Abstract:

Data on 718 lactation records pertaining to Brown Swiss cows reared in Research Farm of College of Agriculture at Atatürk University were analyzed to find out the effects of some systematic environmental factors on the parameters of lactation curve obtained from different models. For this purpose, Wood model based on gamma function, inverse polinomial function and reduced lactation persistency models were utilized in this study. The effects of calving year, calving season as well as parity and calving season on the LnA, b, c values obtained from Wood model were significant (P<0.05) respectively. On the other hand, the effects of parity and calving season as well as calving season on A1 and A2 calculated from inverse polinomial function were highly significant (P<0.01) respectively. The effects of parity and calving year on Yp, t1 and the influences of calving year on t and b3 determined from reduced lactation persistency models were highly significant (P<0.01). It was concluded that the phenotypic values must be standardized according to significant environmental factors before a selection regarding with lactation curve parameters

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