The effect of grinding method and extent of pelleting of broiler diets on performance, feeding behavior, and digestive tract functionality

Abstract

Two experiments were conducted for the accomplishment of this thesis. The grinding experiment was carried out with several normal screens and novel screens to study the effect on particle sizes. Grinding with novel screens was satisfactory for the coarser grinding. Based on the results of the grinding experiments, a 3 mm normal screen and two novel screens were selected for the production of wheat and maize-based seven experimental diets. Broiler experiment was carried out with the hypothesis that it would be possible to increase the microstructure for proper gizzard development and at the same time macrostructure to assure the feed intake is not compromised. Three diets were pelleted (SP, VCP, and MCP) from each grinding level and the remaining four heterogeneous diets (VCPM1, VCPM2, MCPM1, and MCPM2) were the mixture of coarse cereals with the pellets. Ground cereals were initially sieved at two distinct levels (one and two sievings) for heterogeneous diets, and the resultant fines were then subjected to pellet production while coarse particles were then blended with pellets afterward. Particle size distribution of the pelleted-only diets showed that the percentage of coarse particles > 1 mm decreased after pelleting compared to the mash particle size. Feeding pelleted-only diets did not affect feed intake and weight gain. There was no consistent effect of heterogenous diets on feed intake and body weight gain, however, the tendency was lower for heterogeneous diets. None of the dietary treatments had an impact on FCR (P > 0.05). Relative gizzard and content weight increased (P < 0.05) with the inclusion of the heterogenous diets compared to the standard pelleted diet. The starch and protein digestibility between the treatments did not differ significantly (P > 0.05). In comparison to the moderately coarse cereals mixed with pellets after one sieving, the standard pelleted diet had a larger percentage of litter in the gizzard. Feeding behavior showed that birds spent more time eating diets MCPM1 and MCPM2 compared to the MCP. Feed preference trial showed that big particles > 2.8 mm disappeared first showing birds' preference for pellets when offered heterogeneous diets. When represented as D10, D50, and D90, the intestinal particle size determined by laser diffraction showed no significant change (P > 0.05) in any of the small intestinal segments. More than 50% of the particles in the duodenum are smaller than 0.1 to 0.2 mm, while 50 % of the particles in the jejunum and ileum are below 0.2 to 0.5 mm (200 µm to 500 µm) when expressed as a volume percentage. In both VCP and VCPM2-fed birds, excreta examination revealed that around 10% of the particles were larger than 1 mm. Overall, this experiment indicates that coarser grinding will result in less energy consumption and higher grinding capacity. Poor feed intake and weight gain were observed when fed heterogenous diets while a positive response was observed in terms of gizzard development and particle size distribution in the intestinal contents indicating that there is sufficient space for increasing both micro- and macrostructure in broiler diets. Therefore, diet selection can be a major limiting factor to broiler performance.