements.