Fitting five models to describe milk production curve for Khuzestani Buffaloes of Iran in different parities and seasons

Abstract

In this research, to evaluate the lactation curve of Khuzestani buffaloes and to determine its describing function, 89140 test day records of buffaloes, collected in 1991 to 2015, were used. All the studied functions (Wood, Wilmink, Parabolic, Mixed Logarithmic and Inverse Polynomial models) were fitted using NLIN procedure of SAS 9.1 software. The results showed that the lactation curve of Khuzestani buffaloes became more typical from 4^th and 6^th lactation, as it was completed with three steps of increasing production, peak yield and decreasing phase in the 7^th and 8^th parities. Based on the criteria, studied functions did not have the same performance for lactation curve so that the Wood function was the best model. According to best function, peak of milk production increased from the first lactation and its maximum value was obtained for the 8^th lactation. The time of peak yield for the studied curves were vary variable (between 79 and 90 days). In terms of estimated amount for persistency, there was not much difference among curves of different lactation, so that obtained values were very close together. We can say the lactation curves of studied buffaloes were flat, as the difference between the beginning and the end of production was very low. The results also showed that among different calving seasons, the Parabolic function had the best fitting for lactation curve of buffaloes with calving in spring, autumn and winter seasons and the Mixed Logarithmic function was the best for buffaloes with calving season of summer.