Comparison of different lactation curve models in Sahiwal cows

Abstract

The present investigation was carried out on 12,859 fortnightly test-day milk yield records of first lactation pertaining to 643 Sahiwal cows spread over a period of 49 years (1961-2009), maintained at the National Dairy Research Institute, Karnal, India. The comparison of 3 lactation curve models, i.e. the quadratic model, gamma-type function, and mixed log function, was done using fortnightly test-day milk yield records. The mixed log function was the best fit, with the highest (88.75%) coefficient of determination (R2 value) and the lowest (0.08 kg) root mean square error (RMSE) value, whereas the lowest (56.93%) R2 value was observed in the quadratic model with maximum (0.15 kg) RMSE value. The closeness of fit of the mixed log function and gamma-type function with the observed lactation curve was almost of the same order. However, the gamma-type function gave a low peak yield, and therefore it is recommended that this function can give the best fit for low-yielding cows.