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Journal of Dairy Science Vol. 55 No. 5 581-588
© 1972 by American Dairy Science Association ®
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Standardization of Part and Complete Milk and Milk Fat Production Records1

R. E. Pearson2 and A. E. Freeman

Department of Animal Science, Iowa State University, Ames 50010

ABSTRACT

A method for correcting test-day production to a standard 30.5-day period is compared to the system of equating 30.5 times the test-day production and to the actual production, under the assumed lactation curve.

Cumulative records were obtained by summing the standardized 30.5-day periods completed by the cow. Approximately half of the 16,991 records from 12,750 Holstein cows were complete.

Sets of gross ratio age-season factors to place cumulative part lactations on a mature-equivalent, part-lactation basis were computed for two seasons and 10 cumulative lengths for milk and milk fat yields. Sixty-six age groups were considered for each set. Equivalent factors were computed with only complete lactations.

Factors for the complete length were compared with the present U.S. Department of Agriculture factors for this region. A comparison was made at each of several lengths between factors for the different seasons, milk versus milk fat, and complete versus all records. After the first several lengths, seasonal differences were the largest effects. The age by length interaction previously reported by other workers was further substantiated.

FOOTNOTES

1 Journal Paper J-6707 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project 1053 as a collaborator under the North Central Regional Project, NC-2, Improvement of Dairy Cattle Through Breeding.

2 Present address: Dairy Cattle Research Branch, ARS, USDA, Beltsville, Maryland 20705.






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Copyright © 1972 by the American Dairy Science Association ®.