Speakers: Prof K.E. Bach Knudsen, Prof M. Kidd, Dr J. Noblet  and Pierre-André Geraert

More about the feedase effect. Prof K.E. Bach Knudsen, Prof M. Kidd and Dr J. Noblet have discussed about the indigestible fraction of feed and its impact on the global feed digestibility.

Questions and answers session held during the live

Q: What elements or factors in feed and feed manufacturing destroy enzyme structural integrity?

Mainly feed processing with water vapor, pressure and temperature are stressful to protein structures and depending on their level and duration could significantly impair enzyme structures and thus efficacy.

Q: As substrate concentration increases is enzyme dose or rate of activity more important?

The efficacy of the enzymes is related to breaking down few bonds to decrease the mocelular size and restore the nutrient accessibility or decrease viscosity. Most of enzymes are not used to completely degrade a substrate like endogenous amylase releasing glucose, but are more used to decrease the length of the polysaccharides to reduce impact on viscosity or accessibility for the  endog enous enzymes. However, high doses of enzymes such as phytase need enough substrates to work on. Moreover NSP-enzyme dose response is usually curvilinear reaching a plateau irrespective of the substrate concentration.

Q: What are the anti nutrients specifically in corn?

More than anti-nutrients we should talk about low digestible or poorly digestible components that may affect the overall feed digestibility. As example the insoluble arabinoxylans highly ramified that you find in corn can reduce its nutritional value.

Q: About corn and soya bean diets. what is the percent % of cell wall fibers? and what are the exogenous enzymes required?

We have published many synthesis on those levels and recommend the following to get the best overview (Geraert et al., 2005, Dietary carbohydrates: a review of their physicochemical properties and digestibility in poultry and swine, 18 pp, Proc Eastern Nutrition Conference, ANAC, 10-11 May) as well as the most recent paper by Bach-Knudsen (Fiber and nonstarch polysaccharide content and variation in common crops used in broiler diets, Poult Sci, 2014, 93:2380-2393). Enzymes required to hydrolyse NSP from corn are endoxylanase, arabinofuranosidases, acetylxylan esterase, feruloyl esterase and glucuronidases. For soybean meal, a large range of enzymes is required including pectinases, xylanases, debranching enzymes.

Q: What is the different in anti nutrients between wheat and corn?

Most of the NSP structures exist in both cereals. However, the proportion of soluble NSP is higher in wheat than in corn and the arabinoxylans are more branched or ramified with arabinose residues in corn than wheat.

Q: You still haven´t mentioned the role of Proteases to increase total and aminoacids digestibility. Can you also explain the differences between birds and pigs regarding the mode of action of enzymes ?

Fundamentally exogenous enzymes are similar for both species but they may not release their effect at the same level of the digestive tract (pH, transit time…). Proteolytic enzymes are very abundant in the metabolism of our animal species, however, there is often a limited access to the protein in the vegetables for those endogenous enzymes. That's why NSP-enzymes having a range of enzyme activities have shown improvement in amino acid digestibility. Such an effect is not direct on the proteins but indirect giving more access of the chymotrypsine, pepsine... to the substrates.

Q: How this enzyme could behave in the rumen? Do you think it could improve feed digestibility in Dairy and beef cattle?

NSP-enzymes have already been evaluated in ruminants. They indeed improve the access to the fibres and may result in increased energy availability but have not yet often justified enough return-on-Investment.

Q: Beyond phytate and the specific compounds from soy, what anti-nutritional factors can you considered important in corn-wheat-soy diets?

Soybeans are riched in pectins, complex polysaccharide structures, and corn contain highly ramified arabinoxylans. Those structures limit the accessibility to the nutrients and are thus important to consider to improve feed digestibility?

Q: Organic acid can improve ndf digestion?

Improving the functioning of the intestine through lowering pH for instance will have an effect on feed digestibility. However, the animals do not possess the enzymatic activities required to truly digest fibres and improving the gut functioning will not generate new enzyme production such as xylanase or b-glucanase. Lowering pH especially in the hindgut might favour fibrolytic bacteria and subsequently improve NDF digestion. Unfortunately, the yield of such action might be very low.