Assessing apparent, true and standardized ileal amino acid digestibility of cottonseed meal-containing diets with or without a microbial enzyme blend

With approximately 30.2-56% crude protein (CP), cottonseed meal (CSM) is regarded as one of the closest alternative protein sources to soybean meal (SBM). It is used at relatively low levels to replace soybean meal in diets for broiler chickens (Swiatkiewicz et al., 2016). While its value at such low levels has been well established, the potential for using CSM at higher levels when fed as such or supplemented with microbial enzymes is not well understood. Similarly, there have been relatively few studies on the digestibility of amino acids in CSM-containing diets, particularly when supplemented with microbial enzymes (Nagalakshmi et al, 2007). The objective of this study was to examine the effect of a new-generation composite enzyme product (xylanase/β-glucanase activities) on apparent (AID), true (TID) and standardized ileal amino acid digestibility (SID) in diets containing moderately high levels of CSM, fed to broiler chickens from hatch to 35d. Four isocaloric and isonitrogenous basal diets were formulated from wheat/sorghum/soybean meal. Cottonseed meal was included at 0, 4, 5 or 6 % in the starter diets; at 0, 8, 10 or 12 % in the grower diets, and at 0, 12, 15 or 18 % in the finisher diets, with or without supplementation with 100 mg per kg diet of xylanase and β-glucanase blend (Danisco Animal Nutrition, Marlborough, UK). The ninth diet was a nitrogen-free reference diet (NFD), which was fed to birds from d19 to d24. Each treatment was randomly assigned to 6 replicates (10 birds each).

Apparent ileal digestibility of arginine increased linearly (P < 0.013) with increasing level of CSM. The AID of histidine, leucine, lysine, alanine, glycine and tyrosine was also improved (P < 0.05) by enzyme supplementation. There was a significant interaction (P < 0.05) between CSM level and enzyme on the TID of all measured dietary amino acids arginine, methionine, serine and tyrosine except (P > 0.05). Cottonseed meal decreased (P < 0.05) the TID of almost all amino acids, except for arginine, phenylalanine, valine, glutamic acid and proline. Enzyme incorporation more than offset (P < 0.01) the reduction in TID of amino acids caused by CSM inclusion. An interaction (P < 0.01) was observed between CSM and enzyme on SID of methionine. Increasing the CSM inclusion level significantly decreased SID of histidine, lysine, methionine, alanine, glycine, serine, and tyrosine. Supplementing CSM diets with the enzyme product increased (P < 0.05) the SID of all the indispensable AA and most of the dispensable AA but had no effect (P > 0.05) on SID of histidine and phenylalanine.

The results showed that supplementing CSM-containing diets with the test microbial enzymes improved the ileal AA digestibility, enabling a higher inclusion of CSM in diets for broiler chickens.