Feed restriction strategies in growing rabbits fed post-weaning diets with different protein levels

The present study evaluated the effects of the feeding system (AL: ad libitum vs. R1: monophasic feed restriction vs. R2: biphasic feed restriction) and the dietary crude protein (CP) level (HP: 16% CP vs. LP: 14% CP) on growth performance and slaughter yield of 336 crossbred growing rabbits reared from weaning to slaughtering (33–78 d of age) in 48 collective pens (7 rabbits/pen; 8 pen/group). The access time to feeders decreased from 16 to 9 h/d in the first week of trial in both R groups; it was 8 h/d given in a single slot (R1 group) or in two slots (R2 group: 4 h + 4 h separated by 4 h without feed access) during the 2nd and 3rd week. Then, access time increased to 12 h/d during the 4th week and, thereafter, it was 12 h/d in a single slot of access for both R groups until the end of the trial. The HP and LP diets were administered from 33 to 60 d of age, then the same fattening diet (14% CP) was provided to all groups. Data were analysed by ANOVA using PROC GLM procedure of SAS software. In the first period (33–61 d), both R groups showed lower daily weight gain (DWG) and feed intake (DFI) and better feed conversion (FC) compared to AL group (p < 0.001). In the second period (61–78 d), R rabbits maintained a lower DFI (p = 0.02) compared to AL rabbits but showed a higher DWG (p < 0.001) and a better FC (p < 0.001). At the end of the trial, there were no differences on growth performance among groups, whereas both R systems improved FC compared to AL one (p < 0.001). The R2 group had better FC than R1 during the 2nd and 3rd week. However, the differences between R1 and R2 groups disappeared in the following weeks- with the return to the monophasic system. At slaughtering, R rabbits had decreased carcass yield (p < 0.001) compared to the AL ones. The use of LP diet decreased DWG (p < 0.001) and increased FC (p < 0.001) in the first period. However, in the second period, LP rabbits achieved a higher DWG (p = 0.01) and a better FC (p = 0.01) compared to HP rabbits. At the end of the trial, LP and HP rabbits showed similar growth performance and slaughter results. Finally, no significant interaction was found between feeding system and dietary protein level. In conclusion, the application of feed restriction systems improved rabbit feed efficiency but significantly decreased slaughter yield compared to the AL system. The dietary CP level can be reduced until 14% in the post-weaning diets without negative effects on growth performance and slaughter yield.