Genetic response on postweaning growth performance in three lines of meat rabbit selected for feed efficiency using alternative criteria.

Improving feed efficiency is a major goal in rabbit production, as feed costs account for over 60% of total expenses. This study evaluated the genetic responses of three group-housed rabbit lines selected according to alternative criteria for feed efficiency, all of which accounted for social interaction effects: average daily gain under feed restriction (ADGR), cage-level residual feed intake under ad libitum feeding (GRP) and individual residual feed intake under ad libitum feeding (RFI). The control population (X) originated from vitrified embryos of the base population (the Caldes line after four generations of mating without selection), from which the selection lines were established. After seven generations, 3 083 animals were evaluated under three feeding systems (conventional, electronic, and individual cages). BW was recorded at 38 and 58 days, and feed intake was monitored during the control period. Data were analysed using a multivariate Bayesian approach, and genetic responses were estimated by comparing selected lines with the control. Results showed clear differences across criteria: GRP rabbits consistently consumed less feed (-13.7 to -17.8 g/d; marginal posterior probability of being greater than zero, Pr(>0) = 0) and grew more slowly (-3.5 to -3.9 g/d; Pr(>0) = 0); nevertheless, they achieved improved efficiency, with the strongest effect under electronic feeders (ΔFCR = -0.15; Pr(>0) = 0). RFI rabbits also reduced intake (-4.6 g/d; Pr(>0) = 0.03) with electronic feeders) and growth (-1.2 g/d; Pr(>0) = 0.05); however, this did not result in a significant improvement in feed conversion ratio. ADGR rabbits showed less consistent outcomes, with slightly higher growth under conventional feeding (+0.76 g/d; Pr(>0) = 0.91) but higher feed intake (+9.7 g/d; Pr(>0) = 1), leading to a deterioration in the feed conversion ratio (+0.15 g/g; Pr(>0) = 0.98). Records from individually housed animals were less informative due to a smaller sample size. Overall, the GRP criterion emerged as the most promising strategy, reducing feed intake and improving efficiency, although at the expense of growth. Electronic feeders were essential for accurate intake recording in group housing and better reflected commercial conditions than individual cages. In conclusion, alternative selection criteria produced distinct genetic responses, with GRP selection offering the greatest potential to enhance efficiency and sustainability in rabbit production systems.