Introduction adapted to more concentrated feeds that are efficient-

Livestock Production Science 64 2000 225–237 www.elsevier.com locate livprodsci A comprehensive approach of the rabbit digestion: consequences of a reduction in dietary fibre supply a , a,b c ˜ T. Gidenne , V. Pinheiro , L. Falcao e Cunha a INRA , Station de Recherches Cunicoles, BP 27, 31326 Castanet, France b ˜ UTAD , Secc¸ao de Zootecnia, apt. 201, 5000 Vila Real Codex, Portugal c ˜ ˜ ISA , Secc¸ao de Produc¸ao Animal, Tapada de Ajuda, 1399 Lisboa Codex, Portugal Received 17 March 1999; received in revised form 9 July 1999; accepted 16 August 1999 Abstract The effects of dietary fibre level 20–16–12 acid detergent fibre [ADF], without variations in the proportions of the fibre fractions hemicellulose, cellulose, lignin . . . , were studied with respect to many aspects of rabbit digestion ileal digestibility, transit, microbial activity, growth and health. For the lowest level of ADF, the voluntary intake of animals was reduced by 25 and weight gain by 9, during the two weeks postweaning 28–42 days, and there was a sharp increase P , 0.01 of morbidity between 42 and 70 days old. A linear reduction of the whole tract digestibility for OM was observed according to ADF level 21.6 unit per ADF, without significant changes in fibre digestibility. When ADF level passed from 20 to 12, ileal digestibility of organic matter increased from 38 to 61, while it decreased from 27 to 17 in the caeco-colic segment. Starch ileal digestibility was lowered by 5.7 units with the reduction of the ADF starch ratio, but remained at a very high level . 93. A sharp increase in mean retention time between ileum and rectum 1 38 was noticed, reaching 19 h for the lowest ADF level. The bacterial fibrolytic activity was significantly reduced with the lowest ADF level Fig. 1, and pectinolytic activity was more particularly affected 240. Two weeks after weaning the VFA level decreased linearly and significantly P , 0.01 with reduction of ADF level, while at 10 weeks no significant effect was observed.  2000 Elsevier Science B.V. All rights reserved. Keywords : Ileal digestion; Caecal microbial activity; Retention time; Rabbit; Dietary fibre

1. Introduction adapted to more concentrated feeds that are efficient-

ly digested in the upper segment of the tract ˜ As a monogastric herbivorous animal, the rabbit Carabano and Piquer, 1998. However, information exhibits a digestive physiology adapted to high on the partition of digestion between small intestine intake of dietary fibre DF which is fermented in the and caeco-colic segment is very scarce three studies hindgut caecum and proximal colon, but also only, and moreover does not relate digestion to rate of passage or caecal microbial activity CMA or with zootechnical performances. Therefore, we de- Corresponding author. Tel.: 133-56-128-5103; fax: 133-56- veloped a new approach to obtain more comprehen- 128-5319. E-mail address : gidennetoulouse.inra.fr T. Gidenne sive information on rabbit digestion, that combined 0301-6226 00 – see front matter  2000 Elsevier Science B.V. All rights reserved. P I I : S 0 3 0 1 - 6 2 2 6 9 9 0 0 1 4 1 - 4 226 T . Gidenne et al. Livestock Production Science 64 2000 225 –237 Table 1 measurements of parameters cited previously in a set Ingredients and composition of the experimental diets of experiments using a single and a simplified dietary Diets A20 A16 A12 model. A reduced fibre intake is known to increase the Ingredients incidence of digestive disturbances in the growing Wheat 12.0 32.0 50.0 Soya bean meal 9.7 13.7 17.5 rabbit Lebas et al., 1998. Digestive consequences Wheat bran 22.0 9.8 – of fibre are determined as well by the quantity of Dehydrated lucerne meal 24.0 17.0 9.0 dietary fibre consumed as by the degradability of cell Dehydrated beet pulp 25.0 19.5 15.0 wall components in relation to their physico-chemi- Wheat straw 6.0 6.0 6.0 a cal structure, such as particle size Gidenne et al., Minerals and vitamins 1.3 2.0 2.5 1991a. However, very few studies separated the Chemical analysis g kg air dry basis effect of the DF content from that of the nature of Organic matter 858 861 864 the cell wall, because complex dietary models were Crude protein Nx6.25 153 161 170 b often used. Thus in the present study, we studied Lysine 8.2 8.1 8.3 b only the effect of a fibre level reduction, without Sulphur amino acids 6.8 6.9 7.0 Starch 104 213 295 variations in the proportions of the different fibre Neutral-detergent fibre NDF 393 313 238 fractions cellulose, lignin, etc., and using an origi- Acid-detergent fibre ADF 202 155 117 nal comprehensive approach of rabbit digestion. Acid-detergent lignin ADL 36 28 21 b Water insoluble pectins 88 71 57 c NNCC 312 387 456 ADF starch ratio 1.9 0.7 0.4

2. Materials and methods