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) over bar (F)) 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 (FI) over bar (F)vertical bar M-F,G(F)and G(F)vertical bar M-F,(FI) over bar (F) were obtained from elements of additive genetics ((FI) over bar (F)vertical bar M-F,G(F))(g) and ((G(F)vertical bar M-F,(FI) over bar (F))(g)) or phenotypic ((FI)over bar>(F)vertical bar M-F,G(F))(p) and (G(F)vertical bar M-F,(FI) over bar (F))(p)) (co)variance matrices. In the first case, heritabilities were low (0.07 and 0.06 for ((FI)over bar>(F)vertical bar M-F,G(F))(g)and (G(F)vertical bar M-F,(FI) over bar (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)over bar>(F)vertical bar M-F,G(F))p and (G(F)vertical bar M-F,(FI) over bar (F))(p), respectively) but the genetic correlation between (FI)over bar>(F)vertical bar M-F,G(F))p and G Fwas moderate (0.58). Heritability of GR was low (0.08). This trait was negatively correlated with (G(F)vertical bar M-F,(FI) over bar (F))(p) and (G(F)vertical bar M-F,(FI) over bar (F))(g) 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 GF was almost four times that of G(R), suggesting the presence of a substantial genotype by feeding regimen interaction.