The effect of ratio of oats with hulls (OWH) to dehulled oats (DO), extent of grinding, and their interaction on the performance, gizzard characteristics and intestinal health of broilers chickens were studied in this experiment. A total of 2860 one-day-old male broilers were allocated to 130 floor pens bedded with wood shavings and fed a starter diet until day 10. On day 11, the birds were randomly distributed among ten dietary treatments (13 replicates each), consisting of five oat-based pelleted diets with different proportion of OWH and DO, and with main ingredients either finely- (2 mm) or coarsely-ground (6 mm). Half of a batch of oats was thoroughly dehulled and half kept as is. The content of hulls (OH) in the DO and OWH was 1 and 224 g/kg, respectively. Using different OWH:DO ratios, the diets were formulated to contain 0, 29.5, 65.0, 96.0 and 114.0 g/kg OH. The ratio of ingredients to DO, and apparent metabolisable energy to protein (AME:CP) were kept constant for all diets. Birds and feed were weighed on day 11 and at termination on day 32. Increasing OH level did not affect weight gain (WG) from 11 to 32 days, but increased FCR linearly (P < 0.001). Although FI was not affected by the extent of grinding, FCR was significantly improved with fine grinding. Birds fed diets with highest OH level had a lower AME:WG compared to those given diets with DO only. Coarse grinding significantly increased gizzard dry matter (DM) weight which also increased linearly (P < 0.001) with increasing OH level. Coarse grinding as well as increasing OH level significantly improved gizzard and pancreas relative weights and decreased gizzard contents pH. Excreta DM contents and litter score were significantly improved with increasing OH level. Coarse grinding tended to (P = 0.069) reduce total eubacteria density in the ileum only at the highest OH level and tended to (P = 0.080) reduce Lactobacillus spp. density compared to fine grinding. Increasing OH level had no impact on caecal short chain fatty acids or lactic acid production, but it decreased indole concentration linearly (P = 0.026). Coarse grinding tended to increase (P = 0.053) caecal propionic acid production. Importantly, broiler chickens were able to handle an OWH-based diet and still maintained a similar WG compared to diets with DO only. A larger gizzard holding capacity and a faster passage of excess OH may explain the ability to increase FI in response to high OH dilution.
