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FEED ADDITIVES ▶▶▶


Raising the phytase podium


To improve phosphorus availability and tackle the antinutritional effects of phytates, phytases have been increasingly used in animal feeds over the past thirty years. Effective phytases are currently available on the market, but there is still room for improvement.


BY RACHAEL HARDY, DUPONT ANIMAL NUTRITION P


250 300


100 150 200


50 0 1


1.5 2 2.5 3 3.5 4 pH


Axtra PHY GOLD Competitor 4


Competitor 1 4.5 5 5.5 6 6.5 Competitor 2 Competitor 3 7


hosphorus plays a key role in metabolism and physi- ological processes such as bone development and maintenance, energy utilisation, protein synthesis, and efficient feed utilisation. Because monogastric


animals lack phytases – enzymes that break down phytates – these started being added to animal feeds to maximise the bioavailability of digestible phosphorus. After the first com- mercial phytase extracted from fungi came on the market in 1991, phytases were widely used in animal nutrition. Later on, microbial phytases replaced fungal phytases. This new generation of microbial phytases were preferred by the ani- mal feed industry due to their increased activity, proteolytic resistance and catalytic efficiency.


Figure 1 - Comparative pH profile with five different phytases. pH profile (% activity versus activity at pH 5.5)


Boosting phosphorus dynamics Phytate is not hydrolysed in the phytase-free monogastric gut, so the natural sources of phosphorous available in feeds are not absorbed. To avoid phosphorus deficiency, inorganic phosphate is added to diets. However, this represents a finan- cial burden for producers as phosphate supplementation is generally provided through calcium phosphate, one of the most expensive nutrients added to feeds. Moreover, phytate has been shown to reduce animal growth performance. The antinutritional effects of phytate are linked to its ability to bind with protein and calcium and inhibit the activity of di- gestive enzymes, such as pepsin, leading to an increase in en- dogenous losses and shifting energy away from growth. Phytate also reduces nutrient digestibility within the small in- testine, and impairs the proper absorption of several miner- als, such as calcium, magnesium, iron and zinc. The phytate issue began to be tackled through phytase sup- plementation. Phytases break down the available phytate, thus capitalising on a source of phosphorus that would other- wise be unused, reducing the need to supplement diets with phosphate. But the benefits of phytases go beyond releasing phosphorus: they also play a significant role in reducing the negative impact of inorganic phosphorous excretion to the environment. The excess phosphorous in phytate is often ex- creted in manure, which is a source of environmental pollu- tion. Ultimately, phytases represent a win-win situation for both nutritional and environmental phosphorus-related is- sues. This led to the development of an array of different enzymatic options that enhance the nutritive value of plant-based animal feeds.


The ultimate phytase profile An ideal phytase should be active in the low-pH environment of the stomach to begin phytate hydrolysis as soon as possi- ble. It should also resist high temperatures during the pellet- ing process, and should have a high specific activity at physi- ological temperatures. The commercial phytases currently available perform differently in the laboratory, and thus vary in their effects on animal performance. The enzyme that cur- rently has the highest bioefficacy and activity at low pH is a Buttiauxella phytase, which acts twice as fast as its direct competitors to ensure that most of the phytate is hydrolysed in the early stages of digestion, which take place in gut


18 ▶ ALL ABOUT FEED | Volume 28, No. 4, 2020


% activity relative to pH 5.5 activity


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