Shapes of Lactation Curves of F1 (Holstein X Zebu) Cows in the Humid Tropic of Veracruz, México

The aim of this study was to characterize the lactation curves in F1 (Holstein x Zebu) dairy cows in a farm located in the humid tropic of Mexico. Lactation curves were modeled using four mathematical models (including the incomplete gamma function, Wilmink, Dijkstra and Ali and Schaeffer models) on actual daily milk yield records. Estimators of the lactation parameters for each model were computed for each cow by nonlinear regression using Powell algorithm in the software Scientist for Windows , version 2. The shape of lactation curves was determined by the sign of each parameter from every lactation curve in each model. The adjustment criteria considered to compare models were correlation, R2, coefficient of determination and model selection criterion. The effects of parity, calving year and calving season were studied. A total of 61,320 observations from 219 complete lactations of 68 cows were used. Ali-Shaeffer model fitted nine different curve shapes, but three accounted for 76% of them all. Dijkstra model fitted only one curve shape with all the parameters being positive. In turn, Wood and Wilmink models fitted three different curves shapes each one, but two forms in each case represented 98% of all the fitted curves. For its highest values in the R2, Coefficient of determination, Correlation and Model Selection Criterion. Ali and Schaeffer model was the best one for characterizing the curve of milk production of F1 Holstein X zebu cows, but more research on the topic is required to reach significant recommendations.