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Effectiveness of Selecting for Rapid and for Slow Growth Rate in Hampshire Swine¹

University of Illinois

Abstract

SWINE breeders have been influenced, consciously or unconsciously, by growth rate in attempting to improve their hogs. This attention to growth rate is justified by the shorter feeding period and by the smaller feed requirement generally associated with an increase in growth rate. The effectiveness of such selection depends largely upon the extent to which the observed differences in growth rate are actually heritable, in the sense that the offspring will exhibit part of the superiority or inferiority in growth rate which their parents exhibited. Many estimates of heritability have been made from studies of the association between growth rates of parents and their offspring. In certain breeding experiments with both plants and animals the actual cumulative effects of selection over a number of generations have been measured to determine how much of the change resulting from selection is permanent.A classic selection experiment of this kind is the one on the composition of corn conducted by Winter (1929) and analyzed further by "Student" (1934). Similar studies have been reported for egg production in poultry by Marble and Hall (1931), for body size in mice by Goodale (1938) and by MacArthur (1944), for food consumption and utilization in the rat by Morris et al. (1933), and for feed utilization in swine by Grimes (1941).

¹ This investigation was conducted in cooperation with the Regional Swine Breeding Laboratory, Ames, Iowa, Bureau of Animal Industry, U. S. Department of Agriculture.

² We gratefully acknowledge the assistance and excellent suggestions of Dr. G. E. Dickerson, Geneticist, Regional Swine Breeding Laboratory. We are also indebted to Miss M. E. Gregory for assistance in the statistical analysis of the data, and to R. H. McDade, Chief Swine Herdsman, whose interest at the farm added materially to the experiment.