Body and intestinal growth of broiler chicks on a commercial starter diet.1. Intestinal weight and mucosal development

1. A study was conducted on the pattern of development of the intestinal mu cosa of the Steggles x Ross (F-1) strain of broiler chickens reared on a co mmercial starter diet. The mechanisms underlying the structural changes wer e also assessed. 2. In relation to body weight, small intestinal weight peaked at 7 d of age and declined subsequently. There was also a reduction in the relative weig hts of the gizzard and yolk sac with age. The length of the small intestine and its regions increased with age. 3. Crypt depth increased with age in the duodenum and jejunum while villus height increased significantly with age in all three regions of the small i ntestine. There were also significant changes in apparent villus surface ar ea in the three regions, while interactions between age and intestinal regi on were significant in the case of crypt depth and villus height. 4. There were significant differences between the age groups in the mucosal protein content of jejunal and ileal homogenates, both tending to peak at 7 d of age. The DNA content of the intestinal mucosa declined with age in t he three regions of the small intestine. While there was an increase in RNA content in the duodenum and ileum, there was a reduction in the jejunum. 5. Protein : DNA ratio increased between hatch and 21 d of age in all intes tinal regions. Protein : RNA ratio decreased with age in the duodenum and i leum but increased in the jejunum. There were significant increases in RNA : DNA ratio in the duodenum and ileum but no changes were observed in the j ejunum. The interactions between age and intestinal region were significant for all biochemical indices assessed. 6. At all ages, enterocyte proliferation at the jejunum was completed and q uantifiable within 1 h of administration of 5-bromo-2'-deoxyuridine (BrDU). Subsequent assessment revealed an increase in crypt column count and numbe r of BrDU-labelled cells. The rate of cell migration increased with age whi le there was a decline in the distance migrated in proportion to mucosal de pth. The estimated life-span of enterocytes and time spent by enterocytes i n the crypt varied with age. In d-old and 7-d-old chicks, migration was com plete or nearly complete within 96 h of cell birth. 7. Although the intestinal mucosa of the strain was structurally developed at hatch, there was much change in structure with age, especially over the first 7 d post hatch. The rate of development was most rapid in the jejunum but the other regions are also important, on account of villus height or r elative length of the region.