Effects of crude fibre level in the diet on the intestinal morphology of growing rabbits

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1 Effects of crude fibre level in the diet on the intestinal morphology of growing rabbits BiYu & PeterW. S. Chiou Department of Animal Science, National Chung-Hsing University, Taichung,Taiwan Summary The experiment was conducted to study the effects of 5.5, 8.5, 11.5 and 14.5% dietary fibre levels on growth performance and intestinal villi in growing rabbits. After the 5-week feeding period, food intake and body weight gain increased with increasing dietary fibre levels, feed conversion was highest with 11.5% dietary fibre. Scanning electron microscopy showed slight changes to the jejunal villi and the caecal mucosa in rabbits fed high dietary fibre (14.5%t but the degree of damage was greater in the caecum than the jejunum. Flattened colon villi were seen in the low dietary fibre group whereas high levels showed no effect. Keywords rabbit, dietary fibre, intestinal morphology, villi In herbivorous monogastric rabbits, extremely high levels of dietary fibre intake can have an adverse effect on the efficiency of feed utilization (Marty & Vernay 1984, Yu et al. 1985t but the mechanism is unclear. After long-term feeding of a high-fibre diet in rats, the absorption of nutrients was significantly decreased (Freeman 1984). Research on monogastric animals such as rat (Sig1eoet al. 1984, Sagher et al. 1991), pig (Moore et al. 1988) and monkey (Paulini et al. 1987) suggests that the mucosal structure and morphology in the small intestine are significantly influenced by the system of feeding, by the ingredients and particularly by the dietary fibre, i.e., cellulose, pectin and lignin. Chiou et al. (1994) suggests that differing degrees of intestinal mucosal damage in growing rabbits resulted from feeding differing levels of dietary fibre. Yamauchi & Isshiki (19911 found that broiler chickens developed larger intestinal villi with high dietary fibre Correspondence to: Dr P. W. S. Chiou, Department of Animal Science, National Chung-Hsing University, 250 Kuo-Kuang Road, Taichung, Taiwan, R.o.C. Telephone No: ; Fax No: Accepted 23 August 1995 levels which resulted in faster growth rates than layers. They also suggested that the development of the intestine is a major limiting factor on feed intake in poultry. The dietary fibre requirement in the domestic rabbit is 10 to 12% (NRC, 1977), and rabbits can only digest 14% ingested fibre (Maynard et al. 1979). The higher requirement of dietary fibre than other monogastric animals may be explained by its importance for the rabbit as a source of nutrition. Cheeke (1982)found a decrease in diarrhoea in rabbits on high dietary fibre but information concerning the effects of dietary fibre level on intestinal structure is unknown. The aim of this experiment was to investigate the effect of differing dietary fibre levels on the growth performance and the morphology of the large and small intestinal villi in rabbits. Materials and methods The experimental diets were formulated on isocaloric and isonitrogenic bases with different levels of dietary fibre, i.e. 5.5, 8.5, 11.5 and 14.5% according to the feeding standards of the NRC (1977)(see Table 1). Sixteen 4- week-old Californian male rabbits were Laboratory Animals (1996) 30,

2 144 Yu & Chiou Table 1 Composition of the experimental diets Level of dietary fibre, % Ingredients Ground corn Soybean meal Wheat bran Alfalfa meal Laterite Tallow Dicalcium phosphate Calcium carbonate L-Iysine DL-methionine Salt Premix* Analysed values, % Crude protein Gross energy, Meal/kg Calcium Phosphorous Crude fibre *Premix components per kg of diet: CuS04.5H mg; FeS04.7H mg; 2nS mg; MnS04.5H mg; Choline chloridel g; Vitamin mg; Vitamin mg; Niacin 200 mg; Vitamin E 50 mg randomly allocated into 4 treatment groups with 4 animals in each treatment. Bodyweight gain and feed intake were measured for the 5-week feeding period and then all rabbits were killed. Intestinal samples (3 cm) were taken from different segments of the intestine: jejunum (20 to 80% distance from the duodenum), caecum and colon. All samples were rinsed with 0.4 M Kel, and 0.5 cm taken with a sharp knife for scanning electron microscope [SEM) according to the method of Paulini et 01. (1987) and modified by Moore et 01. (1988). All gut samples were fixed initially in 10% buffered formaldehyde ph 7.0; then the specimens were washed (0.1M phosphate buffer ph 7.3, 3 times for 10 min), and placed in 1% osmium tetroxide overnight. These samples were washed again (phosphate buffer 4 times for 15 min) and then gradually dehydrated increasing alcohol concentrations: 50, 70, 80, 90 and 95% for 10 to 15min each time until finally, the concentration was increased to 100%-3 x. Specimens were then subjected to critical point drying mounting on aluminium stubs, coating with gold for half an hour Table 2 Effect of the levels of dietary fibre on the mean performance of the growing rabbits Level of dietary fibre, % Items Averaged initial weight, g 1210± ± ± ±125 Averaged final weight, g 1899±S3 a 2030±229 b 2010±147 b 2243±204 b Averaged weight gain*, g 689±116 a 825±145 b 923±82 b 900±106 b Averaged feed intake*, g 2900±100 a 3120±120 b 3260±140 b 4300±13S c Feed conversion g feed/g gain 4.22±0.82 b 3.78±0.53 ab 3.53±0.42 a 4.78±0.39 bc *The body weight gain and the feed intake are the average of the thirty-five days feeding period a,bvalueswithin the same row with the same subscript letters are not significantly different (P< 0.05)

3 Dietary fibre and rabbit intestinal morphology 145 Fig.1 Scanning electron microscopic photograph of a normal rabbits' jejunum across the treatment groups with finger-like villi (a, 100x; b, 250 x); tongue-like villi (c,100x; d, 250 x) and placed in the SEM (Bausch & Lomb Ltd., Nonolab 2100) for scanning. Samples were analysed blind and an analysis of variance was made (Statistical Analysis System 1985). any significant trend of dietary fibre on morphology of the villi, although damaged and dead epithelial cells were seen on the jejunal villi of 2 rabbits in the group fed 14.5% fibre (Fig. 2). Results The results are presented in Table 2. It can be seen that the bodyweight gains and the feed intake were significantly increased as the level of dietary fibre increased from 5.5% to 14.5% (P< The level of dietary fibre also significantly influenced the efficiency of feed utilization of the growing rabbits (P<0.05). Morphological changes in the jejunum The intestinal morphology of the jejunum: showed great variation between individuals, some showed a narrow finger-like (Fig. la & Ib), whereas others showed broad tongue-like villi (Fig. lc & Id). There did not appear to be Fig.2 Scanning electron microscopic photograph of the jejunum in a rabbit fed 14.5%high dietary fibre (250 x)

4 146 Yu & Chiou a more rapid rate of passage judged from averaged feed intakes (P<O.05j. Since the experimental diets were isocaloric and isonitrogenous, any increase in feed intake represents an increase in the intake of energy and protein. This was reflected in the bodyweight gains and explains the poor performance of animals on the lowest level of dietary fibre. Narrow and long villi indicate a faster multiplication of the base of the crypt which migrated faster to the tip of villi and the turnover of the epithelial cells would, therefore, be shorter (Nordstrome & Dahlqvist 1973). This rapid turnover causes an incomplete DNA synthesis in the cells, which consequentially show irregular shapes and immature epithelial cells (see Gordon et al. 1993). Broader villi on the other hand, provide a greater surface area and, therefore, more Fig.3 Scanning electron microscopic photograph of the caecal mucosa in rabbits fed 5.5, 8.5 or 11.5% dietary fibre (a), and 14.5% dietary fibre (b) Morphological changes in the caecum and colon The SEM showed normal growth and development of the mucosa and normal goblet cell distribution in the caecal mucosa of rabbits fed diet 5.5, 8.5 or 11.5 % dietary fibre (Fig. 3al, but damaged caecal mucosa cells were observed on 14.5% (Fig. 3b). The effect of low dietary fibre level 15.5%1 on the colon (Fig. 41 showed a flattened mucosa, other groups showed little effect. Discussion During on low eat and groups, the experimental period, the rabbits dietary fibre (5.5%) often refused to wasted more feed than the other whereas the high dietary fibre group (14.5%1 showed a better appetite and possibly Fig.4 Scanning electron microscopic photograph of the colonic mucosa in a rabbit showing a flattened mucosa (a), and a damaged mucosa (b)

5 Dietary fibre and rabbit intestinal morphology 147 brush border (Yamauchi & Isshiki 1991). Due to the large variation of the intestinal villi in this trial, it was not impossible to correlate the intestinal morphology with growth performance. Damaged villi were seen in the high dietary fibre fed rabbits but the damage was only slight. This phenomenon has been shown also in the pig (Moore et al. 1988).It is not clear how the significant low efficiency of feed utilization in the high dietary fibre group was related to the damaged villi. Stachithandam et al. (1990)also suggested an influence of high dietary fibre in the rat where they found an increase in the number of goblet cells, in the mucin secretion, and in the density of the luminal contents, all of which could lead to a decrease in the absorption of nutrients. It appears that dietary fibre does not significantly influence the intestinal morphology of the domestic rabbit. On the other hand, we have shown a significant influence of different fibre components on the mucosal cells (Chiou et al. 1994) as have others (African green monkey and rat, Paulini et al. 1987, Johnson et al respectively). Diets with low dietary fibre contain more soluble carbohydrates which would be digested before reaching the caecum in rabbits (Graham et al. 1986)resulting in less effed on the caecal mucosa. On the other hand, high dietary fibre could greatly influence caecocolic motility (Bouyssou et al. 1988). This movement could bring fibre back into the caecum (Bjornhag 1972) and the fine fibre particles could provide a source of substrate for fermentation leading to the formation of volatile fatty acids and toxins. This fermentation could also produce hydrogen ions that would increase the rate of cell division (Lupton et al. 1988)and cause the histological changes seen in the intestine, e.g. damaged caecal mucosa. Gidenne (19921 suggested that the reduced retention time caused by the increase in dietary fibre originated mainly from the caecum and rectum rather than the stomach and small intestine. He showed that the enlargement of the digestive organs of the distal part in the tract would contribute to a higher fibre degradation. Paulini et al. (1987) observed slight damage to the colonic mucosa of psyllium-fed African Green Monkeys thought to be due to the slow passage and longer physical contact time of the diet with the intestinal wall, leading to thinner mucosal cells. Yu et al. (1985)showed a significant slower rate of passage in rabbits on low fibre diets and that the capacity of the caecum and colon was increased in the rabbits on high fibre diets. High dietary fibre in rabbits, therefore, will not only prevent diarrhoea caused by the abnormal intestinal fermentation, but also improve feed intake. Acknowledgments The authors thank the Nation Science Council in Taiwan, Republic of China, for the financial support of this project. The project number is NSC 81-01l5-C B & 027B. Authors also acknowledge K. C. Huang and W. J. Huang for their assistance in the trial. References Bjornhag B (1972) Separation and delay of contents in the rabbit colon. Swedish TournaI of Agricultural Research 28, Bouyssou T, Candau M, Ruckebush Y (19881 Colonic motility pattern according to the source of fibre and to the grinding level of the diet in the rabbit. Reproduction Nutrition Development 28, Cheeke PR (1982) High roughage diets utilisation by rabbits. Feed International 3, Chiou PWS, Yu B, Lin C (19941 Effect of different components of dietary fibre on the intestinal morphology of domestic rabbits. Comparative Biochemistry and Physiology I08A, Freeman HJ (1984) Amino acid and dipeptide absorption in rats fed chemically defined diets of differing fibre composition. Canadian TournaI of Physiology Pharmacology 62, Gayne CM, Acton JC (1983) Fibre constituents and fibrous food residue effects on the in vitro enzymatic digestion of protein. Journal of Food Science 48, Gidenne T 11992) 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. British TournaI of Nutrition 67, Gordon DT, WilWord K, Ellersieck MR 11983) The action of cellulose on the intestinal mucosa and element absorption by the rat. TournaI of Nutrition 113, Graham H, Hesselman K, Aman P (1986) The influence of wheat bran and sugar-beat pulp on the digestibility of dietary components in a cereal base diet. TournaI of Nutrition 116, Hsu HC, Penner MH (19891 Influence of cellulose structure on its digestibility in the rat. TournaI of Nutrition 119, 872-8

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