Impact of feeding constant levels of cottonseed meal with enzymes on broiler meat yield, visceral organ development, endogenous enzyme activity and nutrient digestibility

Cottonseed meal (CSM) is a by-product of oil extraction from cotton seeds and is a moderately rich source of protein (30.2-56 %). A recent review concluded that CSM is an acceptable ingredient in poultry diets (Świątkiewicz et al., 2016). However, the use of CSM as a protein source in poultry diets is limited due to the presence of gossypol, variation in nutrient composition and a relatively low lysine level compared to soybean meal, all of which have negative effects on the growth performance of broiler chickens (Nagalakshmi et al., 2007). Enzyme supplementation to improve the nutritive value of feedstuffs for poultry is a regular practice. However, there is scant literature on the use of microbial enzymes to improve the nutritive value and utilization of CSM in poultry feed. A new-generation microbial composite product of xylanase and beta-glucanase (Danisco Animal Nutrition, Marlborough, UK), was examined in the current study, with the aim of increasing CSM levels in broiler chicken diets.

Visceral organ development, meat yield, digestive enzyme activities and nutrient digestibility were assessed in broiler chickens offered diets containing constant levels of CSM throughout the production cycle (d1-d35) and supplemented with microbial enzymes. Nine isocaloric and isonitrogenous diets were basically formulated from wheat/sorghum/soybean meal. Three levels of cottonseed meal (0 without, 6 % in starter, grower and finisher or 12 % in all three growth periods) were supplemented with three levels of xylanase and β-glucanase blend (Axtra XB) at 0, 250 or 500 g/tonne of diet, targeting the arabinoxylans and β-glucans found in grains and CSM. At d10, results showed that the weight of the small intestine and the combined weight of gizzard and proventriculus were increased (P < 0.01) due to inclusion of CSM in the diet. The relative weights of thighs and drumsticks increased linearly (P < 0.05) with increasing CSM level in the diet. There was an interaction (P < 0.05) between CSM and microbial enzyme on starch digestibility. Addition of the enzyme blend improved (P < 0.05) protein and energy digestibilities, with better results observed when 250 mg/kg was added. A slight reduction (P < 0.05) in dry matter digestibility was observed in the groups raised on CSM-containing diets. Adding microbial enzyme blend up to 250 mg/kg diet increased (P < 0.05) the activities of maltase, sucrase, aminopeptidase, chymotrypsin and lipase at d10, while at d24, sucrase, alkaline phosphatase, aminopeptidase, trypsin and chymotrypsin activities were also improved (P < 0.05) . On the other hand, feeding a high level of CSM (12 %) 1-10 days post-hatch negatively affected (P < 0.05) the activities of aminopeptidase, trypsin and chymotrypsin.

The results demonstrate that feeding CSM to broiler chickens did not adversely affect meat yield and nutrient digestibility. Furthermore, adding xylanase and beta-glucanase blend to CSM-containing diets enhanced the activities of endogenous enzymes and digestibility of nutrients. The current study found that a high level of CSM may not be suitable for young birds.