GENETIC CORRELATIONS BETWEEN PRODUCTION AND REPRODUCTIVE TRAITS MEASURED ON THE FARM, IN THE LARGE WHITE AND FRENCH LANDRACE PIG BREEDS

The genetic correlations between production and reproductive traits me asured on the farm in the Large White and French Landrace pig breeds w ere estimated using a restricted maximum-likelihood procedure applied to a multiple-trait animal model. Two production traits, the age at 10 0 kg liveweight (A100) and the average backfat thickness adjusted at 1 00 kg (B100), as well as six reproductive traits, the total number of piglets born (TNB) or born alive (NBA) per litter considering all litt ers, only the first litter (TNB1 and NBA1), or only the second litter (TNB2 and NBA2), have been analysed. Data on 41 085 and 40 405 litters , and production traits measured on 29 607 and 25 283 gilts, in the La rge White and French Landrace breeds, respectively, were used. The est imated genetic correlations between B100 and the reproductive traits w ere close to zero or slightly unfavourable (from -0.02 to 0.10) and id entical in the two breeds. A stronger genetic antagonism was estimated between A100 and the reproductive traits, especially in the Large Whi te breed for traits TNB and NBA (genetic correlations were 0.15 and 0. 24, respectively). In the French Landrace breed, the estimated genetic correlations between A100 and the total number of piglets born, or bo rn alive, were stronger when considering the first or the second litte rs, than when considering those of higher parities. The low genetic op position between the two groups of traits estimated in this study may be considered to slightly decrease the efficiency of selection program mes.