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Estimates of Genetic Parameters for Growth Rate and Backfat Thickness of Swine Tested to 105 and 135 Kg¹

Auburn University, AL 36849²

Abstract

A study involving 522 pigs sired by 68 purebred boars and out of 76 purebred sows of the Duroc and Landrace breeds was made to estimate the heritabilities of days required to reach 105 and 135 kg and backfat thickness at 105 and 135 kg, and the genetic correlations among these traits. The purebred boars and gilts were bi-directionally selected within breed and sex on the basis of days to 105 and 135 kg and backfat thickness at 105 and 135 kg and were mated assortatively to obtain crossbred progeny that were tested to 135 kg. The genetic parameters were determined by two methods: (1) regression of offspring's performance on midparent's performance and (2) the ratio of the selection response to the selection differential from one generation of divergent selection. Heritability estimates of days to 105 kg were .18 ± .09 and .22 ± .09; and heritability estimates of days to 135 kg were .35 ± .06 and .36 ± .08, respectively, for the two methods of estimation. The estimated genetic correlations between these two traits were .99 ± .00 and .94 ± .07, respectively. The heritabilities for backfat thickness at 105 kg were .79 ± .07 and .78 ± .09, respectively, and those for backfat thickness at 135 kg were .58 ± .06 and .65 ± .10, respectively. The estimated genetic correlations between these two traits were .88 ± .02 and .90 ± .04. These results indicate that swine should be tested to 135 kg to improve days to 105 kg, but only need to be tested to 105 kg to improve backfat thickness. There was evidence that the genetic correlations of days with backfat thickness estimated from the lines selected for days were different from the genetic correlations when estimated from the lines selected for backfat thickness.

¹ Contribution from the Alabama Agr. Exp. Sta., Journal Ser. No. 4-82305.

² Dept. of Anim. and Dairy Sci. Received October 12, 1982.

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