3rd International Poultry Meat Congress

10000 u/kg), diet 4 contained another bacterial protease (protease 2; 10000 u/kg) whereas diets
5, 6 and 7 contained admixture of xylanase from T. reesei, amylase from B. licheniformis, and
protease from B. subtilis (Axtra XAP; Danisco Animal Nutrition, DuPont Industrial Biosciences)
at graded levels (50%, 100% and 200% the recommended dose for broilers, containing 2500,
5000, or 10000 protease u/kg). The diets were fed for 7 days, excreta samples were collected
for the last 3 days of the experiment and ileal digesta samples were collected on the last day of
the study.
The total tract flows of arabinose, xylose, galactose, glucose, and glucuronic acid from the
NSP fraction (Figure 4) were reduced at the higher doses of protease, and both the intermediate
and the high dose of xylanase/amylase/protease. In the specific case of xylose and arabinose,
which are the main sugar components of arabinoxylans, the inclusion of xylanase and amylase
generally reduced the flow of these sugars compared to protease alone at a comparable dose.
These data suggest that fibre degradation may be one of the mechanisms by which proteases
increase the digestion of nutrients in chickens. Although the reason of these effects of protease
on NSP digestion is not known, studies in ruminant models have suggested that the use of
proteases can disrupt cell wall associated proteins, which facilitates microbial colonisation of
the substrate (Colombatto and Beauchemin, 2009). However, effects of exogenous proteases on
the gut microbial populations of chickens have not been properly studied.
Figure 4. Total tract flow of total sugars from the non-starch polysaccharides (NSP) fraction
in 21-d-old broilers fed corn/soybean meal diets supplemented with different doses of two
bacterial proteases or a combination xylanase, amylase, and protease (XAP).
Other Factors Affecting The Bio-Efficacy of Proteases
Effects of feed proteases that are not directly related to nutrient digestibility have also been
reported in the literature. For instance, Caine et al. (1998) reported a reduction in the level of
trypsin inhibitors of soybean meal with the use of a serine protease, which may be present in
practice and has not been fully recognised as one of the effects of value for poultry diets. Positive
effects of exogenous proteases on the ability of birds to cope with intestinal disease challenges
like Eimeria infections or necrotic enteritis have also been suggested, although mechanisms are
not well understood and the evidence available is not definitive. Peek et al. (2009) found that a
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