FEED Business Worldwide - July 2012
Adding wheat to livestock diets with confidence
by Ahmed AMERAH1 and Alexandre PERON2
1 Danisco Animal Nutrition, UK
2 Danisco Animal Nutrition, Singapore
As discussed in last month's animal nutrition article ('Using wheat as an alternative to corn in South East Asia", FBW15 June 2011, Pgs 64 â€“ 66), wheat varies widely in its dietary energy contribution for monogastric animals. This variation is caused predominantly by the level of non-starch polysaccharides (NSP) in the wheat, which have a negative impact on the digestion and absorption of nutrients, and consequently on animal performance.
It is well documented that these negative effects can be overcome by the addition of exogenous glycanases. Therefore, enzyme supplementation of monogastric diets based on wheat is a common practice.
However, to include wheat in diet formulations more effectively, from a cost and nutritional basis, in vitro screening methods that can predict the in vivo response to enzyme supplementation are required. This is important in order to know the 'quality' and feeding value of the wheat to be used in the diet formulation and to include the correct amount of the right enzymes to maximise animal performance and economic returns from the enzyme.
Anti-nutritional factors in wheat
Wheat is affected to a greater or lesser degree by anti-nutritional factors common to many grains, most notably the type and amount of Non-Starch Polysaccharides (NSPs) and the level of phytate contained within them. These in turn are very much associated with the grain variety, crop growing conditions and postharvest storage. Therefore the levels of antinutrients in cereals cannot be assumed to be similar within grain types or between batches harvested in different locations.
Soluble and insoluble NSPs have different properties and consequently different effects on digestion in monogastrics. Two major mechanisms have been proposed to explain the anti-nutritive effects of NSP. The first mechanism is associated with the insoluble NSP fraction, whereby the starch and protein are encapsulated by the fibrous cell wall such that digestive enzymes cannot physically reach them.
The second mechanism relates to the viscous nature of digesta caused by soluble NSP, which can affect nutrient utilisation in a variety of ways. The effects of high intestinal digesta viscosity in poultry are summarised in Table 1. However, pigs appear to be less sensitive to the negative effects of viscosity than poultry because of their more diluted digestive contents. Nonetheless, soluble NSPs have been shown to be an exacerbating factor in the development of non-specific colitis in pigs.
The anti-nutritional effect of phytate is well documented in the literature and, like all other cereal grains, phytate is also present in wheat. However, there is a wide variation of phytate-P level between wheat samples according to cultivar and growing conditions. As evidenced by Selle et al. (2003) the range of phytate P contained in 37 Australian wheat samples varied more than two-fold from 1.35 g/kg to 3.20 g/kg with an average of 2.20 g/kg. The 'phytate effect' in feedstuffs is known to reduce nutrient utilszation, negatively affecting animal performance and also, to be detrimental to the environment. These anti-nutritional effects can be largely overcome by the use of the phytase enzyme in the diet.
The application of endo-1,4-beta-xylanase and phytase enzymes to poultry and swine wheat based diets, is well accepted. Xylanase degrades arabinoxylans in the cell wall, releasing encapsulated starch and other nutrients from inside the cell wall. It also reduces digesta viscosity caused by the soluble arabinoxylans fraction. The net effect is an alleviation of digestive problems, increased nutrient utilisation and consequent improvements in animal performance.
Phytase is another enzyme widely used in either corn or wheat based diets. This enzyme cleaves phosphate groups from phytate, thus increasing phosphorus (P) availability and mitigating the anti-nutritional effect of phytate.
Choosing the right enzyme
Many enzyme products are currently available in the market, raising the question, 'which enzyme to choose and on what basis?' In general, when considering enzymes for animal feed use, characteristics such as specific activity, heat stability during feed processing, activity in the typical pH range of the animal gut and resistance to endogenous proteases should be considered (Selle and Ravindran, 2007). Confidence in the ability of the manufacturer to ensure consistent enzyme quality, with the resources and capability to provide expert support and services are also important criteria in the selection process to reduce risk of variation in product performance.
Can we predict wheat quality and enzyme response?
In short the answer is 'yes', as long as proper time and care is invested in getting the correct information to determine the quality of the wheat that is being used and, subsequently, the correct enzyme inclusion rate. As discussed earlier, the variation in wheat feeding value is mainly caused by the amount and characteristics of NSP present in the grain.
when choosing a feed wheat enzyme.
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