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Selection for an Increase in Growth Rate and Market Score in Two Inbred Lines of Swine¹

Minnesota Agricultural Experiment Station

Abstract

The amount of selection, as measured by the average deviation of selected parents from their generation averages in score as to market desirability and growth rate (weight at 154 days of age), was determined in the Minnesota No. 1 and Minnesota No. 2, two inbred lines in the Minnesota swine breeding project. The average annual selection differentials for the No. 1 and No. 2, respectively, in score were 0.70 point and 0.60 point on the basis of 9 points being a perfect score. For weight at 154 days the selection differentials were 15.1 pounds and 10.2 pounds for the No. 1 and No. 2 respectively. The herd average scores for both lines were expected to increase when predicted from the selection differentials and the heritability estimates. That both lines showed some improvement was fairly evident from the time trends in herd average score. It was also predicted, using the selection differentials, heritability estimates for 154-day weights and rate of inbreeding, that the lines would show a decline in growth rate because the amount of selection practiced did not appear sufficient to offset the decline expected to result from the inbreeding carried on. The Minnesota No. 1 did decline in herd average 154-day weight, but the No. 2 appeared to be increasing slowly at a rate just less than 1 pound per year.

¹ Paper No. 2916, Scientific Journal Series of the Minnesota Agricultural Experiment Station in cooperation with the Regional Swine Breeding Laboratory, Ames, Iowa, Bureau of Animal Industry, U.S.D.A. This paper is condensed from a portion of a thesis submitted to the Graduate Faculty of the University of Minnesota in partial fulfillment of the requirements for the degree of doctor of philosophy.

² Formerly graduate student at the University of Minntsota, now Assistant Dean of Agriculture and Professor of Animal Husbandry at Texas Technological College.

³ Professor of Animal Husbandry at the University of Minnesota.