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The Relative Importance of Heredity and Environment in the Growth of Pigs at Different Ages¹

Nebraska Agricultural Experiment Station and United States Department of Agriculture

Abstract

Data on 994 pigs were studied to observe the trends in the relative importance of hereditary and environmental agencies which affect weight and rate of gain from birth to 168 days of age.

Linear time trend over a 4-year period and season of farrowing (spring or fall) were unimportant sources of variation in weight. The large difference between periods in the same spring or fall season, closely associated with age, indicated that the responsible factors were environmental in origin and peculiar to each season.

The heredity of the pig played an increasingly important role in development from birth to 112 days. The genetic variance in rate of gain during relatively short intervals increased from 7 to 31 per cent. After 112 days the relative importance of heredity decreased considerably.

The relative importance of environment peculiar to the individual in determining rate of gain increased from 39 per cent at birth to 61 per cent at 168 days, the greatest increase being in the interval following weaning.

The relative influence of litter environment in determining rate of gain decreased from birth to 112 days, the greatest decrease being in the interval after weaning. An unaccountable increase occurred during the interval from 112 to 140 days.

The genetic variance in weight increased from zero per cent at birth to 28 per cent at 112 days. After 112 days, a decrease due to the lower heritability of gains in subsequent periods was noted.

The relative influence of environment peculiar to the individual in determining weight decreased from 51 per cent at birth to 34 per cent at 84 days, increasing thereafter to 51 per cent at 168 days.

The relative importance of litter environment in determining weight decreased regularly from 49 per cent at birth to 24 per cent at 168 days.

¹ Journal Series No. 305, Nebraska Agricultural Experiment Station in Cooperation with the Regional Swine Breeding Laboratory, Ames, Iowa, Bureau of Animal Industry, U. S. Department of Agriculture.

² Professor of Animal Husbandry, University of Nebraska (Lincoln, Nebr.), Agent in Animal Husbandry and Jr. Animal Husbandman, Bureau Animal Industry, U. S. Department of Agriculture (North Platte, Nebr.), respectively.