Effect of grinding method and extent of pelleting of broiler diets on performance, feeding behaviour and digestive tract functionality.

1. An experiment was carried out to examine if a heterogeneous diet consisting of pellets and coarse cereal particles would result in a similar feed intake to pelleted-only diets. It also considered whether coarser particles entering the gizzard would encourage the development of the gizzard and thus improve digestive tract functionality. Maize and wheat were hammer milled through a 3 mm screen after coarse grinding using either one of the two screens with a novel pattern. Three pellet-only diets were produced based on three grinding sizes. Additionally, four diets were produced by separating coarse cereal particles from moderately coarse particles by sieving either once or twice, pelleting the remainder and finally mixing these into a complete heterogeneous diet.2. No difference in performance between birds fed the three pelleted-only diets was observed. However, heterogeneous diets resulted in a lower feed intake (FI) and weight gain (WG) than pelleted-only diets (p < 0.05). The dietary treatments neither affected the feed conversion ratio nor ileal digestibility of starch and protein (p > 0.05). As expected, feeding a heterogeneous diets increased (p < 0.05) the relative weight of the gizzard and its contents. Approximately 50% of the particles in the small intestine were between 0.15 mm and 0.36 mm in diameter, with more fine particles observed when the pelleted-only diets containing coarsely ground cereals were fed, confirming the capacity of the gizzard to finely grind feed.3. Sieving of the diet remaining in the feeder during 4 h of feeding two of the heterogeneous diets showed that the particles > 2.8 mm disappeared first (p < 0.05), showing the birds' preference for larger particles when offered heterogeneous diets. Although the birds were able to handle the coarse microstructure of the diets without any negative effects, the reduced performance in the case of heterogeneous diets might have been related to feed intake issues and particle selection, resulting in an imbalance in nutrient intake.