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Journal of Dairy Science Vol. 43 No. 4 519-528
© 1960 by American Dairy Science Association ®
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Variables Affecting Ratio Factors for Estimating 305-Day Production from Part Lactations1

R. C. Lamb and L. D. McGilliard

Department of Dairy, Michigan State University, East Lansing

ABSTRACT

Complete lactations for 12,561 Holsteins, 2,262 Guernseys, 990 Jerseys, and 459 Brown Swiss recorded in Michigan DHIA-IBM from June 1954 through July 1957 were analyzed to ascertain the relative effects of breed, herd, age, parity, and season of freshening on the relationship of total to part milk production, and then were used to derive ratio factors for extending partial records to 305 days.

The ratio of total milk produced on ten monthly test days to milk produced on each test day was used to measure the relationship between total and part production. Components of variance of ratios indicated that lactation number had a larger influence on the total to part relationship than did age at freshening. Season of freshening also exerted an influence, but to a slightly less degree than either lactation number or age, while the effect of herd was small and unimportant. Differences between breeds existed both in the components of variance and in the total to part relationship.

Ratio factors for extending records from each of ten monthly test days and from cumulative test-day production were computed for different ages, lactation numbers, and seasons of freshening for each of the four breeds. Only small differences exist between the factors which adjust for ages and those which adjust for lactation number, indicating that either set of factors should adequately extend incomplete records. However, factors based on age are more useful in extending those records in which age at freshening and lactation number do not coincide. In practice breed, age, and season of freshening should be considered in extending partial records to 305 days.

FOOTNOTES

1 Journal Article No. 2502. Michigan Agricultural Experiment Station.






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Copyright © 1960 by the American Dairy Science Association ®.