| An experiment was conducted to test the directionality, scaling and reversibility of phenotypic responses of different organ and muscle groups of ganders in response to rice husk (RH) diluted dietary switching. Ninety-six 140-d-old ganders were acclimatized to the basis diet for 2 weeks. The birds were randomly assigned to 4 treatments. Each treatment was represented by 4 replicates containing 6 ganders (24 birds per treatment). At day 1, diets in experimental groups were switched from the basis diet to diets which contained 20%, 40% and 60% RH by mass, with no RH in the basis diet. After 21 days, two birds of each replicate were killed, and their size changes in different organ and muscle groups were studied. The diet of all the experimental birds was switched back to the basis diet until day 42, when a further two birds from each replicate was killed, and their size changes in different organ and muscle groups were studied, too. The results indicated that,1. Increased feed intake was observed with increasing RH content in the diet in the 1st week, which was significantly more than those in the control group (P<0.05). In the 2nd and 3rd week, feed intakes in 20% and 40%RH groups increased few compared that in the 1st week, while a gradually increasing trend was found in feed intake in 60% RH group (week 1-3: 380g, 447g, 510g), which was obviously higher than at low RH levels(P<0.05). A decreased trend appeared after diet-switching (P<0.05). A decrease, then an increase, and then a decrease were appeared in feed intakes in 20% and 40%RH groups. In the 4th week of the experiment, feed intakes in 20% and 40%RH groups decreased (64.4% and 52.6% of the 3rd week respectively). In the 5th week, the feed intakes were a little higher than that in the control group (16.7% and 17.3% higher than at control group). What is more, feed intake in the 60% RH group decreased unremittingly (week 4-6: 250g, 232.7g, 201.2g). In the 4th and 5th week, the feed intake was higher than that in the control group, while there was no significance between them in the 6th week. It was indicated, in part, that geese have unique character of nutritional requirement. Comparing with chicken and ducks, geese can be fed with diet containing lower levels of nutrition or higher levels of crude fiber.2. The weights of geese fed 60 % RH diet for 21 days reduced, and were significantly less than those of the other three groups (P<0.05). And the relative weight of abdominal fat was lower than at 20%RH group. The fat content of liver and thigh in the 20%RH group was highest, amongst which, liver fat was higher than at 40% and 60%RH groups, gizzard fat was higher than at 60%RH group. No significantly difference was observed in the relative weight of eviscerated carcass, breast, thigh, heart and liver. Body weights (BW) of the geese in all groups increased after diet-switching back to the basis diet, and no significant difference was noted in BW among them after a further 21 days. However, the relative weight of thigh in birds fed 40 % RH diet were improved compared with birds receiving basis or 20% RH diet (P<0.05). The relative weight of heart in the 20% and 40%RH groups were less than that in the control group, and the relative weight of pancreas in 40%RH group was smallest. No significantly difference was observed in other values. It was appeared that, appropriate amount of rice husk in the diet can meet the growth needs of the ganders, and can improve the meat quality to some extent.3. At day 21, heavier relative weights of glandular stomach, gizzard and all gut components were observed in birds fed 60% RH diet (P<0.05), and heavier relative weight of gizzard was observed in birds given 40% RH diet (P<0.05). What is more, thickness of the two gastric walls, gizzard and all gut components relative length had increased in birds given 60% RH diet compared with the other three groups (P<0.05). At day 42, no significant difference was noted in the relative weights and lengths of gastrointestinal tract, except for caecum which was heavier and longer in birds fed 60% RH diet (P<0.05). At day 21, a decreased trend was found in the villus height and crypt depth of duodenum, an increased trend was found in the crypt depth of jejuna. The crypt depth of jejuna in 60% RH group was obviously bigger than that in the 20% RH group. The crypt depth of duodenum in the 20% RH group and jejuna in the 60% RH group were improved compared with those in the control group (P<0.05). At day 42, the villus height of jejuna in the 20% RH group increased significantly than at control group, and the crypt depth of jejuna in the 60% RH group was biggest compared with the other groups. The peak of villus height appeared in the 20% or 40%RH group, and the peak of crypt depth was found in the 60% RH group.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. Additionally, size responses were reversible, and reduced RH was followed by a decrease of gastrointestinal tract size.
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