Increasing mixer-added fat reduces the electrical energy required for pelleting and improves exogenous enzyme efficacy for broilers

Abstract

The prices of fat and diet formulations with exogenous enzymes have caused a reduction in the amount of fat added to broiler diets. Although diets may be cheaper to produce, there is potential for nutrient and exogenous enzyme destruction with low inclusions of fat (0.5 to 1%) because of frictional heat and shear forces produced in the pellet die. Additionally, much of the added fat may be applied by using postpellet spray application, and the amount of fat added in the mixer may become negligible. Thermal inactivation of exogenous enzymes and the occurrence of unfavorable reactions (e.g., Maillard reaction, protein cross-linking) may be abated by increased levels of fat included at the mixer before pelleting [i.e., mixer-added fat (MAF)]. In this study, we evaluated the effects of MAF (1, 2.5, or 4%) with or without the addition exogenous enzymes (carbohydrase, protease, and phytase), and at different conditioning temperatures (82 or 85°C), on finisher phase feed manufacture, broiler performance variables, and processing yields. Increasing MAF reduced the electrical energy usage required to manufacture broiler feed (P < 0.02). Feed intake during the grower and finisher phases and live weight gain during the finisher phase were increased with enzyme addition (P < 0.001). Enzyme addition, conditioning temperature and MAF interacted in their effects on FCR from 23 to 38 d of age (P = 0.009). Overall, enzyme addition decreased FCR, but the effect was greatest with 1% MAF and 82°C or 4% MAF and 85°C. Increasing the MAF and conditioning temperature reduced abdominal fat pad yield (P < 0.03). No difference in breast or leg yield was due to any of the factors (P > 0.05). It is likely that increased MAF improved exogenous enzyme retention and nutrient utilization by broilers. Subject to current fat prices, increasing MAF may reduce the total cost of broiler production, particularly when the reduction of electrical energy usage is considered.