The objective of the current study was to compare the effects of dietary enzymes and nutrient restriction on performance and bone mineralization in birds fed wheat-or sorghum-based diets. A total of 720 d-old male broiler chicks were randomly allocated to 8 treatments, with 6 replicates per treatment and 15 birds per replicate. Birds were reared in floor pens from 0 to 35 d. The study used a 2 x 4 factorial arrangement with 2 grains (sorghum or wheat) and 4 diets: positive control (no enzyme and ME, digestible Lys, Ca, and P sufficient, negative control (NC; no enzyme and reduced ME [-100 kcal/kg], digestible AA [-2%], Ca [-0.12 percentage points], and available P [-0.18 percentage points in the starter phase and -0.22 percentage points in the grower phase]), NC + nonstarch polysaccharide-degrading enzymes + phytase (500 phytase units [FTU]; NCCP), and NC + phytase (1,000 FTU; NCP). From 0 to 35 d, birds fed wheat-based diets had greater G:F (4.5%), BW gain (9.2%), breast meat yield (6.8%), and tibia ash (2.0%) compared with birds fed sorghum-based diets. Across grain types, the NCCP treatment improved BW gain (P < 0.001), feed intake (P < 0.001), G:F (P < 0.05), and livability (P < 0.001) compared with the NC treatment. Birds fed NCP had greater BW gain (P < 0.001), feed intake (P < 0.001), G:F (P < 0.001), and livability (P < 0.001) compared with birds fed NC. Birds fed the NCP diet had greater BW gain (P < 0.001), toe ash (P < 0.01), and tibia ash (P < 0.001) compared with birds fed the NCCP diet. There was a grain x diet interaction for feed intake (P < 0.01), BW gain (P < 0.001), tibia ash (P < 0.01), and tibia breaking strength (P < 0.05). The influence of enzymes was more pronounced in sorghum-based diets than in wheat-based diets. Birds fed wheat-based diets had greater ileal digestibility of His, Met, Val, Phe, Ile, Leu, Trp, Glu, Pro, Ala, Tyr, and Cys compared with those fed sorghum-based diets (P < 0.05). Across grain types, NCP had greater apparent ileal digestibility of Met, Lys, Ser, Pro, Gly, and Cys than NC (P < 0.05). The results suggest that wheat is superior to sorghum for broilers, as expected, but that enzyme supplementation has the capability to restore the compromised bird performance due to feeding sorghum. In addition, compared with nonstarch polysaccharide-degrading enzymes and phytase (500 FTU/kg feed) added in concert, phytase supplemented at 1,000 FTU/kg resulted in a further improvement of some of the performance and bone mineralization parameters in male broilers fed sorghum-based diets.

Reports about the impact of supplemental phytase on metabolisable energy (ME) have been inconsistent. However, ME does not consider partitioning of energy for maintenance, product, or heat increment. Net energy (NE) is a more meaningful measure to evaluate the response of broilers to phytase application in this regard. To date, few data can be found on the effect of microbial phytase on dietary net energy. The current study assessed the impact of three phytase products supplemented at an unconventional high level (all at the inclusion rate of 1000 FTU / kg feed) on net energy of broilers using the indirect calorimetric method (IC). The four treatments were: control, which is a wheat-soybean meal (SBM) based diet with reduced available phosphorus (aP) (2.0 g/kg) and calcium (Ca) (6.0 g/kg); control + intrinsically thermostable 'E. coli' phytase A (phytase A); control + intrinsically thermostable 'E. coli' phytase B (phytase B); control + coated 'E. coli' phytase (phytase C). On d 21, 32 male broilers (Ross 308) were allocated to 16 closed-circuit chambers. The adaptation period was four days and then heat production was calculated by applying the Brouwer equation to measurements of O2 consumption and CO2 production from 25 d to 27 d. ME was determined by the total collection method and NE was calculated as fasting heat production (450 kJ/BW 0.70) + energy gain (Noblet et al., 2010).

The net energy (NE) value may be a better measure than apparent metabolizable energy (ME) of the effect of supplemental phytase on energy utilization in broilers. The present study was conducted to assess the impact of 3 microbial phytases supplemented at an unconventionally high level (1,000 FTU/kg feed) on performance and NE of broilers using the indirect calorimetric method (IC). Four treatments included: 1) Control, formulated to be deficient in ME (12.35 MJ/kg in the starter diet; 12.56 MJ/kg in the grower diet), calcium (0.72% in the starter diet; 0.60% in the grower diet), and available phosphorus (0.25% in the starter diet; 0.20% in the grower diet); 2) control + intrinsically thermostable phytase A; 3) control + intrinsically thermostable phytase B; and 4) control + coated phytase C. A completely randomized design was employed. A total of 384 male broiler chicks were used, and each treatment had 6 replicates with 16 birds per replicate. The birds were reared until d 21 in floor pens with hardwood shavings. Thirty-two birds (8 birds per treatment) were randomly selected to determine heat production and NE (from 25-28 d) following a 3-d acclimatization in the respiratory chambers. Performance results at d 21 showed that supplementation with either of the 3 phytases improved body weight (P < 0.001) and feed intake (P < 0.05), and increased the relative weights of tibia ash (P < 0.05) and toe ash (P < 0.01). Phytases A and B increased the NE value of the diet (P < 0.05). It may be concluded that the negative effects imposed by calcium and available phosphorus down-specification can be compensated by phytase supplementation in general, and intrinsically thermostable phytases improve the ME and NE value. However, phytase did not reduce heat production, heat increment, or increase NE:ME in birds.

Although the main non-starch polysaccharides (NSPs) in wheat are arabinoxylans, considerable amounts of β-glucan and cellulose are also present. In soybean meal (SBM) and canola meal, the major polysaccharides are pectins and cellulose. Since more plant ingredients containing different forms of NSPs are being used for diet formulations, an enzyme combination with additional activities each differing in substrate preference may further enhance nutrient utilization. A study was conducted to investigate the use of Rovabio Excel LC (liquid), an enzyme complex containing 19 carbohydrase activities on broilers fed a nutritionally adequate or downspec diet.

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.

This thesis presents a literature review and reports on four experiments conducted to investigate the effect of multi-carbohydrase with or without phytase on the growth performance in broiler chickens. To scrutinise the mechanisms underlying these effects, a series of responses in relation to the digestibility of nutrients, energy utilisation, especially net energy of the diet, bone mineralization and gut microflora were examined.