Effect of Soybean Meal Varieties, Phytase Enzyme, and Particle Size of Corn on the Performance of Broilers

Phosphorus (P) has been considered to be one of the most expensive feed ingredients in poultry production. Excess fecal excretion of P has also created environmental concerns since it has been shown to contribute to eutrophication of water bodies. Several strategies have been proposed and can be adopted to reduce the excretion of P and reduce incorporation into diets. The use of feed ingredients such as low phytate P (LP) grains (e.g. corn, canola) and legumes (e.g. LP SBM) that have been genetically selected to contain more available P and less phytate P have been proposed. The use of exogenous feed enzymes such as phytase that liberate P from phytate molecule (an anti-nutritional factor in feed) has become successful in poultry production. Last, modification of gastrointestinal tract functions through feed particle size manipulation provided a promising means to improve digestibility of available nutrients in feed. Therefore, in this series of experiments, these three strategies were investigated with broilers. In the first experiment, chicks were raised to 21 d in battery cages to study the effect of feeding coarse corn (CC) and SBM varieties (LP and normal phytate (NP)) from 9-21 d. Results showed that 50%CC produced a larger gizzard and smaller proventriculus while phytate P digestibility was improved by either feeding 50%CC or NP SBM. In the second experiment, 300 FTU/kg of phytase was investigated in addition to CC and SBM varieties. Chicks were again raised to 21 d of age in battery cages. Results showed that feeding either 50%CC or LP SBM improved P digestibility, and increased gizzard weight at 21 d. Adding 300 FTU/kg improved total P digestibility in the presence of 0%CC but 50%CC. Furthermore, adding 300 FTU/kg to the LP SBM diet improved total P digestibility compared to the NP SBM diet. In the third experiment, the same experimental dietary combinations were used with male chicks raised in floor pens to 35 d. The AdjFCR was improved by phytase addition to the NP diet but was poorer with the LP diet from 23 to 35 d. The improvement of total P digestibility was better when phytase was used in combination with LP SBM than with NP SBM. On the other hand, adding phytase to either 0%CC or 50%CC improved total P digestibility. In the fourth experiment, a combination of SBM varieties with phytase enzyme either added "on top" of diet or incorporated with a matrix value, or without phytase were investigated. Female chicks were raised in battery cages to 35 d and treatments started after 21 d. Feeding LP-LS SBM produced a smaller gizzard and increased BW gain from 22-35 d as compared to NP diets. Feeding 300 FTU/kg of phytase added "on top" of diet or with matrix value improved total P digestibility compared with the non phytase control treatment.