A field enquiry mentioned the potential positive impact of a feed restriction on the health of young rabbits, but no objective information relates the intake to digestive health. The effects of a post-weaning feed restriction strategy were thus studied on digestive health and growth and carcass parameters of the growing rabbit, using a monofactorial design that produces a quantitative linear reduction of the intake, from ad libitum (AL group) to 80%, 70% and 60% of AL. The study was performed simultaneously in six experimental sites, on 1984 growing rabbits (496 per treatment) collectively caged from weaning (34 to 38 days of age, depending on the site) to slaughter (68 to 72 days). The feeding programme was applied as followed: restriction during 21 days after weaning, and then ad libitum till slaughter. During the feed restriction period the growth rate was linearly reduced with the restriction level, by 0.5 g/day for each percent of intake reduction. When returning to ad libitum intake (after 54 days old) a compensatory growth and a higher feed efficiency occurred. Therefore, the impact of the feeding programme on the slaughter weight (SW) was significant (24.5 g/% of restriction), but relatively moderate: the weight loss of the more-restricted rabbits (60%) reached 7.7% (2200 g) compared to the AL group. Over the whole fattening period, the feed restriction reduced linearly and significantly the feed conversion (FC) (20.0077 unit/% of restriction). Carcass traits were little affected by the feeding programme, except for a slightly lower decrease of the dressing percentage (mean: 1.2 units between AL and the three restricted groups). On the six experimental sites, mortality and morbidity were always caused by acute digestive disorders, namely diarrhoea and/or caecal impaction. Independent of the treatment, the mortality rate strongly varied according to the site (between 7% and 18% from weaning to 54 days and for the AL group). During feed restriction, the mortality was significantly lower from a restriction threshold of 80% (meanly: 29% compared to AL). The morbidity was also significantly reduced (26%) for the two most restricted groups (70% and 60%). The favourable effect of a lower intake on health did not persist after returning to ad libitum intake (54 days to slaughter), since mortality and morbidity were not significantly different among the treatments. Such a feeding strategy thus represents a double benefit in terms of feed costs and lower losses of young rabbits.

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-The effects of the level of dietary starch on growth performance and mortality were studied in six experimental sites on 2 328 growing rabbits (582 per diet). Four iso-lignocellulosic (ADF) diets (A12, A16, A20, A24) with increasing starch content (12, 16, 20, 24%) instead of digestible fibre (hemicelluloses and pectins) were compared. Diets were given ad libitum from weaning (28 and 35 d old, depending on the site) to slaughter (between 68 and 71 d old). The increase (12 points) of dietary starch level led to a double-rise of mortality rate by digestive disturbances: 4.6% and 10.1% respectively for A12 and A24 for the whole period. In parallel, the feed conversion ratio decreased slightly but significantly by 0.15 point between A12 and A24. The feed intake and the digestible energy intake was respectively reduced by only 4.5% and by 1.5% (P < 0.01), between the A12 and A24 diets. During the whole period the growth rate remained similar for the four diets (mean = 42.5 g . d -1 ). To ensure digestive security of the growing rabbit, it is recommended to maintain a dietary starch level below 14% during the post-weaning period, while for the end-fattening period dietary starch could reach 18%. rabbit / feeding / starch / fibre / growth / diarrhoea / mortality

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Four diets were arranged using a 2 ✕ 2 factorial design with two levels of lignocellulose, a high ‘HF’ or a low level ‘LF’ (acid-detergent fibre (ADF) = 191 v. 155 g/kg), combined with two levels of starch replacing 50 g/kg of digestible fibre (DF = hemicelluloses + pectins), a high starch (low DF) ‘HS’ or a low starch (high DF) level ‘LS’ (starch = 193 v. 123 g/kg). Two trials were conducted to measure digestive efficiency and rate of passage, respectively. A third trial was performed in a network of six French experimental breeding units to measure growth and digestive health on 507 rabbits per diet. Foods were offered ad libitum from weaning to slaughter.No significant interactions were detected between the effect of the level of lignocellulose and the effect of starch replacement by DF, on rabbit digestion, performance or digestive health. A proportional increase of overall food digestibility (organic matter (OM) or energy) was observed with the decrease of ADF level. When 50 g/kg of DF was replaced by starch we observed a significant improvement of OM and energy digestibility ( + 0·03 units). The whole-tract mean retention time of particles was 21 h. It was significantly longer with a lower ADF level ( + 5·4 h for LF v. HF diets), and it tended to increase when DF was substituted by starch ( + 2·2 h for HS v. LS diets).Between weaning and slaughter, food intake was mainly affected by the ADF level (139 v. 130 g/day respectively for HF and LF diets) and to a lesser extent by the replacement of DF by starch (136·2 v. 133·4 g/day, respectively for LS and HS diets). The weight gain was only slightly higher for high starch (low DF) diets ( +1 g/day) without an effect of the ADF level.Between weaning and slaughter, morbidity and mortality rates (from acute diarrhoea) were significantly reduced with high-fibre diets (-6 and -4 units respectively), while the replacement of DF by starch had no significant effect.

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These results demonstrated that, in rabbits, restriction and, to a lesser extent, dietary energy concentration modulate gut immunity.