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Factors for Estimating Daily Yield of Milk, Fat, and Protein from a Single Milking for Herds Milked Twice a Day¹

Dairy Science Department, University of Florida, Gainesville 32611

G. R. Wiggans

Animal Improvement Programs Laboratory, Agricultural Research Service, United States Department of Agriculture, Beltsville, MD 20705

ABSTRACT

Existing factors for estimating daily yield from the yield of a single milking were analyzed by comparing estimated daily yields with milk sold for herds in the northeastern United States. Milk yield was overestimated consistently compared with bulk tank milk weights. Estimates of protein yield showed lack of fit by length of preceding interval. Milk factors were developed from testing plans with one measured milking (a.m.-p.m. testing plans) and from those with two measured milkings; resulting factors were essentially the same. New factors for components were developed from data from a.m.-p.m. testing plans because component percentages for individual milkings are determined only for a.m.-p.m. plans. Factors were reciprocals of portion of day's yield, which was modeled as a linear effect of preceding interval. Slopes for milk and protein were essentially the same. Slope for fat was about 70% of those for milk and protein, which indicated that fat was affected less by interval than were milk and protein. Therefore, fat percentage from a single milking should be adjusted to estimate day's fat percentage. Analysis of residuals from analysis for milk indicated an effect by stage of lactation. An additive adjustment is suggested. Data were collected from herds enrolled in a.m.-p.m. testing plans in the northeastern United States after the new factors had been implemented for more than 1 yr. They indicated that most lack of fit from old factors had been eliminated.

¹ Florida Agricultural Experiment Station Journal Series Number 6177.