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Regression Factors for Predicting a Succeeding Complete Lactation Milk Record from Part Lactation Records

Department of Animal Husbandry, Cornell University, Ithaca, New York

ABSTRACT

The age- and season-corrected monthly D.H.I.A. milk records of 9,036 cows in 374 New York herds, and the succeeding record of 2,358 of these cows in 226 herds, are used to develop regression factors for predicting a succeeding complete lactation milk yield from part lactation records. A single test-day record from the fourth, fifth, or sixth month of a lactation has a correlation of 0.50 with the succeeding complete lactation. This correlation is nearly as large as the correlation between two successive complete lactation yields, which is 0.55. A linear function of the first five monthly test records predicts a complete second record as accurately as the total yield of the first lactation. Linear functions for the first seven monthly records are even more accurate. Prediction equations utilizing bimonthly test records are more highly correlated (0.57) with second complete records than complete first records, and are nearly as accurate as linear functions of ten monthly test-day records.