Sampling of digestive contents by ileal cannulation in the rabbit

Effect of type of diet (casein-based or protein-free) and caecotrophy on ileal endogenous nitrogen and amino acid flow in rabbits

Twenty-eight New Zealand White X Californian doe rabbits weighing 3791±141 g were surgically fitted with a glass T-cannula at ileum level. Animals were given ad libitum access to either a casein-based diet (C) or a protein-free diet (PF). The only difference in the ingredient composition of the diets was the substitution of 160g/kg of maize starch by casein in the C diet. Animals were randomly allotted to each experimental diet. Seven rabbits per diet were not allowed to practice caecotrophy. The C diet resulted in higher food dry matter (DM) intake (DMI) (111-5 v. 51-5 g/day), food nitrogen intake (3-12 v. 0-20 g/day), ileal flow of DM (56-0 v. 23-8 g/day) and ileal flow of nitrogen (0-72 v. 0-24 g/day) but lower soft faeces DMI (21-7 v. 41-4 g/day) than the PF diet. A linear relationship between ileal endogenous nitrogen flow and total DMI was found for animals given the C but not for the PF diet. The ingestion ofC diet led to a higher (proportionately 0-41, on average), endogenous ileal amino acid flow than PF diet for all amino acids except for glycine. The ileal flow of glycine was proportionately 0-25 higher in animals given the PF diet than in animals given the C diet. The C diet resulted in higher content of nitrogen, threonine and proline in soft faeces than the PF diet. In contrast, the ingestion of the PF diet led to a higher content of lysine and methionine in soft faeces than the C diet. Within the C diet, animals practising caecotrophy showed higher ileal flow of DM (73-4 v. 56-0 g/day) and phenylalanine (0-834 v. 0-677 g/kg DMI) than animals not practising it. Caecotrophy led to a higher endogenous proportion of some of the most important limiting essential amino acids in rabbits, such as arginine, lysine, phenylalanine and threonine. In rabbits, the use of PF diets has limited practical application in the estimation of nitrogen endogenous losses as the low food DMI and the high soft faecesDMI leads to abnormal food: soft faeces intake ratio. Moreover, due to the important effect of caecotrophy on the amino acid composition of endogenous losses, it is important to correct the total amino acid content of the ileal chyme by the undigested amino acid residue coming from the soft faeces intake. This correction could be made, without the methodological complexity implied, by fitting animals with a wooden collar and thereby avoiding caecotrophy as in the present trial.

Effect of fibre source on ileal apparent digestibility of non-starch polysaccharides in rabbits

Sixteen New Zealand White ✕ Californian doe rabbits (four per diet) weighing 3397 (s.e. 378) g, and surgically fitted with a glass T-cannula at the terminal ileum were used to determine the apparent ileal digestibility of non-starch polysaccharides of four fibrous foods. Four diets were formulated to contain paprika meal, olive leaves, lucerne hay or soya-bean hulls as the sole source of fibre. Fibre sources were supplemented with different proportions of soya protein isolate, wheat flour, lard, sodium chloride, calcium carbonate, calcium phosphate, DL-methionine and a mineral/vitamin mix, to obtain diets containing at least 185 g crude protein and 50 g starch per kg. All diets included 2 g/kg of the respective fibre source marked with chromium. Diets were assigned to individually caged rabbits in a completely randomized design and were offered ad libitum throughout the experiment. Dry matter intake was not affected by type of diet. Fibre source affected (P< 0·05) corrected ileal apparent digestibility of total non-strach polysaccharides (NSP), xylose, galactose, glucose and uronic acids. Uronic acids were the best digested monomer at the ileum in all the foodstuffs studied, ranging from 0·195 to 0·522 for olive leaves and paprika meal, respectively. Corrected ileal apparent digestibility of uronic acids was correlated with the uronic acids insoluble in NDF solution, expressed as proportion of total uronic acid content (r=–0·74;P= 0·001), the proportion of large particles (> 1·25 mm;r= –0·71;P< 0·01) and the proportion of fine particles (< 0·315 mm;r= 0·65;P= 0·01). Other monomers (arabinose, mannose, rhamnose and galactose) usually related to pectic substances, also showed in general a greater ileal digestibility than that of total NSP. Taking into account the uronic acids content of the diet and their digestibility, digestible uronic acids accounted for 0·572, 0·528, 0·93 and 0·353 of the total ileal digestible NSP of paprika meal, olive leaves, lucerne hay and soya-bean hulls based diets, respectively. The sum of arabinose, mannose, rhamnose and galactose accounted for 0·15 of total NSP digested at the ileum on average, over the different fibre sources studied. Glucose and xylose were the monomers least digested at the ileum. Their corrected ileal apparent digestibilities were close to zero, except for the paprika meal (0·266 and 0·216) and soya-bean hulls (0·137 and 0·057) based diets. In conclusion, the results of this study indicate that a valuable amount of total NSP is hydrolysed before the caecum in rabbits. However, this hydrolysis affects mainly pectic and readily fermentable substances.

[The effect of very low and moderate fiber levels on metabolism in the cecum of growing rabbits]

Investigations with 15N'-labelled urea were carried out to find out the influence of the amount of fibre on the reflux of 15N' into the caecum to take part in the caecal metabolism. Two pelleted diets, containing 9.7% (group 1 with 23% oat hulls) and 2.2% (Group 2 without oat hulls) crude fibre, with urea with 60 atom% 15N-excess (15N) used as marker were given to three White New Zealand rabbits each group. Group 1 and 2 consumed 109 and 72 g fresh matter per rabbit and day, respectively. Daily 15N'-intake per rabbit was 307 mg in group 1 and 279 mg in group 2. Most of 15N' was eliminated directly via the urine. The daily faecal excretion in group 1 and 2 was 5.3 and 2.3 mg 15N', respectively. Only about 20 to 30% of 15N' and volatile fatty acids in the caecum and higher amounts of 15N' in muscles were found. The animals of this group consumed nearly the total amount of faeces by caecotrophy. Therefore 24 g of group 2 was still satisfying compared to 33 g live weight gain/rabbit and day of group 1. It is concluded that the animals of group 2 could compensate the low fibre level within a period of about 20 days by a more efficient utilization, the consumption of crude protein and starch being 18 and 12% lower than in group 1, respectively. Feed intake and health status were not evidently affected. The results are in contradiction to the common knowledge.

Effect of fibre level, particle size and adaptation period on digestibility and rate of passage as measured at the ileum and in the faeces in the adult rabbit

The use of specific methods other than gravimetric ones to analyse fibre permitted a more precise study of the degradation of cell wall (CW) in the digestive tract. Digesta flow and rate of passage measurements have not been assessed previously in rabbits to investigate fibre digestion and fibre effects simultaneously in the proximal and in the distal segments of the tract. The effect of the level of dietary fibre on ileal and overall digestibility and rate of passage were studied by comparing semi-purified diets containing only one source of CW (dehydrated lucerne (Medicago sativa) meal) given to adult female rabbits. The effect of fibre particle size and adaptation period were also investigated. Measurements of fibre composition using both colorimetric and gas-liquid chromatographic techniques, showed that large amounts of (CW) were degraded in the caecocolic segments. Increasing dietary fibre level reduced the rate of passage but fibre degradation was increased, at the same time a lower digestive efficiency for energy in the small intestine was found. A small quantity of CW was apparently degraded before the caecum, assuming that the water-soluble fraction of CW was essentially implicated. Grinding lucerne meal through a 1 mm instead of a 3 mm screen did not improve CW digestibility in spite of a longer rate of passage in the caeco-colic segments. Adaptation to a high-fibre diet resulted in an higher digestive volume for colon and caecum, related to an improved degradation of CW. Furthermore, digestive efficiency in the small intestine appeared higher for rabbits adapted to a high-fibre diet than that for rabbits initially fed on a low-fibre diet.