Energy is an expensive ingredient in today's pig diets. The downside of cheaper feed energy sources is often a reduced availability of nutrients, resulting in a trade-off between cost of diet and animal performance. Carbohydrase enzymes are recognized for their ability to increase the flexibility to use less digestible energy sources in feed formulations without compromising animal performance in several markets.
Currently, more than 20 products containing xylanase activity, either alone or in combination with other enzymes, and these have been approved by the European Union (EU) for the use in pig diets. As the EU requires enzyme suppliers to prove the efficacy of their products in at least three scientific animal trials per species and stage of production, there is a significant amount of data out there regarding carbohydrases in pig diets.
Nevertheless, there are other markets that are still skeptical about the use of carbohydrase enzymes in pig diets. This can to some extent be attributed to lack of experience and confidence in formulating with alternative energy sources. It also is attributable to misconceptions or myths about carbohydrase enzymes, lack of understanding in terms of their appropriate application and unrealistic expectations, which can all result in disappointment.
Myth No.1 - Carbohydrases improve pig performance regardless of diet composition
Carbohydrases break down starch or indigestible fibrous material in the pig's digestive tract and make more energy available for the animal to absorb. Like any other enzyme, carbohydrases are substrate specific. This means that in order for the enzyme to provide a benefit in the formulation of pig diets, the diet must contain the relevant specific substrate for the enzyme to work on (see, Table 1 for the major types of carbohydrase enzymes used in pig diets and their corresponding substrate). Depending on the diet ingredients and the total level of dietary substrates, the enzyme will have more or less to work on in the digestive tract of the animal.
It is generally accepted and expected that the value of the enzyme will increase with the level of substrate in the diet. For example, Table 2 shows how the level of arabinoxylans, a substrate for xylanase enzymes, changes with the composition and complexity of the diet. However, there are indications that the response to the enzyme will to some extent also depend on the energy stress the animal is experiencing. So factors limiting the dietary energy uptake, such as low voluntary feed intake in the young pig, total dietary energy content, heat stress and feeder space limitations in grow-finishing pens can influence the magnitude of the response to the enzyme.
Myth No.2 - All carbohydrases are the same
Carbohydrases such as xylanase, beta-glucanase and amylase can be produced from a range of plants, animals and microorganisms. Although particular types of enzymes, such as xylanase, share a common substrate (arabinoxylan) their substrate affinities and activities can differ widely. They also can differ in their pH optima. This will affect their activity in the digestive tract of the pig, which can again have an overall impact on the bio-efficacy of the enzyme.
The characteristics of xylanases are determined by the type of organism they are being produced from. Xylanases commonly used in the feed industry are produced by Aspergillus niger, which is fungal, Trichoderma reesei
or Bacillus subtilis, which are bacterial. The pH optima of bacterial xylanases are in general slightly higher than the pH optima of fungal xylanases. The enzymes can also differ in heat stability, which in turn affects their ability to withstand processing conditions during pelleting of feed.
To improve their inherent heat stability, enzymes can either be manipulated to this end or a coating can be applied to provide the enzyme with protection from heat. Depending on the methodology and technologies applied, there will be additional heat resistance differences between commercial enzymes.
Myth No.3 - The response to xylanase added to wheat is high regardless of wheat quality
Many factors can influence the feeding value of wheat and can vary from harvest to harvest, making it a highly variable feed ingredient. Data from the United Kingdom, Canada and Australia has shown the digestible energy content of different wheat samples can typically vary by as much as 1.3MJ/kg.
The problem for pig producers is that variability in wheat quality will translate into variability in pig performance. In a trial conducted in the United Kingdom, six different wheat varieties were grown on the same plot of land and incorporated into otherwise identical pig diets. There was an 18 percent variation in young pig growth rate between different wheat samples and a difference in feed conversion ranging from 1.28 to 1.47.
Trials including a xylanase in diets differing in wheat quality have shown that the enzyme is able to smooth out the variation in pig performance. However, the effect was greater on the low quality wheat compared to the medium quality wheat (see Table 3).
Myth No.4 - Carbohydrases are only relevant to the EU
Northern European countries traditionally feed high levels of wheat and barley in pig diets and therefore, have high levels of substrate that can be dealt with by xylanase and beta-glucanase. But the same is also true for Canada and Australia. Countries that have traditionally been feeding more corn-based diets, have been forced in recent years to replace corn with cheaper energy sources to minimize the cost of diets.
Alternatives such as corn DDGS, corn germ meal, wheat middlings and wheat generally have a lower and/or more variable energy content compared to corn and contain greater levels of substrate for the enzymes to work on. In summary, the application of carbohydrase enzymes is becoming increasingly more relevant around the globe.
Myth No.5 - Xylanase never works in corn-based diets
The impact of xylanase on corn-based diets depends on dietary energy intake and whether some of the corn has been replaced with by-products. It also is about the magnitude of response. Table 4 shows how grower-finisher pigs in 13 Asian trials (both commercial and university-based) fed corn-based diets react to xylanase and the associated levels of arabinoxylans in those diets. The response was measured on top of diets that were down formulated in energy or in diets where corn was to some extent replaced by lower energy feed ingredients, such as wheat, wheat middlings and rice bran.
Recent scientific publications in the United States also indicate that xylanase application positively impacts performance in growing pigs fed corn-based diets and significantly improves energy digestibility (Myers and Patience, 2013). A trial with a different commercial xylanase showed performance enhancements in growing pigs fed corn based diets incorporating corn DDGS with a response similar to that seen in pigs fed wheat-based diets (Kiarie et al, 2013).
