The use of protease in animal feed focuses generally on cost reduction. However, by maximising the digestibility of protein sources, animal producers can reduce crude protein concentration and use lower cost protein sources without affecting animal health and performance.
Corn and soybean meal (SBM) have shown a positive, predictable pattern response to the inclusion of exogenous enzymes and amino acid digestibility is reliably elevated. However, some ingredients such as canola meal (CM) respond differently, suggesting that anti-nutrients and/or inhibiting factors have an important role in the interference of protease effectiveness.
Variance in enzyme effect under experimental conditions depends on a number of factors, including the inherent digestibility of nutrients, species, age as well as environmental and nutritional factors. Although the exact reasons why the effect of proteases vary with different feed compositions requires further research, it seems reasonable to conclude that the effect of proteases on animal health is not limited to digestibility.
Soybean meals, for instance, contain a range of specific anti-nutritional factors that may not be completely inactivated by oil extraction and thermal conditioning. Ghazi et al. (2002) noted that the addition of mono-component proteases significantly reduced the anti-SBM-specific immunoglobulin G in serum of broiler chicks fed a corn/soy-based diet, suggesting that exogenous proteases have the capacity to degrade antigenic proteins in soybean meal and/or to degrade proteinaceous antinutrients such as trypsin inhibitors and lectins, which can irritate the gut mucosa, and activate the immune system. These results suggest a potential role for proteases in gut health that deserves further investigation.
Nutrient recovery: Rooke et al. (1998) observed that proteases have the capacity to preferentially degrade a type of antigenic protein contained in SBM (β-conglycin) that can cause a hypersensitive immune response. Due to the strong link between immune response and diet, it’s possible that the suppression of these effects through the degrading effect of exogenous protease would have direct benefits to nutrient recovery, and therefore digestibility and absorption.
Mucin production: Cowieson and Roos (2014) noted that there was a significant correlation between the pattern of response in amino acid digestibility improvements with an exogenous protease and the amino acid profile of intestinal mucin. This correlation suggest that some of the benefit in apparent amino acid digestibility associated with protease use in pigs and poultry is related to a reduction in mucin loss from the ileum.
Under the supervision of Professor Adeola, a team at Purdue University investigated other potential mechanisms of action of proteases using a gene expression method. There are several consequences for the appropriate deployment of exogenous proteases which may explain the differences in effect in the two control diets in the study analysed here.
Broiler chickens were tested in a 21-day cage study to evaluate the interactive effects of dietary protein and an exogenous protease (Ronozyme ProAct), see Table 1. For the first week, birds were fed a common starter diet and four corn-based dietary treatments were arranged with two major sources of protein, soybean meal (SBM) and canola meal (CM) with or without exogenous protease. Feed gain was enhanced by 9% in SBM-free diet but almost 14% in SBM diets. Protease was more effective in enhancing performance in SBM-based diets and ileal nitrogen digestibility was increased in both diets. This improvement in ileal digestibility with protease in the SBM-based diet (~80 kcal/kg) must therefore be associated with effects beyond protein digestibility.
The expression of Interleukin-8 (IL-8), associated with inflammation, is elevated on day 14 in the jejunum. This may be due to an innate immune response to antigenic soy protein. In contrast to IL-8, IL-10 is an anti-inflammatory cytokine and higher levels are usually associated with reduced inflammation. In the present experiment, application of an exogenous protease reduced the expression of IL-10 suggesting a reduction in the production of anti-inflammatory cytokines in the jejunum. This
suggests that proteases may be able to reduce diet-derived inflammation.
On day 21, the expression of Claudin1, a gene that is associated with tight junction integrity (and therefore good gut health), was upregulated in birds that received the diet based on CM and also by exogenous protease inclusion. This result suggests that intestinal integrity, or at least the integrity of the tight junctions in the jejunum, are promoted by CM inclusion and also by application of exogenous protease.
It is possible that these effects are mediated indirectly via changes in microbial fermentation of protein and a proximal shift in the site of protein recovery or directly via enhanced Lys and Pro availability for collagen synthesis. The addition of exogenous proteases also resulted in a significant reduction of the expression of the gene jejunal MUC-2, associated with intestinal mucin production. Jejunal MUC-2 were observed on day 14, the addition of exogenous protease resulted in a significant reduction of the expression of jejunal MUC-2, which is associated with a reduction in intestinal mucin production, usually associated with energy loss. Mucin is naturally produced as part of the digestion process but can also be associated with energy loss. Exogenous proteases have shown potential to support the digestive process reducing mucin production, therefore limiting the amount of energy used for digestion.
In conclusion, exogenous protease is effective in enhancing the performance of broiler-fed diets based on corn and soybean meal. And the results of this study suggest that exogenous protease benefits diets that contain a substantial concentration of SBM due to a reduction in the allergenicity of antigenic proteins, reducing intestinal inflammation. The present work also confirms the potential influence of exogenous protease on digestive dynamics through altered secretion of intestinal mucin, improved tight junction integrity and changed emphasis on amino acid transport.
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