Abstract
Five generations of selection for improved feed efficiency (feed/gain) were practiced from 1971 to 1976. Performance records were collected on 642 Yorkshire boars from 135 sires and 345 dams. All boars were individually fed ad libitum to 100 kilograms. Responses to selection were estimated by the regression of generation means adjusted for environmental effects on generation number. The regression of adjusted feed efficiency means on generation number was −.019 ± .025. The realized heritability of feed efficiency was .09 ± .08. Correlated responses to selection for rate of gain, daily feed consumption, backfat thickness and subjective feed wastage and pen cleanliness scores were estimated by the regression of generation means adjusted for environmental effects on generation number. The regression coefficients were .003 ± .018 for rate of gain, −.007 ± .029 for daily feed consumption, −.003 ± .022 for backfat thickness, −.021 ± .052 for feed wastage score and −.032 ± .037 for pen cleanliness score. None of the regression coefficients was significantly different from zero.
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