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 ( FI ¯ F ) and individual records of growth rate (GF ) and metabolic weight (MF ). Growth rate (GR ) 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, MR ) 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 FI ¯ F | M F , G F and G F | M F , FI ¯ F were obtained from elements of additive genetics ( FI ¯ F | M F , G F g and G F | M F , FI ¯ F g ) or phenotypic ( FI ¯ F | M F , G F p and G F | M F , FI ¯ F p ) (co)variance matrices. In the first case, heritabilities were low (0.07 and 0.06 for FI ¯ F | M F , G F g and G F | M F , FI ¯ F g , 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 FI ¯ F | M F , G F p and G F | M F , FI ¯ F p , respectively) but the genetic correlation between FI ¯ F | M F , G F p and G F was moderate (0.58). Heritability of GR was low (0.08). This trait was negatively correlated with G F | M F , FI ¯ F p and G F | M F , FI ¯ F g of animals on F, which indicate a different genetic background. The correlation between GR and GF was also low to moderate (0.48) and the additive variance of GF was almost four times that of GR , suggesting the presence of a substantial genotype by feeding regimen interaction.