Using Pedigree data in order to study genetic variability in the French Large White, Landrace and Pietrain pig breeds

Pedigree data, collected in the French Large White (LW), Landrace (LR) and Pietrain (PI) breeds between 1962 and 1996, were used to study recent changes of the genetic variability in these 3 breeds. Pedigrees appeared to be well known in the LW and LR (more than 50 % of known ancestors of rank 10), at a lesser extent in the PI because of imports. The length of generation remained the same in the 3 breeds on the maternal path (21 to 24 months), wheras it increased with the use of Artificial Insemination (AI) on the paternal path, up to 20 to 25 months.The number of founders was estimated by different methods. They all showed that the LW has a fairly large basis (n = 113 effective founders) ; the PI showed a similar situation (n = 78) in spite of the small population size, thanks to imports; the LR showed the smallest basis (n = 55), having passed through two successive bottlenecks in the last decade, first when the Hal gene was eradicated, then when the hyperprolific line was developped. The hyperprolific programme led to a clear decrease in the number of effective founders, in both LW and LR, between 1990 and 1995.Among the other results, the rate of inbreeding remained at a low level (2 to 3 % in the 3 breeds in 1996), although it increased in the recent years, especially in the LF where 33 % of the animals had a rate of inbreeding higher than 1/32.As a conclusion, the use of AI boars with high genetic value in the selection tier should be put a limit in order to avoid a decrease of genetic variability ; otherwise, such a decrease might happen quickly in selected pig populations.