Estimation of realised genetic trends in French Large White pigs from 1977 to 1998 using stored frozen semen : experimental design and first results

An experimental design has been implemented in order to estimate realised genetic trends from 1977 to 1998 in the French Large White pig breed. Large White sows were inseminated with stored frozen semen of boars born in 1977 or with semen of boars born in 1998, producing 30 and 33 litters, respectively. Progeny (197 individuals from litters from 1977 and 244 individuals from litters from 1998) were tested for growth, fatness and male sexual development traits.The results showed a highly significant genetic progress in backfat thickness (-0.24 ± 0.03 mm per year for average backfat thickness measured on 22-week-old animals). No significant change was found in birth weight and growth before weaning. The results for average daily gain from 22 to 26 weeks of age showed a significant annual increase of 7.7 ± 2.1 g/j, but no clear trend appeared for growth during the commercial fattening period (10-22 weeks of age).Testis width did not differ at 14, 18 and 26 weeks of age, but was significantly larger at 22 weeks of age for 1998 sires offspring (+0.47 ± 0.14 mm per year), showing an earlier testis development. No difference was found in bulbo-urethral gland size measured on 22- and 26-week-old individuals.