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Maximum Likelihood Estimates of Age Effects

U. S. Department of Agriculture, Agricultural Research Service, Animal Husbandry Research Division, Beltsville, Maryland

ABSTRACT

The relative merits of maximum likelihood estimates of age factors were examined with 24,636 lactations from registered Holsteins in Iowa Dairy Herd Improvement Association herds. A table containing maximum-likelihood estimates of age effects on milk and fat yield was presented. Maximum likelihood (ML) factors were compared to gross and paired comparison factors. Gross factors were more similar to the ML factors than were the paired factors, particularly at older ages. It was concluded that sampling errors in the ML factors are within acceptable limits for the volume of data employed. ML factors should be used in preference to gross factors in situations where accuracy is of critical importance. ML factors possess the properties of unbiasedness and minimum variance; they are based upon both intra-cow and inter-cow information.

¹ Present address: Biometrical Services, ARS, Beltsville, Maryland.

² Present address: Department of Dairy Science, Ohio State University, Columbus, Ohio.