A novel approach to feed enzyme use - combining xylanase with high doses of phytase in poultry diets
The economic benefits of using a high quality xylanase to improve nutrient digestion in poultry diets are well proven, as are the financial gains possible from phosphorus release using a standard dose of phytase. The widespread use of phytase within the poultry sector -- market penetration exceeds 80% -- means that the vast majority of xylanase use is now in diets also containing a phytase.
However, the growing popularity of phytase superdosing to eliminate the anti-nutritive effect of phytate raises the question of whether xylanase addition can still provide worthwhile returns alongside a substantially higher than standard dose of phytase. The key lies in the considerably different mode of action of the two classes of enzyme, and whilst the benefits are not strictly additive, the latest research confirms sufficient additional gains to provide a net positive return on investment.
The vast majority of the research investigating feed enzyme use, whether xylanase, phytase at standard dose rates or phytase superdosing, has been carried out using only a single enzyme. In recent years, however, a substantial body of data has begun to emerge from xylanase trials using diets also containing a standard dose of phytase.
Such results are arguably the most relevant to what could currently be considered standard practice within the poultry sector, and have provided an early indication of the potential advantages of combining these two classes of enzymes. The varied success of such trials has also highlighted the wide disparity in efficacy that comes with differing enzyme characteristics, even within the same enzyme class.
The use of enzymes with characteristics specifically targeted to maximise efficacy in the animal is therefore critical, whether evaluating a single enzyme, or several. It is also important to clearly differentiate between the results obtained by combining enzymes of different classes – in this case a non-starch polysaccharide (NSP)-degrading enzyme with a phytase – from the use of enzyme products with multiple activities within the same class, such as combining a xylanase and a glucanase (both NSP enzymes).
Modes of action
The evidence for the benefits of the latter remain subject to considerable debate, with the data produced to date failing to show any clear advantage of such multi-NSP-enzyme dosing (i.e. multiple activities within the same enzyme class) over a well-targeted single-enzyme xylanase product. Potential conflicts between similar modes of action, such as breakdown of the beneficial end products of xylanase action, as well as difficulties achieving equal levels of thermostability and efficacy in the bird, appear the most likely reasons.
This is not the case when combining enzymes from different classes with very different modes of action, where there appear to be clear advantages to be gained. Xylanases have been shown to be highly effective in improving performance in viscous (wheat- and barley-based) and non-viscous (corn- and sorghum-based) diets, with or without the presence of a standard dose of phytase.
At the most basic level, xylanases act both by eliminating the nutrient encapsulating effect of the plant cell wall, and by breaking down the long-chain, soluble NSPs (particularly arabinoxylans and mixed-linked β-glucans) to reduce digesta viscosity. Each not only effectively improves access to feed materials for the bird's digestive enzymes, but can also increase access to the high levels of phytate present in the fibre fraction of plant feed ingredients.
Where a standard dose of phytase is used to release phosphorous by breaking down plant phytate, and so allow a reduction in the added inorganic phosphorous in poultry diets, there appears to be little, if any, conflict between this mode of action and that for a xylanase. In fact, any failure to produce additional gains in this situation is most likely due to one or both enzymes being sub-optimal in terms of the characteristics needed for maximum efficacy.
When the target is to achieve as near complete phytate elimination as possible through phytase superdosing, the action of xylanase in improving phytate availability would appear to offer even greater benefits. Providing the phytase used is optimised for superdosing – intrinsically thermostable without the need for coatings, high levels of activity in the stomach, able to degrade even low concentrations of phytate – the result should be an additional gain beyond the typical three to four point improvement in broiler feed conversion efficiency seen with phytase superdosing alone.
Figure 1 - The additive effects of xylanase plus phytase on weight gain in 0 to 35-day-old broilers (Source: Kühn et al., 2013)
As would be expected, the standard 500 FTU/kg phytase dose returned performance of the negative control to that of the positive control, whilst superdosing with 1500 FTU/kg of the phytase alone produced a significant improvement in bodyweight gain. Most importantly, the addition of a standard 16,000 FXU/kg dose of the xylanase produced a further gain in performance that is both statistically significant and economically beneficial, whether used to boost performance or add to the matrix and further reduce feed costs.
It must be remembered, however, that not all phytases are equally effective for phytate elimination through superdosing and not all xylanases are equally effective in degrading dietary NSPs. This creates a challenge for the end user who is faced with a myriad of commercial enzymes and often conflicting supplier claims, with independent trial results remaining the only truly reliable reference when it comes to product choice.
The move towards higher doses of phytase to remove the anti-nutrient effects of phytase offers an opportunity for poultry producers to gain an even greater return from investment made in feed enzymes. If that return can be enhanced yet again by combining a well-proven superdosing phytase with an effective xylanase known to provide additional gains in such situations, then this strategy could become the new standard practice for poultry producers worldwide.
Article made possible through the contribution of Dr. Carrie Walk, Gilson Gomes and AB Vista