Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Animal Science


The beef cattle industry is one og the major sources of rural income in South Dakota. According to the South Dakota Crop and Livestock Reporting Services (1956), there were 1,492,000 beef cows and yearling beef heifers on the farms and ranches in South Dakota as of January 1, 1957. They also reported that sales from cattle and calves amounted to approximately 34.6 percent of the gross farm and ranch income in the state. Since the beef cattle industry is a major source of the farm and ranch income in South Dakota, any improvement in the performance of beef cattle will also improve the economy of the state. In part, most of the selection if beef replacement heifers has been based in breed type. As a result of this selection, improvement in type has occurred in the beef breeds. However, a comparable improvement in gaining ability does not seem to have occurred. Since the majority of the beef cattle are sold by weight, it appears that if should be a factor considered when selecting replacement heifers. The purpose of this study then is to obtain a workable selection method which the breeders would be able to adopt. According to Hazel and Lush (1942), the selection for a total score of index of set desirability is much more efficient than selection for one trait at a time. Before a selection index cane be constructed the heritability of each trait and the genetic correlations between the traits must be established. Therefore, reliable estimates need to be obtained for these genetic values. First, however, adjustments must be made for the sources of environmental and other variations that are known to account for some of the differences among animals. The sources if variation investigated here are the efforts of age on 18-month weight and the effects of inbreeding in weaning weight, 18-month weight and 18-month type score.

Library of Congress Subject Headings

Beef cattle
Beef cattle -- Breeding

Number of Pages



South Dakota State University

Included in

Beef Science Commons