Genetic Trend of Growth Rate and Backfat Thickness of Swine in Ontario1

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Abstract
On-farm and central test station records of Yorkshire (Y), Landrace (L), Hampshire (H) and Duroc (D) swine born between 1976 and 1983 were used to estimate genetic trend in age to 90 kg (d) and backfat thickness (mm) adjusted to 90 kg. Multiplicative factors adjusted both traits for sex of pig. The within breed, single trait model included effects of fixed herd-year-season (hys) of birth, random litter within hys, random breeding value of pig within litter, and residual. Genetic trend was estimated by linear regression of mean predicted breeding value on year or year-season of birth. Trends in age (d/yr) of pigs born July, 1981 to December, 1983 were Y, −.54; L, −.82; H, −.52; D, −.62. Trends in backfat (mm/yr) were Y, −.12; L, −.18; H, −.02; D, −.02. Trends of parents (average of boars and sows) born 1974 to 1982 for age were Y, −.36; L, −.43, H, −.33; D, −.15 and for backfat Y, −.11; L, −.14; H, −.04; D, −.05. Trends were greater for boars than for sows in all breeds and for both traits. Copyright © 1985. American Society of Animal Science. Copyright 1985 by American Society of Animal Science

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