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Variation in Part-Lactation and Whole-Lactation Feed Efficiency of Holstein Cows

Animal Husbandry Research Division, USDA, Beltsville, Maryland 20705

ABSTRACT

Data from 1,004 lactations of Holsteins in the Beltsville herd were studied to characterize variation in whole- and part-lactation measures of feed efficiency, kilograms fat-corrected milk per therm. Efficiency steadily decreased throughout lactation. Efficiency ratios in the early part of lactation were abnormally high, due to catabolism of body fat. Least-squares analyses were carried out for 31- to 60-day, 121- to 150-day, and 181- to 210-day part-lactation efficiency, as well as for the total lactation. Generally, weight change during lactation, barns, weight, and parity had large effects on efficiency of production. The barn difference was found to be due to a bias in estimating forage consumption in one barn. The influences of days open, seasons, and years were relatively minor. Season effects were confounded with those due to weight change. It was concluded that heavier cows are less efficient in a biological sense, although this may be counteracted by their greater economies of scale in the use of labor and capital.