Age-Month Adjustment Factors for Milk, Fat, and Protein Yields in Holstein Cattle

Open Access
Publisher Website
Google Scholar
Abstract
Age-month factors were developed for milk, fat, and protein yields. Records used in the analysis consisted of 769,410 lactation records of Holstein cows freshening in New York [USA] and New Jersey [USA] from July 1982 through August 1984. The mixed model used to describe the data contained fixed effects due to an overall mean, age-month of calving, herd-year, and random effects due to cow and error terms. There were 26 age groups by 12 mo of freshening for a total of 312 age-month estimates for each of the three yield traits. Results showed a definite age by month interaction with age being more important for younger cows while month effects assumed more importance as the cow matures. Multiplicative age-month correction factors were developed and are presented along with plots of the age-month factors for milk, fat, and protein yield. Factors differed for three yield traits. Fat and protein factors were higher than corresponding factors for milk.