Use of Enzymes to Improve Nutritive Value of Co-Products

UK - The vast majority of feed enzymes used commercially are focussed on improving the availability of nutrients from cereals and soybean meal, the nutrients of interest being one or several of phosphorus, energy, amino acids and other minerals, says Mike Bedford, AB-Vista Feed Ingredients.
calendar icon 2 February 2009
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Speaking at the 42nd University of Nottingham Feed Conference he told an audience that few enzymes have been developed specifically for co-products used in the feed industry, likely as a result of costs for their development and more so their registration.

Nevertheless many of the "main stream" enzymes such as phytases, xylanases and cellulases are used in diets containing co-products since they do target the structural and antinutritive compounds found in such ingredients. They likely do improve the nutritive value of these co-products in many cases, but since there are usually considerably greater quantities of other ingredients which are equally likely to respond to these enzymes, it is difficult to ascribe an accurate value of the enzyme specifically to the co-product.

Wheat milling co-products constitute an example where xylanases enzymes targeting wheat have been used to increase both the nutritive value and inclusion level of this ingredient in both pig and poultry rations. These products consist mostly of the bran and the aleurone layer of cells which remain largely intact after the milling process, thereby effectively "hiding" the nutrients within from the digestive process.

As a result there is potential for cell wall degrading enzymes to expose cell contents to more rapid digestion and hence there is an expectation of potentially large and consistent responses. However, results in practice have been variable and possibly reflect the variation in response of wheat itself to xylanase. Continuing with the wheat co-products example, phytase use has been somewhat successful with the combination of phytase and xylanase giving more consistent responses due to cell walls structurally cloaking phytate from hydrolysis.

Rapeseed meal is an example of an oilseed co-product from the oil industry where the focus has also been on use of enzymes (proteases, phytases and NSP-ases) which were originally developed for the main cereals and soybean meal. Early success in use of NSP-ases and proteases were limited to investigations where the enzyme was used on the raw material prior to diet manufacture (ie in vitro incubations), with successes in feed being more marginal. Phytase has also been successful in upgrading this meal, which has 2 to 3 times the phytate-P content of soybean meal.

However, the phytate in rapeseed meal is less susceptible to hydrolysis than that in soybean meal. The physical location of the phytate may well be responsible for such findings. Since the bio-diesel industry will result in large quantities of this co-product, the need to identify methods of significantly and consistently improving the quality of this co-product becomes more pressing.

Wheat and Maize DDGS have appeared in increasing quantities as a result of the expansion of the bio-ethanol industry. Initial indications suggest there is potential to significantly upgrade these materials although there is uncertainty regarding the consistency of response due to large differences in product composition.

This is driven by differences in production processes between ethanol plants. Once a greater standardisation in process takes place there will be greater success with use of enzymes on these products. For example, if intact cells survive the fermentation process consistently, then there may more repeatable and larger responses than if all cells are broken open.

Methods of determining the value of feed enzymes in diets containing co-products also need consideration. Traditional digestibility studies give some insight but they do not take into account effects of enzymes on portioning of energy between NEgain and NEmaintenance. This is true for NSP-ases and particularly so for phytases. As a result such data should be viewed with caution until performance or NE studies can corroborate digestibility work.

January 2009

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