The effect of manipulation of pellet size (diameter and length) on pellet quality and performance, apparent metabolisable energy and ileal nutrient digestibility in broilers fed maize-based diets

A 2 by 2 factorial arrangement of treatments was used to evaluate the effect of pellet diameter (3 and 4.76 mm) and pellet length (3 and 6 mm) on pellet quality and performance, apparent metabolisable energy and ileal digestibility of nitrogen and starch in broilers. From 0 to 9 days of age, all birds were offered a common starter diet. Broiler grower (Days 10–21) and finisher (Days 22–42) diets, based on maize, were formulated and then allocated to the four different treatments. All diets were steam-conditioned at 60°C before pelleting. In grower diets, increasing pellet diameter and pellet length reduced (P < 0.001) the gelatinised starch content of the diets. In finisher diets, gelatinised starch content of pellets was not influenced (P > 0.05) by main effects or the interaction. In grower and finisher diets, increments in pellet durability index and pellet hardness with increasing pellet length were greater in pellets with a 3-mm diameter than those with a 4.76-mm diameter. During the grower period (Days 10–21), birds fed the 3-mm-diameter pellets had lower (P < 0.01) feed per gain than those fed pellets with a 4.76-mm diameter. During the finisher (Days 22–42) and whole trial (Days 10–42) periods, neither main effects nor the interaction were significant (P > 0.05) for weight gain, feed intake and feed per gain. Increasing pellet diameter from 3 to 4.76 mm decreased (P < 0.001) apparent metabolisable energy values. Neither main effects nor the interaction were significant (P > 0.05) for the coefficient of ileal apparent digestibility of nitrogen. Increasing pellet length from 3 to 6 mm decreased (P < 0.05) relative weight of gizzard in 3-mm-diameter pellets but not in the 4.76-mm-diameter pellets (P > 0.05). Overall, when low conditioning temperatures are used to optimise nutrient availability, small diameter die holes and longer pellet lengths can favour creating high physical quality pellets. The present study also showed that feeding lower diameter pellets to broilers during the grower period (Days 10–21) only improved feed per gain, a response which disappeared as the birds grew older.