Effects of fasting and refeeding on structures of the intestinal villi and epithelial cells in White Leghorn hens

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Abstract
1. The fine structural alterations of villi and epithelial cells in each part of the small intestine were investigated in layer‐type hens fasted for 12 h to 20 d or refed for one day after each fasting period. 2. Within the first 24‐h‐fasting, villi of the duodenum showed a remarkable reduction in height and those of the jejunum revealed a gradual decrease; such a significant reduction of the villus height was not obtained in the ileum. After 36‐h‐fasting, villus height in each part gradually decreased with days of fasting. 3. All intestinal villus heights increased after only 1‐d‐refeeding of various kinds of diets following 3‐, 10‐, or 20‐d‐fasting. The duodenum especially rapidly recovered even after long‐term fasting of 20 d but the ileum showed very slow recovery, suggesting that the ileum seems to be inactive in absorptive function. 4. These variable alterations of villus height in the proximal intestine suggest that the higher intestinal absorptive ability is under the normal feeding, the more rapidly villus height is influenced by nutritional conditions. 5. Cell area and cell mitosis decreased after fasting, the latter showing a marked reduction. However, in spite of a remarkable decrease of cell mitosis in the proximal intestine after fasting, refeeding activated cell renewal and it soon reached control levels, demonstrating that the villus height mainly varied with the numbers of epithelial cells. 6. In the epithelial cells of the proximal intestine in chickens fasted for 20 d, large lysosomal autophagous vacuoles including mitochondria and dense bodies were observed. These were reduced in size by refeeding for only one day, suggesting that fasting may cause intracellular digestion through lysosomal autophagy. 7. These results lead to the conclusion that long‐term fasting for force moulting is possible, that a high protein and high energy diet can be fed immediately after fasting and that a cell undergoing lysosomal autophagy in normal chickens indicates undernutrition.