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Genotype-Climatic and Other Interaction Effects for Productive Responses in Holsteins¹,^,2

Departments of Dairy Science and Experimental Statistics, Louisiana State University, Baton Rouge 70803

ABSTRACT

Season of calving had important effects on the shape of the lactation curve, affecting peak milk yield, persistency, and lactation lengths in a Louisiana Holstein herd. Feeding regime and age at calving also had marked effects. Plane of nutrition appeared to have more important effects on components of the lactation curve than did season of calving. Most interaction effects were small.

Lactation milk yield for Holstein cows in five Louisiana herds calving in the hot season of the year was consistently from 200 to 300 kg (5 to 8%) less than that for cows calving during cool and mild seasons. Yields during the first 90 days of lactation were 10 to 14% less.

Interactions of sire by season of calving for part and whole lactation milk and milk fat yields accounted for less than 1% of the total variance. Interactions of cow by season of calving were of the same general magnitude. Thus, genotype-climatic interactions for milk production for Holstein cattle under Louisiana conditions are not important enough to consider in the selective breeding program.

¹ Research supported in part by Hatch funds for Southern Regional Dairy Cattle Breeding Project(S-49).

² Part of the data for this paper is from a thesis submitted by the first junior author in partial fulfillment of the Master of Science degree in the Department of Dairy Science, Louisiana State University, Baton Rouge, 1972.