A study was conducted to examine the effects of a multi-carbohydrase enzyme complex on the nutritive value of wheat in diets differing in nutrient density. It was hypothesised that response to enzyme inclusion would be greater in diets with lower nutrient density. The study was conducted using 1008 Ross 308 male broiler chicks (four treatments with seven replicate pens of 36 chicks). A 2 × 2 factorial arrangement of treatments was employed. Factors were adequate or low nutrient density with or without enzyme supplementation. The wheat-soybean meal based positive control (PC) diet was formulated to be nutritionally adequate in energy and digestible amino acids according to local industry recommendations. A negative control (NC) was formulated to have 80 kcal/kg less ME and 1.5% less digestible amino acids as compared to the PC. A multi-carbohydrase complex containing 19 carbohydrase activities derived from Penicillium funiculosum was added in both the PC and NC diets (Rovabio® Excel LC, Adisseo Asia Pacific Pte Ltd., Singapore). Birds fed the NC had 3.7 points (P < 0.05) poorer FCR than the PC. Across the diet type, enzyme supplementation increased body weight by 3.2% (P < 0.05) and improved FCR by 5.2 points (P < 0.01). There was no nutrient density x enzyme interaction (P > 0.05), indicating that performance improvement was independent of nutrient density. Apparent ileal digestibility of crude protein followed a similar trend, showing a 4.9% enhancement (P < 0.01) with the inclusion of the enzyme product in either diet. Enzyme supplementation reduced ileal viscosity by 39.0% (P < 0.05). It was concluded that multi-carbohydrase could overcome the negative effect in broiler performance brought by nutrient reduction, however, there was no indication that nutrient density affected bird response to supplementation of multi-carbohydrase.

Published literature on the effect of carbohydrase enzymes (CE) on energy availability, nutrient digestibilities and growth performance of broilers fed corn-soybean meal-based diets is reviewed. Data from experiments involving CE preparations displaying single- to multiple-activities has shown improved metabolisable energy by 3% and digestibility of protein by 5%. Despite the observed variation in absolute values for individual amino acids, the improvement in amino acid digestibility appeared to be 27% of the undigested fraction. The positive effect on nutritive value are consistent with the improvements in body weight gain (0.8 to 10.4%; mean = 4.3%) and feed efficiency (1.3 to 9.3%; mean = 3.7%). Possible mechanisms contributing to these effects and the factors thought to explain the variability in responses has been discussed.

As the simultaneous use of carbohydrases and phytases gains momentum it is imperative that formulators understand the magnitude of additivity of effect to allow for appropriate modification to diet nutrient balance. Though carbohydrases and phytases are often thought of as pronutrients with energy, calcium and phosphorus value, within the scientific literature there are dozens of papers on the effect of these enzymes on ileal amino acid digestibility coefficients. The effect of enzymes on ileal amino acid digestibility is instructive as patterns of response allow speculation as to mode of action and likely additivity of admixtures. A review of the scientific literature has revealed that whilst xylanases and phytases may be considered to be broadly additive in effect, on an individual amino acid basis this effect ranges from sub-additive (e.g. threonine) to synergistic (e.g. arginine). Importantly, the mean response to both xylanase and phytase for ileal amino acid digestibility can be predicted (R2=0.65 and 0.56 respectively) by polynomial equations based only on the nutritional value of the control diet. The fact that control diets with an inherently high digestibility respond poorly to enzymes explains why the use of a second enzyme will likely yield a lesser response when used on top of another, since the former has already improved digestibility characteristics. The implications of these responses, as well as suggested mechanisms of action, are discussed within practical diet formulation constraints.

Energy utilization in broilers as influenced by supplementation of enzymes containing phytase or carbohydrase activities was investigated. Day-old male broilers (480) were allocated to four slaughter groups, thirty broilers in the initial slaughter group and 150 broilers in each of the final slaughter groups on days 7, 14 and 21. Broilers in each of the final slaughter groups were allocated to five treatments in a randomized complete block design, each treatment had six replicate cages of five broilers per replicate cage. The diets were maize–soyabean based with wheat as a source of NSP. The treatments were: (1) positive control that met nutrient requirements of the day-old broiler chick; (2) negative control (NC) deficient in metabolizable energy and P; (3) NC plus phytase added at 1000 FTU/kg; (4) NC plus cocktail of xylanase, amylase and protease (XAP); and (5) NC plus phytase and XAP. Gain and gain:food were depressed (P < 0·05) in the NC diet. Phytase improved (P < 0·05) gain at all ages and gain:food at days 0–14 and days 0–21. There was improvement (P < 0·01) in net energy for production, energy retained as fat and protein from days 0 to 14 and from days 0 to 21 in phytase-supplemented diet compared with the NC diet. Net energy for production was more highly correlated with performance criteria than metabolizable energy and may be a more sensitive energy utilization response criterion to use in evaluating broiler response to enzyme supplementation.