Comparison of models for describing the lactation curve of Awassi, Morkaraman and Tushin sheep

The aim of this study was to identify a suitable mathematical model for describing the lactation curve of Awassi, Morkaraman and Tushin sheep breeds and to determine breed differences. Data on milk yield of 182 Awassi, 47 Morkaraman and 74 Tushin ewes were used. Eight empirical models from the literature were used to fit the standard lactation curves. Among them the Wood model (WD) appeared the most appropriate according to mean square prediction error (MSPE), coefficient of determination (R(2)), Durbin-Watson statistic (DW), and its applicability to the data for all three breeds. There were statistically significant (P<0.05) differences among Awassi, Morkaraman and Tushin breeds in accordance with a, b and c parameters and peak yield. The Awassi breed had the highest peak yield and the Morkaraman and Tushin breeds had statistically similar lower peak yields. There were no significant differences among the parameters of the WD model except for peak yield and peak time in accordance with parities. Breed and parity interaction was significant (P<0.05) only for peak yield.