Influence of conditioning temperature on performance, apparent metabolisable energy, ileal digestibility of starch and nitrogen and the quality of pellets, in broiler starters fed maize- and sorghum-based diets

The influence of conditioning temperature on performance, apparent metabolisable energy (AME), ileal digestibility of starch and nitrogen and the quality of pellets, in broiler starters fed maize- or sorghum-based starter diets were examined in this study. The experimental design was a 2 × 3 factorial arrangement of treatments evaluating two grain types (maize and sorghum) and three conditioning temperatures (60, 75 and 90 °C). Broiler starter diets, each based on one grain (maize or sorghum) were formulated and pelleted at the three temperatures. Birds fed diets conditioned at 60 °C had a similar weight gain to those fed diets conditioned at 90 °C and higher (P<0.01) than those fed diets conditioned at 75 °C. Birds fed diets conditioned at 60 and 90 °C tended (P=0.07) to have higher feed intake than those fed diets conditioned at 75 °C. Conditioning temperature had no effect (P>0.05) on feed per unit gain. Pellet hardness increased (P<0.001) with increasing conditioning temperatures, particularly at 90 °C. Increasing conditioning temperatures caused gradual improvements in the pellet durability index of maize-based diets, while the improvement was marked in the sorghum-based diet conditioned at 90 °C. In maize-based diets, the coefficient of ileal apparent digestibility (CIAD) of nitrogen was significantly (P<0.05) poorer at 75 °C compared with 60 and 90 °C whereas the CIAD of starch was unaffected (P>0.05) by conditioning temperature and AME was optimized at 75 °C compared with 60 and 90 °C. For sorghum-based diets, increasing conditioning temperatures resulted in linear reductions (P<0.05) in the CIAD of nitrogen and starch and AME. Increasing conditioning temperatures increased (P<0.001) the relative gizzard weights in both diet types. Overall, these results suggest that the effect of conditioning temperatures on broiler performance is determined through their counteracting influence on nutrient availability and pellet quality.