Search

This work aimed to study the stability over time of the bacterial community in caecum and faeces of the rabbit (diversity index and structure) without experimental disturbance and to evaluate its relationships with environmental parameters. Soft and hard faeces of 14 rabbits were sampled for 5 weeks while caecal content was sampled on the 3rd week (by surgery) and the 5th week (at slaughter). Bacterial communities were assessed by studying CE-SSCP profiles of 16S rRNA genes fragments. Redox potential, pH, NH3-N concentration and volatile fatty acid concentrations were measured in the caecum. Data showed that bacterial communities of soft and hard faeces barely differed from that of the caecum (ANOSIM-R<0.25; p<0.05). Without disturbance, the bacterial communities of faeces were stable over time (ANOSIM-R<0.25; p<0.001). However, the bacterial communities of caecum and faeces were affected by the surgery (ANOSIM-R=0.22-0.33; p<0.001). The caecal content was an acidic (pH=6.03+/-0.33) and an anaerobic environment (redox potential=-160+/-43 mV). Only the redox potential was correlated with the diversity index of the bacterial community of the caecum (R(2)=0.35; p<0.05) and no environmental parameters were correlated to its structure., (Copyright 2009 Elsevier Ltd. All rights reserved.)

Carcass traits and meat quality of rabbits reared in conventional cages (0.385 m2), small pens (0.662 m2) or large pens (4.052 m2) at a similar stock density of 15 rabbits/m2 were compared (n = 30 per group). Pens contained an elevated platform. Slaughter weight (SW; P < 0.01) and cold carcass weight (P < 0.05) decreased in the order of Cage < Small pen < Large pen groups. SW and cold carcass weight were 7% lower in rabbits housed in large pens than in cages. Dressing out and meat-to-bone ratio were not influenced by the housing system. Percentage of fat deposits was highest in caged rabbits (+0.15 point for scapular fat and +0.26 point for perirenal fat compared to rabbits reared in large pens P < 0.05). Rabbits housed in large pens had a bigger proportion of hind part (+1 point), and meat colour was shifted towards greater a* values (P < 0.01) compared to caged rabbits. Water holding capacity and shear test parameters in longissimus lumborum muscle, lipid content and shear test parameters of abductor cruralis cranialis, biceps femoris and semitendinosus muscles were not affected by the housing system. Tibia and femur bone moment of inertia increased in the order of Cage < Small pen < Large pen groups (P < 0.05), whereas elastic modulus, which is a measure of intrinsic stiffness, was highest in caged rabbits. This study showed that large pen housing altered carcass traits independently and increased meat redness and fracture resistance of tibia and femur.

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.

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 (-4.5 g/% of restriction), but relatively moderate: the weight loss of the more-restricted rabbits (60%) reached 7.7% (-200 g) compared to the AL group. Over the whole fattening period, the feed restriction reduced linearly and significantly the feed conversion (FC) (-0.0077 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: -9% compared to AL). The morbidity was also significantly reduced (-6%) 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.

A bacteria library was constructed from the caecum of a rabbit maintained under standard conditions. The complete gene 16S rRNA gene was sequenced. The 228 clones obtained were distributed in 70 operational taxonomic units (OTUs). The large majority of the OTUs were composed of one or two clones and seven OTUs contained half of the sequences. Fourteen sequences had high similarity to the sequence already registered in databases (threshold of 97%). Only one of these sequences has been identified as Variovorax sp. (99% identity). Units were distributed mainly (94%) in the Firmicutes phylum. Three sequences were related to Bacteroidetes. Nine clusters were defined in the phylogenic tree. A great diversity of caecal bacteria of the rabbit was shown. Half of the sequences generated in this library were distributed in the phylogenetic tree near the sequences characterized previously in rabbit caecum (potential core species), and the other half of the sequences were well separated (satellite species).

Enteropathogenic Escherichia coli (EPEC) represents a major cause of lethal diarrhea in young mammals. Although the pathogenicity mechanisms of EPEC are now well understood, the intrinsic and environmental factors that control the expression of EPEC virulence remain largely unknown. In the rabbit, suckling reduces pups' sensitivity to EPEC infection. Hence, we have hypothesized that uncharacterized factors present in doe milk may mediate this protection. Medium chain fatty acids (MCFA), known to possess antimicrobial properties, are highly abundant in doe milk. We demonstrate that caprylic acid exhibits a clear bacteriostatic effect in vitro against the rabbit EPEC strain E22 (O103:H2:K-), in a dose-dependent manner. In vivo, the dietary inclusion of triglycerides of MCFA did not however reduce the sensitivity of young rabbits challenged with this EPEC strain. The mortality and fecal excretion of EPEC were not reduced, and the bacterial adhesion to ileum was not inhibited. Amount of MCFA reaching the ileal level might have been too low and/or their association to other milk antimicrobials may have been required to observe a positive effect on disease evolution in a context of a highly virulent challenge.

The ability of young rabbits to digest a solid diet was evaluated according to the weaning age: 21 (W21, 12 litters) or 35 (W35, 12 litters) days of age. From 14 days onwards, the rabbits were fed the same pelleted feed. Three methods were compared to estimate the faecal digestibility in the young rabbits, between 24 to 28 and 38 to 42 days. Digestive balance at ileal and faecal levels was determined for the main nutrients provided by milk and solid feed. The W21 rabbits increased their solid feed intake only 2 days after their weaning, when compared with suckling rabbits. Thus, their crude protein (CP) intake remained lower until 26 days compared with the W35 rabbits (from 41%, P < 0.01), as well as their crude fat intake until 28 days (from 72%, P < 0.001). On the contrary, the W35 rabbits increased their solid feed intake without a delay after weaning, quickly reaching the intake level of the W21 rabbits. The amounts of organic matter (OM) and CP reaching the caecum were increased on day 28 by 56% and 42% in the W21 rabbits compared with the W35 rabbits, respectively (P < 0.05), and were similar between groups on day 42. Starch ileal digestibility coefficients were 94·2% and 95·4% in 28- and 42-day-old rabbits, respectively, irrespective of the weaning age. The amount of starch flowing through the ileo-caecal junction was low and only tended to be higher on day 28 in the W21 group (0.20 v. 0.15 g/day in the W35 group, P = 0.10). The digestive balance pointed out that the digestible energy intake was similar between weaned and suckling rabbits from 23 to 27 days, a phenomenon partly explained by a high ability of the W21 rabbits to digest starch (98%) and NDF (36%). Indeed, the amounts of starch and NDF digested by the W21 group were 2.0- and 2.4-fold higher than those of the W35 rabbits at this period (P < 0.001). However, they ate 20% less digestible proteins than still-suckling rabbits (P < 0.001). From 38 till 42 days, only a lower ability of the W21 rabbits to digest lipids was detected (P < 0.05). In conclusion, early-weaned rabbits were able to adapt quickly to digest large amounts of starch and fibres.

The functional adaptability of the digestive system to the level of feed intake was investigated in the young rabbits by comparing two groups of 12 litters each, weaned at 21 (W21) or 35 (W35) days of age. From 14 days onwards, rabbits were fed a pelleted feed (NDF: 332 g/kg, CP: 177 g/kg, starch: 98 g/kg, as-fed basis). Until 49 days of age, the profile of digestive enzymes was weekly determined in the small intestinal content and mucosa, as well as caecal fermentation traits and fibrolytic activities. In the W21 group, the solid feed intake was increased by 57% between 21 and 35 days (P < 0.01), while the daily body growth was lower from 21 till 42 days (-17%, P < 0.05) when compared with the W35 group. Activities of enzymes of pancreatic origin were only scarcely influenced by the weaning age. In the W21 group, amylase activity tended to be lower at 28 days of age (-36%, P = 0.064), and trypsin activity was decreased by 31% at 49 days of age (P < 0.01). Lipase activity was similar in both weaning groups. Duodenal and jejunal activities of maltase and aminopeptidase N (APN) were higher on day 28 in the W21 group as compared with the W35 group (×1.4 to ×2.4, respectively, P < 0.05). On day 35, duodenal APN activity was twice as higher in the W21 group than in the W35 group (P < 0.01). In caecum, major differences between both weaning groups were observed at 28 days of age with a decrease in ammonia concentration (-43%, P < 0.01) in W21 compared with W35 rabbits. Conversely, the acetate proportion was 5% higher in the W21 group (P < 0.01) on day 28. In conclusion, the digestive tract of early-weaned rabbits showed some adaptative properties in response to nutritional environment changes, but they were insufficient to maintain their growth rate.

The developmental changes of intestinal digestive potential and caecal microbial activity were described in suckling and weaned rabbits according to two feeding programmes. Two groups of thirteen litters were fed from 18 to 42 days old a "High" or a "Medium" NDF:starch ratio diet (resp. 2.7 vs 2.0, groups HL and ML) with similar protein and lipid levels, and from 42 to 70 days old the two groups were fed a "Low" NDF:starch ratio diet (1.7). From 25 to 32 days (weaning), the milk and solid feed intake were 22% and 41% higher in ML group (P<0.05), and the mortality by diarrhoea was 4 units lower (P<0.01). The whole tract digestive efficiency increased by 10% before weaning, and remained steady (organic matter) or decreased (lipids, protein) after weaning. Energy digestibility was 0.623 and 0.686 for High and Medium diets respectively. From 25 to 42 days, total enzymatic activity in intestinal content increased for chymotrypsin (5-fold, P<0.001), lipase (10-fold, P<0.001), amylase (17-fold, P<0.01) and maltase (11-fold, P<0.001), while trypsin doubled after weaning. The feeding programme only affected the amylase and maltase activities, that were higher in HL group (P<0.05). The volatile fatty acids concentration in the caecum was not significantly different among the groups, but it increased by 44% 10 days after weaning. The bacterial fibrolytic enzymes, increased by 30% after weaning and were similar among the two groups. The study revealed that the intestinal digestive maturation and the caecal microbial activity of the rabbit evolved markedly between 3 and 5 weeks of age, and was weakly affected when the NDF:starch ratio decreased from 2.7 to 2.0.

Enteropathogenic Escherichia coli (EPEC) colibacillosis represents a major cause of lethal diarrhea in young children in developing countries. EPEC strains also infect numerous mammal species and represent a major economical problem in rabbit industry. Protection against this pathogen is a challenging goal both in humans and in other mammal species. Despite a good knowledge of the pathogenicity mechanisms of EPEC, the intrinsic and environmental factors that control the expression of EPEC virulence in mammals remain unknown. For instance, the exacerbated sensitivity of young mammals to EPEC infection is still unexplained. Our goal was to investigate if age or other factors, like milk consumption, could be determinants that trigger the disease. We used rabbits as an animal model to study the role of milk in the sensitivity to an EPEC infection. Weaned and suckling rabbits were orally inoculated with EPEC strain E22 (O103:H2:K-) at 28 days of age, and the evolution of the disease was investigated in the two groups. In addition, in order to better characterize the interactions between milk and EPEC, we determined in vitro bacterial growth and the abilities of EPEC cells to adhere to epithelial cells in the presence of milk. Our results demonstrate a protective role of milk in vivo in association with in vitro antibacterial activity. These effects are independent of the presence of specific anti-EPEC antibodies.

The impact of dietary factors on the gut morphological maturation is poorly documented in rabbits. The weights of the digestive segments as well as the morphology of villi and crypts along the small intestine were analysed weekly from day 14 till day 49, in two rabbit groups weaned at either 21 (W21 group, n = 12 litters) or 35 days (W35 group, n = 12 litters) of age. From 21 till 35 days, the W21 group ate 57% more solid feed than the W35 group (P < 0.01), and presented slighter body weights from day 28 till day 49 (-9%, P < 0.05). Tissue weights of the empty digestive segments, as expressed relative to the body weights, were higher in the W21 than in the W35 group from day 28 till day 49 (P < 0.001), whereas absolute tissue weights appeared similar (except for the proximal colon). From day 28 to day 49, small intestinal villi grew in height and surface area (P < 0.05) whereas the crypts deepened. Villous height followed a proximo-distal decreasing gradient from the duodenum to the ileum (P < 0.05) from day 28 onward. The villous height to width ratio changed with the beginning of significant solid feed intake: from a thin shape until day 21, villi became wider from day 28 on. The effect of weaning age on mucosal morphology was insignificant, except for the jejunal crypts whose surface area and depth were higher in the W21 group. The present results showed that morphological changes in the digestive tract of young rabbits were weakly influenced by an early stimulation of solid feed intake.

The postweaning development of caecal microbial activity was studied in the rabbit according to the sanitary status (conventional "C" vs. specified pathogen-free "SPF") and the nutritional status (standard-fibre "SF" vs. deficient-fibre "DF" diet). The two diets were distributed ad libitum from weaning (28 days) to 70 days of age, respectively, to 80 C and 72 SPF rabbits. From 28 to 42 days, the volatile fatty acids concentration in the caecum (tVFA) of C rabbits was 50 mM/L and increased by 46% between 42 and 56 days, without interactions with the diet effect. In parallel, the bacterial fibrolytic activity decreased for xylanase and CMCase (-32% and -60%, respectively, P<0.05), while pectinase activity decreased more regularly from 28 to 70 days (-28%, P<0.05). At weaning, tVFA was similar among C or SPF rabbits, while at 70 days, it decreased by 23% for SPF and increased in C group (+31%). Cellulasic and hemicellulasic activity of bacteria were two to three times lower, respectively, in SPF rabbits compared to conventional ones. No interaction was detected between sanitary and nutritional status at 70 days of age for the caecal fermentative activity. With the FD diet, tVFA decreased by 10%, while butyrate proportion increased by 37% (at 70 days), whatever the sanitary status. In 70-day-old rabbits (C or SPF group), pectinasic activity was reduced by 30% when rabbits were fed the FD compared to the SF one.

Caecal microbial activity, digestion and gut health were analysed in the young rabbit, in response to fibre substitution by starch, in diets with high proportions of rapidly fermentable polysaccharides (pectins+hemicelluloses:acid-detergent fibre (ADF) ratio of 1.7). A range of five diets corresponding to a 60 % linear reduction of the ADF level (230 to 92 g ADF/kg) without changes in the fibre quality, and to a corresponding linear increase in dietary starch, was given ad libitum to young rabbits from 18 d until 70 d of age. A one half reduction of the ADF level resulted in a sharp increase in energy digestibility (+25 units), associated with a lower feed intake (-35 %) and to an increase of the mean retention time (+6 h) in the whole digestive tract. Despite large variations in the fibre intake (20 to 59 g ADF/d), the fibre digestive efficiency remained similar among the five diets. Starch ileal concentrations were low after 4 weeks of age (<5 %), and variations with age were significant when the dietary starch level was over 19 %. A 65 % lower biomass production was measured when the ADF level progressed from 230 to 165 g/kg, and no precise relationship was found with fermentative activity. Reducing the fibre intake led to a linear decrease of caecal volatile fatty acids concentrations, and to higher pH and NH3 levels. An increased occurrence of mortality by diarrhoea was registered with the lowest fibre intake. It can be concluded that a sufficient supply of fibre, with high proportions in rapidly fermentable polysaccharides, stimulates the maturation of microbial activity and reduces the occurrence of diarrhoea.

The developmental changes of both pancreatic and intestinal enzymes and the influence of dietary composition on enzyme activities were followed in suckling and weaning rabbits. In addition, whole tract digestibility of nutrients was recorded in response to two dietary energetic sources. Rabbits were fed ad libitum either a low fat and high starch diet (group LF), or a high fat and high fibre diet (group HF) between d 32 and d 42, with both groups receiving a growing finishing diet thereafter. Before weaning (d 32) nutrient digestion was high (>75% for organic matter, protein or fat), and then decreased sharply, except for fat. Between d 32 and d 42, digestion in the HF group was 7.5 and 4.6% lower, respectively, for organic matter and protein, while fibre and fat digestion was higher (+14.0 and +5.0%, respectively). Between d 25 and d 42 of age, pancreatic-specific activities of trypsin and chymotrypsin did not change while those of amylase and lipase increased by 1.5- and 76- fold (P<0.05), respectively. However, total activities and relative activities expressed on a LW basis were increased after weaning as a main consequence of a specific increased organ weight and pancreatic protein content. Relative activities of trypsin and chymotrypsin increased by 63 and 56% (P<0.01) after weaning, respectively. Total activities of pancreatic enzymes measured in the total small intestinal contents increased during the same period, but the range of variations was lower than those measured in the pancreatic gland. Total activities of lipase, trypsin and chymotrypsin measured in the small intestine contents were significantly correlated with pancreas enzyme potentialities. Total small intestine activity of lipase was 58% higher (P<0.001) in HF than in LF group while the other pancreatic and intestinal enzyme activities measured were not influenced by the energetic sources of the diet. Decreased digestibility of organic matter and protein observed with the HF diet could not be related to changes in pancreatic or intestinal enzymatic profiles and may be more dependent on quality of dietary ingredients.

The milk/solid feed intake pattern and digestive capacity were compared in two groups of young rabbits reared between 16 and 32 days in litters of four (L4 group, n = 18 litters) or ten pups (L10, n = 20) in order to modulate milk availability. Compared to the L4 group, rabbits in the L10 group presented a lower milk intake (22.3 versus 28.8 g x day(-1)) and a higher solid feed intake (12.9 versus 8.0 g x day(-1)) between 16 and 32 days of age. Live weight and weight gain were significantly lower in the L10 (-15%) than in the L4 group from 22 until 42 days. No significant difference was observed among the two groups for post-weaning digestibility and for the intraluminal specific or total activities of amylase and maltase. The total intraluminal activity (pool of enzyme) of amylase and maltase doubled between weaning (32 days) and 42 days. At weaning, the specific activity of amylase was similar in the jejunal and ileal segments (8.5 AU x g(-1)). From 32 to 42 days, the specific amylase activity doubled in the jejunum, while it remained steady in the ileum. The intraluminal specific maltase activity did not significantly change between 32 and 42 days, while it was twice as high in the jejunum compared to the ileum (3.5 versus 1.8 micromoles hydrolysed maltose x g(-1), respectively).

Thirty-two SPF New Zealand White rabbits of both sexes were used in this experiment. They were sequentially slaughtered at 22, 29, 35 and 42 days of age. The rabbits were only milked by their mother and by foster mothers (no access to solid food) throughout the experiment. They exhibited a caecal fermentation pattern that turned towards a proteolytic metabolic activity (high levels in NH3 and in branched-chain fatty acids and valeric acid: 17 mmol.L-1 and 1 mmol.L-1, on average, respectively). The absence of caecal cellulolytic microflora and the low concentration of the total volatile fatty acids (tVFA) could be explained by the lack of substrate that would have been brought by a solid feed. From day 29 onwards, the low tVFA (12.5 mmol.L-1) and high NH3 concentrations (16.5 mmol.L-1) explained the high pH value (6.8 on average). This could be considered as a pathological value in weaned rabbits, but in our case no clinical signs of diarrhoea were observed. The evolution of the colibacilli flora according to age was similar to that usually described and thus was not correlated with pH, tVFA or cellulolytic flora. The evolution of the colibacilli population (from 10(7) bact/g on day 22 to 10(3) on day 42) seemed dependent on ontogenic factors rather than on the composition of the caecal media (pH, etc.).

The rate of passage (RP) in several digestive compartments was studied in 4 adult female rabbits cannulated at ileum, and receiving ad libitum 3 diets with decreasing fibre content (40, 30 and 22% NDF). The RP values in the whole digestive tract and between ileum and rectum were simultaneously measured by following the fecal kinetics of 2 markers (169Yb and 141Ce adsorbed on the NDF fraction of the diets) given as single doses. The mean retention time (MRT) in the whole tract provided by modelling methods (models: Grovum and Williams or Ellis) were similar to those obtained by reference method (numeric integration). MRT values in the caecum and the stomach were provided by models and were in good agreement with those deduced from reference measurements. Compared with the Ellis model, the Grovum and Williams model estimated more precisely the RP in tubular compartments (ie small intestine and distal colon); but the increasing part of the kinetics was better fitted using the Ellis model, particularly for low-fibre diets. The decrease in fibre intake (-50%) led to a 12 h increase (+72%) of the whole tract MRT, originating mainly from a 2-fold increase of ileo-rectal MRT. The MRT in the stomach decreased from 3 to 1 h, whereas the RP in the small intestine increased. Therefore, the oro-ileal MRT (mean 5 h) was not affected. A low dietary fibre induces a longer cecal MRT of large particles, without significant change for fine particles.

A new technique for caecal cannulation in adult rabbit was validated in order to perform in vivo studies of caecal fermentation under a physiological status. The cannulation did not modify the digestibility of the diet, and it was possible to collect digesta (10 g fresh matter) after a few minutes without stress for animals only 10 days post-surgery. Volatile fatty acid (VFA) (60 mM/l) and ammonia (11 mM/l) concentration of caecal digesta collected in vivo was not different from that obtained from slaughtered rabbits. VFA measurements were reproducible (CV = 6.8%) and were not dependent on the daily collection frequency (1-5/day). Caecal VFA level in the starved rabbit was very low (23 mM/l) while the butyrate/propionate rate was the inverse (C4/C3 = 0.6). Five h after feeding, the in vivo VFA level reached 96 mM/l and the butyrate proportion (12%) over-reached those of propionate (3.5%). The caecal fermentations of a 7-week-old rabbit differed from those of an adult by a higher VFA level and by a greater post-feeding variation in the fermentation pattern.

The influence of adding a fibre rich concentrate feed (wheat bran or beet pulp) to a hay-based diet (orchard grass-lucerne mixture; 50/50) upon the rate of passage of digesta of these two fractions (hay and concentrate) was measured in three groups of 8 adult doe rabbits (White New Zealand x California). The three diets composed of either 90% hay, or hay + bran or hay + pulp were offered at two levels of feeding, i.e. ad libitum and 2/3 ad libitum. The retention time of the two main fractions was measured by means of two tracers, i.e. ytterbium-169 bound to hay and cerium-141 to bran or pulp. Animals fed on the 90% hay diet excreted more than 90% of the tracer during the first 24 h. The mean retention time (MRT) of this diet was the shortest (on an average 14.8 h). The addition of pulp or bran increased the MRT of the diet by 2 and 4 h, respectively. Feed restriction led to a 5 to 7 h earlier period of caecotrophy with a subsequent lengthening of the MRT by 2 to 4 h according to groups. The two hay + "concentrate" diets gave almost the same 169Yb and 141Ce excretion curves. Thus, the mean retention time seems to be the same for digesta from hay and "concentrate" (non significant deviations).

Five adult rabbits (New Zealand White x Californian) were fed ad libitum for 10 days a pelleted feed compound containing dehydrated lucerne whose particles (0.05-0.5 mm in size) were marked with a rare earth, i.e. ytterbium (Yb). In order to estimate the proportion of marker liable to leave its initial site of binding, we measured the amount of ytterbium present on faeces particles larger than 0.5 mm. The total amount of faeces was collected during the following 3 days. The faeces screening technique used in this study was adapted from that applied to feed. However, the repeatability was low for the large particles (greater than 1 mm), whose number was small. Half of the digesta particles (52%) exhibited a smaller size than 0.05 mm. The proportion of large particles (greater than 1 mm) in the faeces was low (1.5%) while that of the other particle classes ranged from 20-33.5%. After pelleting, more than 40% Yb initially bound to lucerne particles measuring 0.5 to 0.05 mm, was present on fine particles (less than 0.05 mm). Accordingly, only minima and maxima amounts of Yb having migrated on large particles (greater than 0.5 mm) could be measured, i.e. 2.5 and 8.9%, respectively of the ingested Yb. Taking also into account a migration towards small particles, about 10% Yb was liable to leave its initial site during its passage through the digestive tract of the rabbit.

The effect of adding a fibre-rich concentrate (wheat bran or beet pulp) to a hay-based diet (cook's foot-lucerne: 50/50) on the apparent digestibility of diets was measured in three groups of 8 adult doe rabbits (New-Zealand White X Californian). Diet composition was as follows: 90% hay only (diet F), hay + bran (diet FS) or hay + pulp (diet FP). Two levels of feeding were tested: ad libitum and 2/3 of ad libitum intake. Addition of wheat bran and especially of beet pulp led to a significant increase in the apparent digestibility of the whole diet. Our results confirm the high digestibility of cell-wall constituents of beet pulp: the apparent digestibility coefficient of hemicellulose in diet FP reached 60% (versus 23% for diet F) and that of cellulose 45% (21% for diet F). Wheat bran supplied digestible hemicellulose (ADC = 48% for diet FS) while the apparent digestibility of bran cellulose was not higher than that of hay (ADC = 22%). This digestive interaction between raw material was accompanied by an interaction with the digestive transit. The less digestible diet (diet F) exhibited the shortest mean residence time (MRT). However, diet FS exhibited the longest residence time whereas it was less digestible than diet FP. These results suggest that, in the rabbit, wheat bran is a transit-regulator as already observed in other species. Measuring apparent digestibility between the 10th and the 16th day of the feed restriction was too early for our doe rabbits. Values measured were not significantly different from those obtained during ad libitum feeding, although the MRT of diets was longer during restricted feeding.

Ytterbium was compared to mordant chromium fiber to estimate ileal flow in adult rabbits. The flows of organic matter (OM) and of cell-walls (CW) were not significantly different between the two markers. CW were not degraded in the intestine, while 49% of digestible OM disappeared before the caecum.

The relative fatty acid profiles of perirenal adipose tissue and muscle tissue of the hind legs were studied in New Zealand rabbits 21 to 140 days old. The rabbits were fed a low-fat diet covering the essential fatty acid requirements and distributed either ad libitum or in rationed amounts. The whole of the fatty acids were established earlier in hind leg muscle tissue than in perirenal adipose tissue. In the latter, the growth allometry of fatty acids in relation to the carcass was already higher between 21 and 74 days (a = 1.39) and distinctly higher between 74 and 140 days (a = 2.68). In the muscle tissue, an isometric phase (a = 0.96) preceded a major allometric phase (a = 1.76). In young suckling rabbits, the fatty acid profile of perirenal lipids was influenced by that of the milk lipids. In the muscle tissue, the presence of a large proportion of phospholipids resulted in a higher percentage of stearic acid and polyunsaturated fatty acids of the (n-6) family (linoleic, dihomo-gamma-linolenic and arachidonic acids). After weaning, the proportion of saturated fatty acids (C greater than or equal to 14) in the perirenal adipose tissue remained constant. The endogenous production of monounsaturated fatty acids (higher allometry) caused a progressive dilution of polyunsaturated fatty acids (lower allometry). This dilution was slowed down when the diet was rationed. Changes in the fatty acid composition of muscle tissue were, in general, comparable to those of perirenal adipose tissue. The differences observed could be attributed to the more active participation of phospholipids in the total lipids of the muscle tissue. Stearic acid, abundant in the phospholipids, showed a lower allometry compared to total fatty acids. Its dilution was an expression of triglyceride dilution of the phospholipids during growth. The same was true of polyunsaturated fatty acids. Rationing had the reverse effect.