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Ratio Factors to Estimate 305-Day Production from Lactation Records in Progress1

Department of Dairy, Michigan State University, East Lansing

ABSTRACT

Complete lactation records for 24,602 Holsteins, 4,309 Guernseys, 1,878 Jerseys, and 892 Brown Swiss were used to develop ratios to extend milk and fat records to 305 days. Breed, age, and season of freshening influenced the relationship between total and part production sufficiently to require adjustment in extending records in progress. Separate factors should be used for milk and fat records. To remove adequately the effects of age, different factors for milk are needed for cows calving before 36 months of age and for those 36 months and older, while separate factors are needed for fat records initiated at less than 36 months, 36–47 months, and 48 months and older. The effects of season of freshening can be counteracted by factors for records started during a four-month spring and summer period apart from those for the other eight months. The months in the seasons differ between milk and fat records.

Ratio factors for separately extending milk and fat records from each of ten monthly test days and from cumulative test-day production are presented for different ages and seasons of freshening for each of the four breeds.

¹ Journal Article no. 4001. Michigan Agricultural Experiment Station.

² Present address: Dairy Cattle Research Branch, ARS, USDA, Department of Dairy Science, Utah State University, Logan.