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Genetic and Maternal Effects on Pig Weights, Growth and Probe Backfat in Diallel Crosses of High- and Low-Fat Lines of Swine¹

U.S. Department of Agriculture^,4, Beltsville, MD 20705

Abstract

Two Duroc and two Yorkshire lines of pigs that had been selected at Beltsville Agricultural Research Center for 12 and 10 generations, respectively, for either thinner or thicker backfat were mated to produce all possible pure lines and reciprocal crosses in 1967, 1969 and 1970. Data for littermate gilts and barrows from 136 litters were analyzed to estimate genetic and maternal influence on individual pig weights at birth, 21 d, 56 d and 140 d of age; age at 79.4 kg; average backfat thickness at 79.4 kg and postweaning average daily gain (56 d to 79.4 kg). Pure-line gilts differed among breed-lines (P<.05 or P<.01) for all traits except weight at 56 d. Gilts of the two low-fat lines were heavier than gilts of the two high-fat lines through 56 d of age, but Yorkshire low-fat gilts were lightest at 140 d, were oldest at 79.4 kg and had the slowest daily gain, in addition to the least backfat. The Duroc low-fat line gilts were heaviest at 140 d, youngest at 79.4 kg and were second thinnest in backfat. Among pure-line barrows, the low-fat lines were heaviest at birth, at 21 d and at 140 d and were thinnest in backfat. Line-cross gilts were heavier than pure-line gilts at all four ages, were younger at 79.4 kg and higher in daily gain. Among barrows, line crosses were heavier in all weights except at 21 d, were younger at 79.4 kg and were higher in daily gain than pure lines. Differences between pure lines and line crosses in backfat were not significant for either sex. Heterosis varied from 6.5 to 16.7% among weights and growth traits. Pigs of both sexes differed among breed-lines in general combining ability for all traits except 21-d weight, and differed in maternal ability for weights through 56 d and for backfat. Specific combining ability (SCA) was significant only for intra-breed crosses for weight at 21 d, and for inter-breed, intra-line crosses for 21- and 56-d weights and for age at 79.4 kg among gilts, with no significant effects in SCA for any trait among barrows. General combining ability was not correlated with maternal effects for any trait except 21-d weight, for which they were positively correlated (r>.80).

¹ The authors acknowledge with appreciation the contributions of W. H. Peters, Head, Animal Operations, for managing the swine herd and recording the necessary performance data during this experiment; the contributions of Bonnie Morgan, Statistical Assistant; and the comments by Dr. D. L. Kuhlers, Auburn Univ., and by Dr. L. D. Young, Roman L. Hruska U.S. MARC, Clay Center, NE.

² USDA, Agr. Res. Serv., BeltsviUe Agr. Res. Center, Animal Sci. Inst., Nonruminant Anim. Nutr. Lab., Beltsville, MD 20705.

³ USDA, Agr. Res. Serv., Beltsville Agr. Res. Center, Beltsville, MD 20705, retired.

⁴ Mention of trade name, proprietary product or vendor does not constitute a guarantee or warranty of the product by USDA or imply its approval to the exclusion of other products or vendors that may also be suitable.