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The importance of dietary fibre fractions in animal feeding is due to its influence on the rate of passage, mucosal functionality and its role as substrate for gut microbiota that relates to performance and digestive health. The complexity of the physical structure and chemical composition of polysaccharides in plant cell walls explains the wide and different physiological effects of this large range of fibre fractions. Our review will first briefly consider the definition and structure of the different classes of fibres and of cell wall constituents, followed by a description of some analytical methods employed for monogastric feeds. Second, the nutritional role and impact of fibre intake on digestive health will be described for the growing rabbit with an extensive analysis of previous studies performed without antibiotics. The fibres in rabbit feed are essential for reducing the risk of digestive trouble after weaning, and the requirements are defined in terms of the quantity and quality of the fibre fractions as follows: a minimal dietary level of lignocellulose ‘ADF’ (18%) and lignins (>5%), balanced with a maximum quantity of digestible fibres ‘DgF’ (ratio DgF/ADF below 1.3). Soluble fibres, defined as the difference between total dietary fibre and NDF, are quickly fermented and digested by the rabbit. However, their impact on digestive health is still questioned.

This review aims to present the different effects produced by a post-weaning intake limitation strategy on the growing rabbit, now largely used by French professional rabbit breeders. Although a quantitative feed restriction leads to slower growth, feed conversion (FC) is improved, particularly when the rabbits are again fed freely, as compensatory growth occurs. This better FC or the healthy rabbit is because of better digestion resulting from slower passage through the intestine, whereas the digestive physiology is slightly modified (morphometry of the intestinal mucosa, fermentation pattern, microbiota). Meat quality and carcass characteristics are not greatly affected by feed restriction, except for a lower dressing-out percentage. One of the main advantages of limiting post-weaning intake of the rabbit is to reduce the mortality and morbidity rate due to digestive disorders (particularly epizootic rabbit enteropathy syndrome). The consequences for animal welfare are debatable, as feed restriction probably leads to hunger, but it reduces the incidence of digestive troubles after weaning. However, the growing rabbit adapts very well to an intake limitation strategy, without any aggressive behaviour for congener. In conclusion, restriction strategies could improve profitability of rabbit breeding, but they should be adapted to any specific breeding situation, according to the national market, feed prices, etc.

In rabbits, the bacterial and archaeal community of caecal ecosystem is composed mostly of species not yet described and very specific to that species. In mammals, the digestive ecosystem plays important physiological roles: hydrolysis and fermentation of nutrients, immune system regulation, angiogenesis, gut development and acting as a barrier against pathogens. Understanding the functioning of the digestive ecosystem and how to control its functional and specific diversity is a priority, as this could provide new strategies to improve the resistance of the young rabbit to digestive disorders and improve feed efficiency. This review first recalls some facts about the specificity of rabbit digestive microbiota composition in the main fermentation compartment, and its variability with some new insights based on recent molecular approaches. The main functions of the digestive microbiota will then be explained. Finally, some possible ways to control rabbit caecal microbiota will be proposed and a suitable timing for action will be defined.

Alternative strategies to synthetic chemical drugs are needed in livestock and are a key issue in organic farming today. This study aimed at examining the potentialities of sainfoin, a legume rich in condensed tannins, as a nutraceutical that combines nutritive and antiparasitic effects in rabbits. To test the effect of infection with a helminth (I: infected groups; NI: not infected groups) and the effect of substituting 40% of the alfalfa in a control diet (C) with sainfoin (diet S), four groups of 16 weaned rabbits were arranged according to a 2×2 bifactorial design. The sainfoin diet differed from the control by its tannin concentration (1.8% v. 1.0% tannic acid equivalent) and its ADL concentration (84 v. 43 g/kg). For each diet, 16 rabbits were infected with 2125 third-stage larvae of Trichostrongylus colubriformis. Growth, feed intake, feed conversion ratio and nematode faecal egg counts (FECs) were controlled for 6 weeks. A digestibility trial was performed. After necropsy, adult worms and eggs in utero per female were counted and egg-hatching rate calculated. Growth tended to be lower for S groups than for C groups (38.2 v. 39.5 g/day; P=0.06). Feed intake was higher for S groups compared with C groups (+5.2 g dry matter/day; P<0.01), as was the feed conversion ratio (3.2 v. 2.9; P<0.001), probably in relation to the dietary ADL level. Protein digestibility was reduced in S groups compared with C groups (−6.0 points; P<0.001), probably associated with the effect of the tannin concentration. Digestibility of hemicelluloses was reduced in infected rabbits compared with non-infected ones (−5 points; P=0.01). Using the substitution method, the digestible energy of dehydrated sainfoin pellets used as raw material was calculated at 11.12 MJ/kg and digestible proteins at 110 g/kg. The infection did not produce any clinical signs of digestive disorders. No differences were observed according to the diet, neither in the number of adult worms (972; P=0.50), the number of eggs in utero per female (14; P=0.95), nor FEC (400 eggs/g; P=0.57). In contrast, the rate of faecal egg hatching in the S group tended to be lower than in the control (58.3% v. 85.2%; P=0.08). In conclusion, sainfoin seems to fit nutritive requirements for rabbits, supplies a large quantity of fibre and particularly lignins, and limits the development of nematode eggs in faeces.

Feed restriction could be a relevant strategy to preserve gut health, reduce systemic inflammatory response and finally limit antibiotic use. This study assessed the effect of feed restriction on growing pigs submitted to a moderate inflammatory challenge induced by the degradation of the environmental hygiene that is known to alter growth rate. The experiment was run on 80 pigs selected at 7 weeks of age according to a 2×2 factorial design: two feeding levels, ad libitum (AL) and feed restricted (FR) at 60% of AL, and two conditions of environmental hygiene, clean and dirty. Pigs were housed individually throughout the experiment. From 61 to 68 days of age (day 0 to 7), pigs were housed in a post weaning unit and feed restriction was applied to half of the pigs from day 0 to day 29. At 68 days of age (day 7 of the experiment), pigs were transferred in a growing unit where half of FR and half of AL pigs were housed in a dirty environment (poor hygiene) and the other half in a clean environment (good hygiene) until day 42. Growth performance was recorded weekly. Blood and faeces samples were collected to measure indicators of inflammation, nutrient digestibility and microbiota composition. Faecal consistency was monitored daily to detect diarrhoeas. Feed restriction decreased daily weight gain (−35% to −50%, P<0.001), increased the feed conversion ratio (+15%, P<0.001) and CP digestibility (+3%, P<0.05) and reduced the occurrence of diarrhoeas irrespective of hygiene conditions. Poor hygiene conditions decreased growth performance (−20%, P<0.05) and total tract digestibility of all nutrients (P<0.001). Haptoglobin (+50%) concentrations and lymphocyte (+10%) and granulocyte (+40%) numbers were higher in poor hygiene conditions (P<0.05), confirming that the model was effective to induce a systemic inflammatory response. Both feed restriction and hygiene modified the profile of the faecal microbiota. In this study, feed restriction did not reduce the systemic inflammatory response caused by poor hygiene conditions despite the limitation of the occurrence of digestive disorders. However, our study opens discussions regarding the impact of hygiene and feed restriction on gut microbial communities and digestive health.

A lack of knowledge about rabbit herbage intake during grazing limits the development of organic rabbit production. This study describes rabbit herbage intake under a wide range of grazing conditions and characterises the factors that decrease rabbit herbage intake and daily weight gain. It was conducted with growing rabbits reared in moving cages with 0.4 m2 of grazing area per rabbit. Rabbits grazed on pastures dominated by legumes (LEG) or grass and forbs (GRF) and received 60 g/day per rabbit of a complete pelleted feed. Three trials were performed in winter, summer and spring. Mean herbage allowance was 27% higher in LEG (62.3 g dry matter (DM)/kg metabolic weight (MW), equal to kg0.75) than in GRF (49.2 g DM/kg MW). Herbage intake varied greatly (36.3±18.0 g DM/kg MW) among trials and was higher in LEG than in GRF (39.5v.34.1 g DM/kg MW). For both pasture types, herbage intake was logarithmically related to herbage allowance and plateaued around 75 g DM/kg MW. Crude protein and digestible energy (DE) intake differed by pasture type and season. Mean CP intake was 40% higher in LEG (15.0 g/kg MW) than in GRF (10.7 g/kg MW). In summer, mean DE intake was 27% higher in LEG than in GRF but no significant differences in DE intake were found between LEG and GRF in winter and spring. Maximum DE intake plateaued near 1000 kJ/kg MW. Daily weight gain was always higher for rabbits grazing LEG (mean=22.6 g) than GRF (mean=16.0 g). Weight gain was significantly related to CP intake, whereas DE intake had no significant effect. Meeting the objective of mean daily weight gain of 20 g requires herbage intake of 32 and 50 g DM/kg MW in LEG and GRF, respectively. Therefore, according to the herbage use efficiency observed in our experiments, herbage allowance must reach 42 and 78 g DM/kg MW in LEG and GRF, respectively. When herbage allowance is lower, rabbits cannot meet the CP intake (13 g/kg MW) required for this weight gain objective.

Limiting the post-weaning intake of the young rabbit is known to improve its resistance to digestive disorders, whereas a degradation of its housing hygiene is assumed to have a negative impact on its health. This study aims at providing insights into the mechanism of digestive health preservation regarding both host (growth and immune response) and its symbiotic digestive microbiota. A 2×2 factorial design from weaning (day 28) to day 64 was set up: ad libitum intake or restricted intake at 70% of ad libitum, and high v. low hygiene of housing (n=105 per group). At day 36 and day 45, 15 animals/group were subcutaneously immunized with ovalbumin (OVA) to assess their specific immune response. Blood was sampled at 36, 45, 57 and 64 days of age to determine total and anti-OVA immunoglobulin type G (IgG) and haptoglobin levels. The cecal bacterial community was explored (18 per group) by 454 pyrosequencing of genes coding for the 16S ribosomal RNA, whereas cecal pH, NH3 and volatile fatty acid (VFA) concentrations were measured to characterize fermentative activity. A 30% reduction in feed intake reduced the growth by only 17% (P<0.001), and improved the feed conversion ratio by 15% (P<0.001), whereas the degradation of hygiene conditions slightly decreased the feed intake in ad libitum fed rabbits (−3.5%, P<0.02). As poor hygiene conditions did not affect weight gain, feed conversion was improved from day 42 (P<0.05). Restricted feeding led to a lower mortality between day 28 and day 40 (P=0.047), whereas degraded hygiene conditions decreased overall morbidity (7.8% v. 16.6%; P<0.01). Both a reduced intake and low hygiene conditions of housing affected microbiota composition and especially dominant genera belonging to the Ruminococcaceae family (P<0.01). Moreover, low hygiene was associated with a higher Ruminococcaceae/Lachnospiraceae ratio (3.7 v. 2.4; P<0.05). Cecal total VFA and pH were increased (+19%; P<0.001) and decreased (−0.1 pH unit; P<0.05), respectively, in feed-restricted rabbits. Neither specific anti-OVA IgG nor haptoglobin was affected by treatments. Total IgG concentrations were the highest in animals raised in poor hygiene conditions after 8 days of restriction, but decreased after 19 days of restriction in high hygiene conditions (−2.15%; P<0.05). In conclusion, the degradation of hygiene conditions failed to induce a systematic specific and inflammatory response in rabbit, but reduced morbidity instead. Our results suggest that the microbiota composition would be a helpful source of biomarkers of digestive health.

To get insights into selection criteria for feed efficiency, 2 rabbit lines have been created: the ConsoResidual line was selected for residual feed intake (RFI) with ad libitum feeding and the ADGrestrict line was selected for ADG under restricted feeding (-20% of voluntary intake). The first objective of this study was to evaluate, after 9 generations of selection, the direct and correlated responses to selection on production traits in the 2 lines for traits recorded during growth. Second, applying the 2 feeding conditions used for selection to both selected lines plus the control unselected line (generation 0, G0) in a 2 × 3 factorial trial, the line performances were compared and the gut microbiota of the lines was characterized. The correlated responses in feed conversion ratio (FCR) were remarkably equivalent in both selected lines (-2.74 genetic σ) but correlated responses in other traits were notably different. In the ConsoResidual line, selection for decreased RFI resulted in a small negative correlated response in BW at 63 d old (BW63) and in a null response in ADG. In the ADGrestrict line, on the contrary, the correlated response in BW63 was substantial (+1.59 σ). The 2 selected lines had a FCR reduced by 0.2 point compared with the G0 line, and the same difference was found in both feeding regimens ( < 0.001). Indeed, selection on ADG would lead to heavier animals with no significant reduction of feed costs, whereas selection on RFI leads to lower feed costs and no increase of animal BW under ad libitum feeding. Altogether, our results do not suggest any genotype × environment interaction in the response to feeding regimens. The intestinal microbial communities from efficient rabbits differed from their unselected counterparts in terms of fermentation end products and microbial phylotypes, suggesting a central role of these microbes in the better feed efficiency of the rabbits.

The effects of a quantitative feed restriction on the digestive physiology of the young rabbit remain largely unclear. Several digestive functions were thus analysed in the rabbit after weaning, using a monofactorial design that produces a linear reduction of the intake, from ad libitum (AL group) to 80%, 70% and 60% of AL (I80, I70 and I60). The restriction programme was applied by giving a daily meal during 21 days after weaning (34 days), and then a 4-day transition period was managed where the feed intake was fixed at 80% of the AL group, before to be fed ad libitum till 69 days of age. The young rabbit quickly adapted to the restriction programme, since within 4 days after weaning they ate totally their ration within 6–7 h after the feed distribution at 8:00, while AL animals consumed 75% of their feed between 15:00 and 8:00. From 55 to 59 days old, rabbits of I70 and I60 groups reached the intake of the I80 group within 1 day, and then the feed intake of restricted animals increased progressively without over-eating. From 54 to 69 days old, the intake of the four groups did not differ and averaged 143.7 g/day per rabbit. During restriction, the live weight and the weight gain decreased linearly with the restriction level. From 55 to 69 days, the weight gain increased linearly according to the restriction level previously applied, but the final weight of restricted rabbits remained lower than AL ones (−3%, −5% and −7%, respectively, for I80, I70 and I60). After 7 days of restriction, the digestibility was not significantly affected by the restriction level, except for crude protein that presented a slightly higher (+1.5 unit, P = 0.05) coefficient in I70 and I60 groups. The mean retention time (MRT) of particles increased by 50% for restricted animals (mean: 26.2 h for I80 and I60) compared to the AL ones, while that of the liquid phase (three times longer than the particles) was linearly and moderately increased with restriction (+20% between AL and I60). In restricted groups, the caecal pH was lower (−0.3 unit, P < 0.05) and could be related to their higher volatile fatty acid (VFA) concentration (+16 mmol/l compared to AL, P < 0.05). The fermentation pattern, ammonia concentration and the caecal bacterial fibrolytic activity remained similar among treatments, although the butyrate proportion tended to be higher in restricted animals. Impact of feed restriction on performances and digestive health is reported in the second part of this study.

Given the very recent investment in research on organic rabbit production, many knowledge gaps remain. Simulation models based on data from experiments and farms may help generate general principles for organic rabbit production. Our goals were to (i) develop a model to simulate intake regulation and growth of rabbits raised on pastures, (ii) validate this model under a diversity of conditions and (iii) conduct a simulation experiment to predict the potential to decrease the supply of complete feed by increasing the grazing area per rabbit. The model developed (PASTRAB) simulates organic rabbit fattening on pastures in four main submodels that represent dynamics of (i) herbage standing biomass, fill and feed values; (ii) intake of herbage, complementary feed (i.e. complete pellets, cereal–legume grain mixtures) and hay as regulated by herbage allowance, fill and feed values of feedstuffs and rabbit physiological parameters; (iii) conversion of rabbit intake into live weight gain; and (iv) rabbit mortality. The model also calculates gross margin per rabbit sold. Model accuracy was assessed by considering the fit between observed and predicted herbage intake, which was low, with a relative root mean square error (rRMSE) of 51% and 66% on grass-based and legume-based pastures, respectively. However, the standard deviations of observed herbage intake were similar to the root mean square error of predicted herbage intake, indicating that it would have been difficult to improve model calibration. The fit between observed and predicted rabbit live weight was acceptable, with an rRMSE of 11% and 10% for grass-based and legume-based pastures, respectively. Simulated scenarios showed that a decrease in complementary feed combined with an increase in the grazing area per rabbit had little impact on average daily growth and gross margin per rabbit but increased herbage use efficiency. With 90 g of complementary feed per day and grazing of 0.4 m²/rabbit per day, herbage use efficiency was 22%, with average daily growth of 21.6 g/day and gross margin of 18.80 €/rabbit. With no complementary feed and grazing of 1.2 m²/rabbit per day, average daily growth decreased (19.2 g/day), but herbage use efficiency reached 100% and gross margin reached 19.20 €/rabbit. We used PASTRAB in participatory workshops with farmers so that the latter could explore adaptations to their current practices. Overall, farmers considered the model predictions realistic, and some of them decided to adapt some of their management practices immediately after the workshops.