Mathematical Models to Describe the Lactation Curves of Fat Trait of Iranian Holstein Cattle

The objective of this study was to compare the goodness of fit of lactation curve models; Wood, Wilmink, Linear Splines (SPL), Cubic Splines (SPC), Quadratic Splines (SPQ), Cobby and Le Du, Ali Schaeffer and Legendre Polynomial (LEG), in random regression model (RRM) for fat trait of Iranian Holstein dairy cattle. For this purpose the records obtained from Test-day (TD) regarding fat (788577) yield related to their first parity were used. The genetic parameters were estimated using REML method using WOMBAT software. To compare the model, different criterion (-2Logl, AIC, BIC,LRT) were used for fat trait. Based on obtained results, RRM with SPL6 (6,6), SPQ6 (6,6), LEG (3,5) for fat yield were selected as better model to describe the lactation curves. The estimated heritabilities by best models were lower in the beginning lactation than other during lactation (0.05 for fat yield). Additive genetic correlation between adjacent test days was more than between distant test days