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Livestock Production
Wednesday, July 25, 2007 4:50:38 PM
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Effects of phytase and xylanase addition to corn and wheat-based diets on broiler performance

M.B. Lu, D.F. Li, L.M. Gong and Y.J. Ru



An experiment was conducted to evaluate the effect on broiler performance of adding phytase and xylanase, alone or in combination, to diets based on corn, wheat, soymeal and rapeseed meal.


All experimental diets, including a normal phosphorus commercial diet (NP,4.5 g AvP/kg for day 0 to 21 and 4.0 g AvP/kg for day 22 to 35), low phosphorus diet (LP, Reduced AvP of NP by 1.5 g/kg for both starter and finisher diets), LP diet with phytase (LP+P), xylanase (LP+X) and their combination (LP+P+X) respectively, were offered to broilers as mash from day 1 to 35. Feed intake and body weight gain were measured weekly.


Growth rate and feed efficiency were depressed in birds given the LP diet, but performance was improved to the level of birds given the NP commercial diet when the LP diet was supplemented with 500 FTU/kg phytase. Addition of xylanase to the LP diet had no effect on performance (P>0.05). Supplementation of xylanase to the LP+P diet, however, tended to produce an improved feed conversion compared with the LP diet supplemented with phytase alone.


It has been generally recognised for some time that arabinoxylan is a key anti-nutritional factor in poultry diets compounded from wheat and its by-products.


Arabinoxylan has a high water holding capacity, which can increase the viscosity of digesta and reduce nutrient digestibility, consequently depressing growth performance.


Annison (1993) reported that wheat contains 6.2 to 7.0 percent and corn contains 4.1 to 4.5 percent arabinoxylan.


Due to the lack of endogenous fibre-digesting enzymes in poultry, digestion of dietary fibre mainly occurs in the hindgut through bacterial fermentation, with the digestibility of arabinoxylan being related to the maturity of birds.


More importantly, the existence of arabinoxylan in the diet can restrict other nutrients being digested and absorbed by birds, resulting in depressed growth performance. Addition of exogenous enzymes to wheat and corn-based diets increases digestibility of nutrients in broilers (Pen et al. 2003). It may also provide additional dietary energy as well as short chain fatty acids and oligosaccharides (Iji 1999).


Phytate is another anti-nutritional factor commonly found in many plant-based ingredients in poultry diets, and which can substantially reduce phosphorus availability.


Typically, only about 30 percent of dietary phosphorus can be utilised by birds with the rest being excreted into the environment. Apart from the effect of phytate on phosphorus availability, phytate also has the capability to bind with protein, reducing the availability of amino acids. Many published research studies have shown that addition of exogenous phytase not only improves bioavailability of phytate phosphorus, but also improves digestibility of energy and amino acids (Ravindran et al, 1999).


The study concluded that including 500 FTU/kg phytase (Danisco's Phyzyme XP) to a diet with low available phosphorus (3.0 g/kg) significantly improved daily gain, feed intake and feed utilisation efficiency of broilers during the 35-day growth period.


Adding xylanase alone to the low phosphorus diet did not improve bird performance, probably because phosphorus availability was the first limiting factor in the diet, and the potential effects of xylanase on energy utilisation and amino acid digestion were not reflected in growth performance.


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Article made possible through the contribution of Australian Poultry Science Symposium.

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