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Abstract
1. An experiment was conducted to test the directionality, scaling and reversibility of phenotypic responses of the gastrointestinal tract (GIT) of adult ganders to rice husk (RH) diluted dietary switching.
2. A total of 96 140-d-old ganders were acclimatised to a basal diet for 2 weeks. The birds were randomly assigned to 4 treatments. On d 1, diets in the experimental groups were switched from the basal diet to diets which contained 200, 400 or 600 g/kg RH by mass, with no RH in the basal diet. After 21 d, the diet of all the experimental birds was switched back to the basal diet until d 42.
3. Increasing RH content significantly increased feed intake, and a decreased trend appeared after diet-switching. The weights of geese fed on the 600 g/kg RH diet for 21 d reduced, and were significantly less than those of the other three groups, while body weights (BW) of the geese in all groups increased after diet-switching back to the basal diet. At d 21, significantly heavier relative weights of proventriculus, gizzard and all gut components, except duodenum, were observed in birds fed on a 600 g/kg RH diet, and significantly heavier relative weights of gizzard were observed in birds given a 400 g/kg RH diet. Thickness of the two gastric walls, gizzard length and all gut components lengths increased significantly in birds given a 600 g/kg RH diet compared with the other three groups. At d 42, no significant differences were noted in the relative weights or lengths of GIT, except for the caeca, which were significantly heavier in birds fed on 600 g/kg RH diet.
4. The results of the experiment were in accordance with the predictions of the hypothesis that there is matching between loads and capacities. The observed phenotypic responses were directional and scaled to the demands.
Acknowledgements
This work was financially supported by National Technology System of Waterfowl Industrial (nycytx-45-22), and Scientific and Technical Support Program of Jiangsu Province (BE2009351), P.R. China.