In order to estimate adjustment factors for effects of season and age of the dam on the litter size at farrowing and at weaning at 28 days in pigs, we analyzed 5457 farrowings from January, 1983, through September 1984 in three farms. Age had a significant effect on the variables (p 0.01). Season and the interactions had no effect (p 0.05). The results from the additive and multiplicative adjustment factors for age of dam were very similar, probably due to reduced size of such factors (no more than 8 %). Neverthless they had an effect on the variation coefficients. Farm affected litter size at weaning, but parity-farm interaction was not significant. Showing that in the three farms the age effect was similar, it was considered unnecesary to compute adjustment factors within farm.

R. R Navarro-Fierro, G. Guzman-Barcenas

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume X. Breeding programs for swine, poultry, and fish., , 182–186, 1986
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