Effects of Levels of Insoluble and Soluble Fibre in Diets for Growing Rabbits on Faecal Digestibility, Nitrogen Recycling and in Vitro Fermentation

Abstract

AbstrAct:The effect of neutral detergent fibre (NDF) and neutral detergent soluble fibre (NDSF) on in vivo faecal digestibility and caecal fermentation pattern was studied in growing rabbits, in 4 diets formulated according to 2 levels of NDF, 370 (LI) and 450 (HI) g/kg, and 2 levels of NDSF, 150 (LS) and 180 (HS) g/ kg in substitution of starch, in a 2×2 factorial structure. Twenty four New Zealand White rabbits weaned at 28 d (630±80.2 g weight) were allocated to digestibility cages from 42 to 49 d of age to determine apparent faecal digestibility of each diet (n=6). Urine was collected for determination of purine derivatives (PD). Once the digestibility trial finished, rabbits were fitted with PVC neck collars for 24 h total caecotrophe collection. After 1 d of recovery, animals were slaughtered and caecal contents were used as inocula for 18 h in vitro gas production and caecal degradation (ivDMcD) study, using an HCl-pepsin and pancreatin pre-digested substrate. Diet digestibility was also determined by the in vitro three-step enzymatic procedure. There were no effects of the NDF×NDSF interaction for any digestibility parameter (P>0.10). Both dry matter and organic matter digestibility (DMd and OMd) decreased from 0.518 to 0.442 and from 0.526 to 0.447, respectively, with the increase of NDF (P<0.001), but were unaffected by the NDSF level (P>0.10). In contrast, NDF digestibility (NDFd) and ivDMcD did not respond to NDF (P>0.10) but increased from 0.156 to 0.200 and 0.141 to 0.210 with the proportion of NDSF (P<0.01). Weight of caecal contents increased with both NDF (P<0.001) and NDSF content (P<0.01). However, total production of caecotrophes increased from 20.1 to 25.5 g DM/d with NDF (P<0.05), but was not affected by NDSF. The crude protein (CP) proportion in caecotrophes decreased with NDF (P<0.001) and increased with NDSF level (P<0.01), and total CP recycled as caecotrophes tended (P=0.093) to be higher in HS diets, being unaffected by the dietary level of NDF. Diets rich in NDSF rendered higher gas volumes (P<0.001) than those with LS from 2 to 18 h incubation, whereas inclusion of high proportions of NDF reduced gas volume (P<0.01). Results indicate that NDF reduces faecal digestibility, whereas NDSF promotes better conditions for caecal fermentation.

Influence of inoculum type (ileal, caecal and faecal) on the in vitro fermentation of different sources of carbohydrates in rabbits

“…Both SBP and wheat straw were subjected to a predigestion procedure to simulate the digestion in the stomach and small intestine, as described by Abad et al (2013) and using ANKOM filter bags (F57; 25 µm pore size; Ankom Technology, New York, USA). Briefly, samples were first incubated in a pepsin solution (2000 FIP-Units/g protein, Merck n7190, Merck, Darmstadt, Germany; 25 mg pepsin/mL 0.2 M HCl; pH=2.0) at 40°C for 1.5 h, and then in a pancreatin solution (Grade VI, Sigma 1750, Sigma-Aldrich Quimica, (Bindelle et al, 2007;Rodríguez-Romero et al, 2011;Abad et al, 2013).…”

Impact of rearing mangement on health in domestic rabbits: a review

“…This can be accomplished either using feed with low nutrient density or feed with a high structural carbohydrate content (Rodríguez- Romero et al, 2011;Martínez-Vallespín et al, 2011, by limiting the intake of pelleted all-mash feed until postnatal week 8 (Schlolaut et al, 1978;Schlolaut and Lange, 1979;Gidenne et al, 2003Gidenne et al, , 2009), or by actively restricting the feeding time (Schlolaut and Lange, 1990;Romero et al, 2010). If despite the premature developmental state of the digestive system high growth rates are to be achieved by feeding pelleted all-mash feed ad libitum starting at postnatal day 17, or if the young have access to the mother's food, it is necessary to reduce the proliferation of pathogens by adding bacteriostatic or bactericidal food supplements.…”

In vitro caecal fermentation of carbohydrate-rich feedstuffs in rabbits as affected by substrate pre-digestion and donors' diet

“…Samples (250 mg DM) of each substrate were carefully weighed into 115-mL glass vials. In half of the vials, the substrates were subjected to a 2-step pepsin-pancreatin in vitro digestion (pre-digestion) according to Ramos et al (1992), with the exception that the contents of the vials were not filtrated at the end of the procedure. All vials were stored at 4°C overnight (to stop the digestion) and placed in an incubator at 40°C for 1 h before starting the in vitro incubations.…”

“…However, the use of this procedure with substrates with low or even no content of starch and protein could limit this effect. In addition, donors' diet has been shown to influence the in vitro gas production and substrate degradability in pigs and ruminants (Bindelle et al, 2007a,b;Mateos et al, 2013;Sappok et al, 2013), but information on the effects of donors' diet on in vitro caecal fermentation in rabbits is very limited (Rodríguez-Romero et al, 2011). The aim of this study was to assess the in vitro caecal fermentation of four carbohydrate-rich substrates as influenced by the pre-digestion process and donors' diet.…”

“…The use of in vitro methodologies to study the microbial fermentation of carbohydrate-rich substrates in rabbits may be of interest, but a standardised in vitro methodology is not yet available. Some studies have used the in vitro gas production technique (Menke et al, 1979) to investigate caecal fermentation in rabbits, and in most of them (Bovera et al, 2006(Bovera et al, , 2009Lavrenčič, 2007;Calabrò et al, 2010;Yang et al, 2010) substrates were just ground, but in others (Bindelle et al, 2007a;Bindelle et al, 2007b;Rodríguez-Romero et al, 2011) the insoluble residue obtained after the pepsin-pancreatin in vitro predigestion was used as substrate. Whereas this latter procedure might seem more appropriate (Coles et al, 2005), it is also questionable due to the loss of soluble fibre during the filtration/centrifugation process.…”