Varying starch to fat ratios in pelleted diets: II. Effects on intestinal histomorphometry, and short-chain fatty acids in -challenged broiler chickens.

1. The hypothesis behind the study was that a high dietary starch level (HS) would lead to impaired gut health compared to a low-starch diet (LS) in -challenged broilers. The effects of two diets with different starch to fat ratios on intestinal histomorphometry, counts and toxin profile, necrotic enteritis prevalence and abundance of short-chain fatty acids (SCFAs) were examined. 2. A total of 1,920 one-day-old Ross 308 broiler chickens were fed one of two isocaloric diets formulated either with high (32:1) or low (2:1) starch to fat ratios from d 10 to 29 of age. Each treatment group had 12 pen replicates containing 80 broilers each. On d 17, the chickens were challenged with vaccine strains. Samples were collected on d 16, 21-23 and 29. 3. Whereas villus length increased gradually throughout the study in the HS group, a peak level was reached on d 21-23 in the LS group. On d 29, the HS group had significantly longer villi than the LS group. 4. Caecal SCFA concentrations were higher in the HS group compared to the LS group on d 16. In both groups, the SCFA level peaked on d 21-23, with the most pronounced increase seen in the LS group. 5. The ratio increased from d 16 to 29 in the HS group. counts and necrotic enteritis prevalence were similar between the two groups. 6. Diet affected the dynamics of small intestinal villus length and caecal SCFA abundance. These findings suggest that structural remodelling of the small intestine is an adaptation to different dietary starch levels, and that caecal SCFA abundance is associated with the availability of substrate for the microbiota in the posterior intestinal segments. Chickens adapted to higher levels of dietary starch might be more robust against infections due to increased mucosal surface area. Studies with other dietary starch sources are required to clarify the impact of dietary starch levels on intestinal health in -challenged broilers.