Fibrous feeds for functional fowls
Abstract: Fibres are not digested by fowls, but their impact on digestive physiology, nutrient metabolism and intestinal microflora can be substantial. Analytical shortcomings have historically contributed to different notions on the significance of fibres, but modern techniques now enable us to better discriminate between various fractions of fibre and relate them with the performance of poultry. The four present studies examined relationships between different qualities and means of providing fibres, and the functionality of broiler chickens and laying hens. In broiler chickens, increasing the dietary levels of insoluble fibres stimulated fat and protein digestion, but not in a dose-dependent manner. In the small intestine, these effects were mirrored in altered tissue morphology and luminal microflora composition. Moreover, addressing the negative effects of soluble fibres in wheat on digestion by adding a xylanase to the diet improved feed utilization. These effects were not mirrored by macroscopic or microscopic changes of the small intestine. Effects similar to those of the xylanase were achieved by adding a protease, but not a coccidiostat, to the diet. There were no signs of the effects of the two enzymes being additive. In laying hens, supplementary roughage reduced beak-inflicted injuries and improved feed efficiency; the latter finding likely reflecting better plumage conditions. Increased dietary levels of fibres and fat reduced the liver fat and tended to improve feed efficiency; the latter result probably explained by beneficial effects of added fat on digestion. The diet with more fat and fibres also impaired the hygienic conditions in the stable, presumably due to the fibre fraction being mainly soluble in nature. Experimental lines of hens predisposed to perform severe feather pecking preferred a diet supplemented with spelt hulls more than corresponding hens not predisposed to perform severe feather pecking. This finding supported previous indications that injurious pecking correlates with the fibre content of the feed. It was concluded that the significance of fibres in poultry nutrition largely depends on the quality of fibres. Whereas soluble fibres primarily acted detrimentally on the functionality of the birds, insoluble fibres tended to act in the opposite direction. In poultry nutrition experiments, however, it remains difficult to separate the effects of increasing amounts of fibrous feedstuffs from those of simultaneous dietary fat supplementation, nutrient dilution or ingestion of fibrous materials such as litter.
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