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Abstract : |
A linear mixed model was used to study the fixed effects of month of calving, year of calving and parity, and the random effects of sire and cow within sire on annualized milk yield (AMY). The study was conducted on 3056 lactation records of 803 Holstein Friesian cows. A least squares analysis of variance showed significant effects of all factors on AMY (P less than 0.05 or P less than 0.01). Including days open (DO) and days dry DP) as a polynomial regression of the second degree in the model yielded significant regression coefficients (P less than 0.01). The partial linear and quadratic regression of AMY on DO were -8.890.62 kg/d and 0.01270.0019 kg/d2, respectively. The partial linear and quadratic regression coefficients (P less than 0.01). The partial linear and quadratic regression of AMY on DO were -8.890.62 kg/d and 0.01270.0019 kg/d2, respectively. The partial linear and quadratic regression coefficients of AMY on DP were -2.300.45 kg/d and 0.0050.0016 kg/d2, respectively. Maximum production in the current lactations including the calf crop expressed in kilograms of milk was attained when cows were bred as early as possible after parturition. Therefore, a reduction of DO is a desirable goal of dairy men. , A linear mixed model was used to study the fixed effects of month of calving, year of calving and parity, and the random effects of sire and cow within sire on annualized milk yield (AMY). The study was conducted on 3056 lactation records of 803 Holstein Friesian cows. A least squares analysis of variance showed significant effects of all factors on AMY (P less than 0.05 or P less than 0.01). Including days open (DO) and days dry DP) as a polynomial regression of the second degree in the model yielded significant regression coefficients (P less than 0.01). The partial linear and quadratic regression of AMY on DO were -8.89?0.62 kg/d and 0.0127?0.0019 kg/d2, respectively. The partial linear and quadratic regression coefficients (P less than 0.01). The partial linear and quadratic regression of AMY on DO were -8.89?0.62 kg/d and 0.0127?0.0019 kg/d2, respectively. The partial linear and quadratic regression coefficients of AMY on DP were -2.30?0.45 kg/d and 0.005?0.0016 kg/d2, respectively. Maximum production in the current lactations including the calf crop expressed in kilograms of milk was attained when cows were bred as early as possible after parturition. Therefore, a reduction of DO is a desirable goal of dairy men., |
