Seasonal Age Correction Factors for 305 Day Milk Yield in Holstein Cattle

Abstract

Total of 3780 lactation records of Holstein Friesian cattle kept at a commercial farm (Dena Farm) in Egypt, during the period from 1988 to 1996 were used. Fixed effects of month and year of calving and age at calving as a regression and random effects of sire and cow within sire on 305 day milk yield were used. Least squares analysis of variance showed significant effects of month and year of calving, age at calving, sire and cow within sires. Including age at calving as a polynomial regression of the second degree in the model yielded significant regression coefficients. The partial linear and quadratic regression coefficients of age at calving on 305 day milk yield were 8.49 ± 1.76 kg/mo and-0.51 ± 0.05 kg/mo 2 , respectively. A set of multiplicative age factors was derived for 305 day milk yield for each season of calving and for all data by fitting a second degree polynomial for production on age. It is suggested that there should be a separate set of age correction factors for each season of calving and for each region.