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Crossbred and Purebred Dairy Cattle in Warm and Cool Seasons^1,2,

Department of Animal Science, North Carolina State University, Raleigh 27650

R. E. McDowell⁴

Animal Physiology and Genetics Institute, USDA, Beltsville, MD 20705

J. C. Johnson, Jr.

University of Georgia, Coastal Plain Experiment Station, Tifton 31794

B. T. Hollon⁵

Iberia Livestock Experiment Station, Jeanerette, LA 70544

G. W. Brandt

Department of Dairy Science, Clemson University, Clemson, SC 29631

ABSTRACT

This study was to determine if breed groups ranked differently in warm (May to August) and cool (November to February) seasons of calving and to determine if heterosis was more important in the warm season. A total of 719 records of cows in first lactation in four herds in the southeastern United States were used. Breeds were Holsteins, Brown Swiss, and Jerseys and the crosses among them. Milk and milk fat yields were greater in the cool season than in the warm season. Holsteins exceeded other breeds for milk and milk fat yield in both seasons, but their superiority was less among cows calving from May through August. Days open were longer for Holsteins, particularly in the warm season. In the cool season only the Holstein x Swiss group exceeded Holsteins for milk, but two groups — Holsteins x Swiss and Holstein x Swiss- Jersey — were higher in the warm season. In the cool season three crossbred groups — 1) Holstein x Swiss (Holstein sires), 2) Holstein x Swiss, and 3) Holstein x Swiss- Jersey — had greater milk fat yields than Holsteins, and a fourth — Holstein x Jersey — yielded an equal amount. In the warm season six of the eight crossbred groups had greater milk fat yields than Holsteins. More crossbreds exceeded Holsteins in the warm than in the cool season, suggesting interactions for yields. There was slightly more heterosis in warm than in cool seasons for all traits.

¹ Paper No. 8241 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh.

² This work was part of the Southern Regional Dairy Cattle Breeding Project, S-49 (Genetic Methods of Improving Dairy Cattle for the South.)

³ SR-CRSP, PO Box 58137, Nairobi, Kenya, East Africa.

⁴ Dept. Animal Science, Cornell University, Ithaca, NY 14850.

⁵ Dairy Experiment Station, Lewisburg, TN 37091.