Factors affecting lactation curves of friesian cows in Saudi Arabia

First lactation records of 203 Friesian cows were utilized to estimate parameters of the lactation curve using the incomplete gamma function and to determine the importance of sex, season of calving and the regression of these parameters on coefficients of dam weight, calf weight and age at first calving. Sex of calf had nonsignificant effects on the estimated parameters of the lactation curve. However, aborted cows had lactation curves different from the normally delivered cows. Season of calving had a significant effect on the initial milk yield (Log (a» and rate of increase to peak production (b). Dam weight had a highly significant effect (P<0.01) on log (a) and a significant (P<0.05) effect on the seasonal variation<br>other than season of calving (cosine (v». Its regression coefficients for both parameters were 0.004 :t 0.001 and 0.0005 :t 0.0003, respectively. However, dam age had no effect. Calf weight had a highly significant effect (P