Changes of EBV trajectories for feed conversion ratio of growing pigs due to divergent selection for residual feed intake

The objective of this paper was to study the estimated breeding values (EBV) profiles for feed conversion ratio (FCR) over the growing period in eight generations of divergent selection for Residual Feed Intake (RFI) in Large White pigs. Data comprised 11790 weekly FCR collected on 1186 boars during a 10 week-period. A random regression model was used to estimate 10 week EBVs per animal. Then, the individual EBV trajectories were classified into subgroups using a k-means approach with a Euclidean distance. The responses to selection in the divergent lines (LRFI= low RFI; HRFI= high RFI) on the FCR dynamics were evaluated. On the one hand, the average weekly EBV over time per line and generation were considered; on the other hand the first two summarized breeding values (SBV1 & SBV2, representing the slope and the mean of the EBV curves, respectively) were computed for each individual from the eigendecomposition of the genetic covariance matrix between time points, and they were averaged for each line and generation. The results showed that individual EBV trajectories for FCR were classified into three distinct subgroups. These groups corresponded to early generations, late LRFI generations, and late HRFI generations, respectively. The more efficient pigs had smaller initial value of FCR and smaller slope of the EBV than less efficient pigs. The changes in SBV1 and SBV2 corroborated the evolution of the EBV curves for each line and generation. Further examination pointed out changes in the dynamics of growth rates associated to these responses. This study showed that selection for feed efficiency affected the dynamics of FCR during growth.