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Phytate in feed ingredients and potentials for improving the utilization of phosphorus in ruminant nutrition

Humer, E., Zebeli, Q.
Animal feed science and technology 2015 v.209 pp. 1-15
eutrophication, excretion, feed conversion, feed processing, feeds, fermentation, germination, hydrolysis, ingredients, phosphates, phosphorus, phytases, phytic acid, rumen, rumen microorganisms, ruminant nutrition, ruminants, seeds, solubility
Phosphorus (P) nutrition has received renewed interest due to its potential environmental effects in terms of eutrophication and the limitations of the global raw phosphate stores. At the same time, in ruminants, P has more known key functions in the body and rumen microbes than any other mineral nutrient. Thus, although continuous P supply is of crucial importance, dietary P supply should not exceed the requirement of the animal. Sound knowledge regarding availability of P from different feedstuffs is a prerequisite to optimize the supply of dietary P. Phosphorus is primarily stored in the form of phytates in plant seeds, thus potentially reducing its ruminal solubility and consequently availability in ruminants, in particular when rumen functioning is suboptimal. The enzyme phytase catalyzes the stepwise hydrolysis of phytate. In respect to ruminant nutrition there are five possible sources of this enzyme available for the animals: ruminal microbial phytase, endogenous mucosal phytase, large intestinal microbial phytase, plant phytase and exogenous microbial phytase. Latest studies showed that the ruminal microbial phytase does not enable complete hydrolysis of phytate-bound P, although it is more efficient regarding phytate hydrolysis compared to endogenous mucosal phytase. Furthermore, plant phytase activity varies greatly among species of plants. Approaches to reduce the phytate contents of concentrates are the supplementation of microbial phytase as well as the application of diverse feed processing techniques like germination, fermentation and the treatment of feeds with organic acids. However, further research is warranted to evaluate the potential of these technologies. The main focus herein is to review the available literature on the role of phytate in ruminant nutrition, its degradation throughout the gastrointestinal tract and opportunities to enhance the utilization of feed P and to reduce the excretion of this main polluting nutrient.