The aim of this study was to investigate if social genetic effects for average daily gain (ADG) in pigs depend on group size. Records included 119,919 pigs from 13 nucleus Landrace herds in Denmark. Pigs entered the performance test at 30 kg and were assigned to pens containing between 8 to 15 pigs. Each pen had approximately the same stocking density. A total of 10,803 groups of pigs were included. The ADG from 30 kg to the end of the test ( 94 kg) was 1012 g per day. ADG was analysed both separately for each of the eight different group sizes (8 to 15), and on the whole data, including all group sizes. Variance components were first estimated using a classical animal model including the fixed effect of sex, contemporary compartment, along with age and age squared at end of the test as covariates in addition to random effects of animal, group and litter. Thereafter variance components were estimated using a social genetic model, which in addition to the effects included in the classical model, included a social genetic effect. The social genetic variance for the eight different group sizes varied from 4.0±6.1 to 49.8±25. For the dataset including all group sizes, the social genetic variance was 9.1±2.1. For all group sizes, except group size 8, T2 (variance of the total breeding value relative to the phenotypic variance) was higher than the heritability estimated from the classical model. For the total dataset, T2 from the social model was 0.49±0.01, whereas the heritability from the classical model was 0.17±0.01. The direct-social genetic correlations were not significantly different from zero. In conclusion, significant social genetic effects were found for most group sizes. However, we did not find that estimates of social genetic effects for ADG depended on group size in a systematic way. Keywords: pig, social genetic effects, group size, daily gain

Hanne Marie Nielsen, Birgitte Ask, Ole Fredslund Christensen, Luc Janss, Marzieh Heidaritabar, Per Madsen

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume Biology - Behaviour, , 212, 2018
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