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Performance of Inbred Lines and Line Crosses of Holsteins for Body Growth¹

Departments of Dairy Science and Genetics, University of Wisconsin, Madison 53706

ABSTRACT

Estimates of the effects of inbreeding and outbreeding in dairy cattle were made in an experiment designed specifically to study these effects in a population in which no artificial selection was practiced. The basic groups in this study were 6 unrelated lines of Holstein cattle; each line was based on a foundation stock of 1 sire, 1 or 2 inbred sons and 20 noninbred daughters. Animals were mated within each line and between lines to produce inbred and "out-bred" progeny, respectively. Further outbreeding was conducted by crossing the inbred animals from different lines to produce 2-, 3-, and 4-line crosses. Only a fraction of the total posssible crosses was made. Significant (P < .01) differences were found for body measurements at birth, 3, 6, 12 and 18 months of age, and at 3 months after first calving between the inbreds and "outbreds" when both were from noninbred dams, and between the inbreds and 2-line crosses when both were from inbred dams. The 2-line crosses were significantly superior to the "outbreds." The inbred females from inbred dams averaged below the inbreds from noninbred dams at birth for all body measurements; but these differences were reversed at older ages. The average body measurements of the animals in the 2-line, 3-line, and 4-line cross mating systems were similar.

¹ From the Laboratory of Genetics (Paper no. 1162) and Department of Dairy Science; published with the approval of the Director of the Agricultural Experiment Station. Contribution from the Wisconsin Agricultural Experiment Station as a collaborator under the North Central Region Cooperative Research Project entitled Improvement of Dairy Cattle Through Breeding—NC-2, conducted in cooperation with the Dairy Cattle Research Branch, USDA.

² Université Laval, Department of Animal Science, Quebec, Canada.