The present study was undertaken to provide detailed information about the effect of fibre source (pea fibre, wheat bran or oat bran) at inclusion levels of 0, 187 and 375 g/kg diet on the development of the digestive tract, nutrient digestibility and energy and protein metabolism in broiler chickens. Heat production was measured using open-air-circuit respiration chambers. Diets with increasing levels of pea fibre decreased the DM in droppings and increased excreta output (2·5-fold) relative to DM intake. Adaptation to increased dietary fibre levels included increases in the size of the digestive system, with pea fibre exerting a stronger impact than wheat bran or oat bran. The length of the intestine, and particularly the length and weight of the caecum, increased with the fibre level. The digestibility of all nutrients also decreased with increasing fibre level. The decrease in the digestibility in relation to NSP for the three fibre sources was bigger for oat bran (0·0020 per g dietary NSP) than for pea fibre and wheat bran (0·0014 and 0·0016 per g dietary NSP) indicating that the cell walls in oat bran (aleurone and subaleurone) had a significant negative effect on the digestibility of cellular nutrients, i.e. protein and fat. The degradation of the NSP constituents was far lower in chickens than found in other animal species such as pigs and rats, thus supporting the view that chickens do not ferment fibre polymers to a great extent. Excretion of organic acids (mainly lactic acid and acetic acid) accounted for up to 2% of metabolizable energy (ME) intake with the highest excretion for the high-fibre diets. H2 excretion was related to the amount of NSP degraded and indicated higher microbial fermentation with increasing fibre levels. The chickens' feed intake responded to a great extent to dietary ME concentration but expressed in terms of metabolic body size (W0·75) ME intake was depressed at the high fibre levels. Dietary NSP was able to explain between 86% (oat bran) and 96% (pea fibre) of the variation in ME concentration. The amount of energy available from fermentation of NSP appears to reach a maximum of 42 KJ/d independent of fibre source and level. Expressed in relation to ME intake the NSP fermentation contributed 3-4%. With increasing fibre intake the partitioning of retained energy between body protein and body fat changed in favour of protein.

The present study was undertaken to provide detailed information on the effect of dietary fibre (DF) level on body composition, visceral organ weight, nutrient digestibility and on energy and protein metabolism of rats housed in cold (16°), warm (24°) or hot (32°) thermal environments. High- or low-fibre diets (257 v. 56 g DF/kg dry matter (DM)) were studied in a 6-week balance experiment (initial body weight about 100 g). Heat production was measured using open-air circuit respiration chambers. Pea fibre and pectin were used to adjust the DF level in the high-fibre diet. The ranking order of daily gain of rats kept in different environments was: 24°>16°>32°, while the ranking order for carcass protein was: 16°>24°>32°. Rats on the high-DF diet had a lower daily gain than those on the low DF diet, and more protein in DM of empty body weight (EBW) and less fat. The relative weights (g/kg EBW) of liver, heart and kidney decreased when increasing the environmental temperature. The relative weight of the heart was highest in rats on the high DF level, while liver and kidney weights were unaffected by DF. Per kg EBW, the stomach, small intestine, caecum and colon and the length of colon were significantly greater in rats consuming the high-fibre diet compared with those on the low-fibre diet. Rats kept at low temperature had a significantly heavier gastrointestinal (GI) tract than those kept at the highest temperature. Digestibility of protein, DM and energy was lowest for rats fed on the high-fibre diet. Heat production (HP) of fed rats as well as fasting HP decreased significantly as environmental temperature increased. HP as a proportion of metabolizable energy (ME) was significantly lower for rats at 24° compared with the other environmental temperatures. The proportion of energy retained as protein was slightly higher in rats fed on the high-fibre than on the low-fibre diet. Based on the results of the present study the authors measured a net energy value of 5·4 kJ/g DF fermented; approximately 50% of the DF came from peas. Possible implications of the present findings are discussed.