Where the rest of the world relies on maize or wheat as a source of carbohydrates in poultry feeds, down under in Australia also a lot of sorghum is used. This grain, which can proliferate under dry conditions, requires a different approach in the feed mix and also enzymes that work in maize and corn react different in sorghum based feeds.
Distillers’ dried grains with solubles (DDGS) are becoming increasingly important in poultry feeding. Research into the use of this material has focused largely on maize DDGS from North America and less work has been done on the predominantly sorghum DDGS that are produced in Australia. Barekatain, Iji and Choct at the University of New England in New South Wales conducted a feeding trial with sorghum DDGS and a xylanase enzyme (Ronozyme WX, DSM) in broiler chickens. They found that feed intake was significantly increased with the inclusion of dietary DDGS in the diet compared to the control diets. There was no effect on body weight gain from the addition of DDGS or xylanase. Feed conversion ratio (FCR) deteriorated significantly with the rising level of DDGS in diets during the first three weeks of feeding. Over that period, the effect of xylanase supplementation was not significant at up to 20% DDGS inclusion. However, in birds fed 30% DDGS, the FCR was significantly improved by the addition of xylanase, over the starter and the entire feeding period of the study, with birds ending up with similar body weight but tending to consume less feed as a result of xylanase addition. From this trial they concluded that xylanase may help to limit the detrimental effect of high DDGS inclusion especially in the starter phase of feeding.
Enzyme effect on sorghum digestibility
Broilers offered sorghum-based diets often have sub-optimal performance when compared to birds fed wheat-based diets. The cause of poor performance appears to relate to reduced energy availability. A study of Sultan and co-workers at the University of Queensland was carried out to determine if dietary enzymes improve protein and starch utilisation of sorghum by 21-day-old broilers. They added various enzymes to the basal diet that was fed as a mash feed. The results showed that the ileal protein and starch digestibility coefficients were improved with the addition of dietary enzymes, especially phytase and protease combinations. Interestingly, xylanase combined with phytase resulted in the greatest numerical improvement in both starch and protein digestion. The combination of all three enzymes improved the protein (8.3%) and starch (16.0%) coefficients, substantially, when compared with the control diet. A strong positive correlation between protein and starch digestibility coefficients was observed. It was concluded that application of dietary enzymes to sorghum based broiler starter diets has the potential to increase protein and starch digestion and hence energy availability.
Good old phytase
Phytase is the most widely used and researched enzyme globally and has been around for many years. Several generations of phytase with higher effectiveness have been brought to market and still its limits have not been reached yet. A lot has to do with the great variability in phosphorus and phytate content of plants grown under different conditions. Olnood, Liu and Gady of Adisseo Asia Pacific collected more than 200 samples worldwide (mainly cereals, cereal by-products, oilseeds and oilseed meals) and analysed these for concentrations of total phosphorus (P) and phytate P. Results (Table 1) showed that phytate P content varied from 18% in cassava to 83% in rice bran of the total P content. There were large variations within crop species in terms of phytate P/total P ratio which ranged from 64-87% in maize (corn), 64-80% in wheat, 66-95% in rapeseed meal and 59-69% in soybean meal.
These huge variations make it rather difficult to determine what enzyme to use and in what dosage. Not all enzymes work in specific combinations as was found by Hughes and co-authors in Australia. In two experiments they evaluated the apparent metabolisable energy (AME) values for high screenings and other weather damaged samples of cereal grains (wheat, barley, triticale and sorghum) and commercial companies’ donated cereals. The grains were fed to broiler chickens.
All grains were fed with and without a blend of xylanase being Porzyme 93010 (Danisco) at 50 g/tonne for wheat, barley and triticale, or Rovabio Excel (Adisseo) at 200 g/tonne for sorghum and a phytase (Phyzyme TPT, Dansico) at 50 g/tonne.
In Experiment 1, there were significant 2-way interactions between grain type and enzyme and grain type and sex on AME values for high screenings grains (Table 2).Regression analysis indicated AME values for grain declined by about 0.2 MJ/kg for each 10% rise in screenings, in both male and female chickens, when given enzymes. In the absence of enzyme, the responses to screenings were highly variable, particularly for male chickens. When using better quality cereals the researchers found a significant 3-way interaction between individual grains, enzyme and sex. Enzymes improved AME for only one sample of barley fed to male chickens.
The results of both experiments showed that the blend of xylanase and phytase enzymes improved AME values for some, but not all wheats, and only one sample of barley. Other types of grain were unaffected. Variable responses of different wheats to enzymes were observed in high screenings grains with presumably higher than usual concentrations of soluble and insoluble NSP. Increasing concentrations of insoluble NSP, but not soluble NSP, depressed AME values for wheat sourced from commercial feed mills.
Phytase not only affects P
It is becoming clear that microbial phytase not only increases the availability of phytate-bound P, but also has an effect on several other important minerals, protein, and amino acids in poultry diets. However, literature on this effect is limited, which was the reason for Zaefarian and Ravindran of Massey University in New Zealand in cooperation with Dansico to conduct a study to determine the effects of phytase supplementation in phosphorus-adequate maize- and wheat-based diets on the performance and nutrient digestibility of young broilers.
In both diet types, supplemental phytase improved the weight gain and feed conversion ratio, and increased the apparent ileal digestibility of nitrogen, lipids and phosphorus. Improvements in the apparent ileal digestibility of palmitic, stearic, oleic and linoleic acids were also observed. Phytase supplementation had no effect on the nitrogen-corrected apparent metabolisable energy in both diet types, but tended to improve the ileal digestible energy in wheat-based diets. They also concluded that overall phytate is an anti-nutritive factor that can impair the availability not only of phosphorus and protein but also of lipid and fatty acids, resulting in the depression of growth and feed conversion efficiency of young broilers fed phosphorus-adequate maize- and wheat-based diets. These adverse effects can be overcome by supplemental phytase.
Non-starch polysaccharides (NSP) are found in almost all ingredients of vegetable origin. These NSP are polymeric carbohydrates with different composition and structure from starch and considered anti-nutritional factors with poor digestibility in poultry. Soybean meal contains a significant quantity of NSP (210-220 g/kg dry matter), including 55% of pectins which poultry cannot digest. The NSP-degrading enzymes target the cell walls of vegetable ingredients, not only for cereals such as corn, wheat or barley, but also for soybean meal and other vegetable protein meals, especially the insoluble components resulting in an easier access of digestive enzymes. Numerous studies have demonstrated that the negative effects of NSP can be overcome by supplementation with suitable exogenous enzyme preparations. At Adisseo two field studies were conducted to investigate the responses of a combined NSP-degrading enzyme and phytase (multi-enzyme Rovabio Max) in laying hens fed on corn-soybean meal based diets (positive control, PC) and a group (negative control, NC) with reformulated diets in which dicalcium phosphate (7.5 and 8.9 kg/t) was entirely replaced. The results showed that hens fed on the NC diets performed significantly worse, with lower feed intake and laying rate and increased mortality, whereas the enzyme treatment fully restored these parameters to the levels of the PC diets. The results suggest an intake of available P at 160 mg/hen/day is insufficient and the combined enzymes contribute ME 0.18-0.21 MJ/kg and available P 1.2-1.5 g/kg.
NSPs from viscous grains such as wheat and barley are mainly composed of arabinoxylans and -glucans, polymers which are known for their anti-nutritive effects in poultry. High levels of soluble NSPs result in increased gut viscosity. High levels of insoluble NSPs result in increased water-holding capacity, reduced access for digestive enzymes (nutrient packaging) and increased endogenous secretions. Ultimately, these effects lead to reduced performance and nutrient utilisation. They can also result in increased microbial proliferation in the gut and poor litter quality.
Xylanase and -glucanase can overcome these problems, which are known from many studies. However, due to characteristics such as affinity for substrate, pH range of activity or susceptibility to cereal endogenous inhibitors, the bio-efficacy of glucanases (carbohydrate degrading enzymes) can vary widely. Danisco and the University of Queensland investigated the efficacy of a new product containing both xylanase and -glucanase activities in broilers fed wheat/barley-based diets.
Results showed that xylanase and -glucanase supplementation improved bird performance during both starter and grower-finisher periods, increasing weight gain from 2.9 to 4.5% and decreasing FCR from 2.9 to 4.2% depending on inclusion rate. Mortality was not affected. In the conditions of this trial, the lowest dose (0.05 kg/tonne) of the new enzyme gave the highest biological response in the bird. These benefits will be related to the breakdown of both soluble and insoluble fibre fractions from wheat and barley grains.