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Sources of Variation in Quarter Milk Flow Measures^{1 ,2,}

Department of Dairy Science, University of Maryland, College Park 20742
and Animal Science Institute, SEA-AR, USDA, Beltsville Agricultural Research Center, Beltsville, MD 20705

ABSTRACT

An individual quarter milker was used to measure milk yields at staggered 20-s intervals from 198 Holstein cows in the Beltsville Agricultural Research Center herd. Several flow rate variables were calculated. The 2792 quarter samples of milk yield were taken during afternoon milkings. Yields and rates of individual quarters were examined as were effects of lactation, stage of lactation, machine, and cow. Differences between rear and front quarters were .78 kg for yield and .12 kg/min for maximum rate. Differences between left and right quarters were .02 kg/min for maximum rate and .10 kg for yield during the period of maximum rate. Yields departed from front-rear and left-right side patterns. This lack of symmetry, interactions of front-rear by side, for the yield traits may have been from permanent environmental causes such as developmental error, mastitis, or injury. Cow effects were important for all traits as were the effects of lactation, stage of lactation, and machine for many of the traits. Repeatabilities were .63 for maximum rate and .60 for average rate. Designers of milking machines may wish to account for differences between quarters in newer milking machines.

¹ Scientific Article No. A2707, Contribution No. 5752 of the Maryland Agricultural Experiment Station, Department of Dairy Science.

² Work in Cooperation with Animal Science Institute, SEA-AR, USDA, Beltsville Agricultural Research Center.

³ Department of Animal Science, Iowa State University, Ames 50011.

⁴ Westat, Inc. Rockville, MD.

⁵ Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061.

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