Use of group records of feed intake to select for feed efficiency in rabbit

Models for genetic evaluation of feed efficiency (FE) for animals housed in groups when they are either fed ad libitum (F) or on restricted (R) feeding were implemented. Definitions of FE on F included group records of feed intake ( $$ ) and individual records of growth rate (G_F ) and metabolic weight (M_F ). Growth rate (G_R ) as FE measurement on R was used. Data corresponded to 5,336 kits from a rabbit sire line, from 1,255 litters in 14 batches and 667 cages. A five-trait mixed model (also with metabolic weight on R, M_R ) was implemented including, for each trait, the systematic effects of batch, body weight at weaning, parity order and litter size; and the random effects of litter, additive genetic and individual. A Bayesian analysis was performed. Conditional traits such as $$ and $$ were obtained from elements of additive genetics ( $$ and $$ ) or phenotypic ( $$ and $$ ) (co)variance matrices. In the first case, heritabilities were low (0.07 and 0.06 for $$ and $$ , respectively) but null genetic correlation between the conditional and conditioning traits is guaranteed. In the second case, heritabilities were higher (0.22 and 0.16 for $$ and $$ , respectively) but the genetic correlation between $$ and $$ was moderate (0.58). Heritability of G_R was low (0.08). This trait was negatively correlated with $$ and $$ of animals on F, which indicate a different genetic background. The correlation between G_R and G_F was also low to moderate (0.48) and the additive variance of G_F was almost four times that of G_R , suggesting the presence of a substantial genotype by feeding regimen interaction.