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Selection fo Lean Growth in Swine¹

University of Nebraska³, Lincoln 68583

Abstract

Growth rate (ADG) and backfat (BF) data were collected during five generations of selection in two lines of Gene Pool pigs (14-breed synthetic): select (S) and control (C). C were randomly selected, while mass selection was practiced in the S line with an index (I), I = 100 + 286.6 (ADG) — 39.4 (BF). S and C pigs were fed a 14% protein, corn-soybean meal diet from 42 d of age until they reached 79.4 kg. The ratio of weighted to unweighted selection differentials offers evidence that natural selection was not working against artificial selection. Weighted cumulative selection differentials (adjusted for any unintentional selection occurring in the C line) were .40 kg ADG, —.70 cm BF and 143 I units. The regressions of response (S—C) on generation number were .014 ± .002 kg ADG, —.045 ± .010 cm BF and 5.76 ± .30 I units. The realized response was 41 and 38% of the expected response for ADG and BF, respectively. Realized heritability estimate for the I was .19 ± .029. The index in retrospect indicated that other factors such as natural selection and management had little effect on the selection criteria. Index selection was effective in improving both ADG and BF.

¹ Published as Paper No. 6041 Journal Ser., Nebraska Agr. Exp. Sta.

² Present address: Rural Development Center, Tifton, GA 31793.

³ Dept. of Anim. Sci.