Phytates and phytases : their relevance in the feeding of pigs and poultry

Abstract

Plant, mainly phytic (2/3-3/4), phosphorus assumed to be poorly available usually provides 2/3 to 3/4 of the total P ingested by monogastric animals. Its availability may be improved either by adding microbial phytase to diets or by using phytase-rich cereal diets. Some cereals as wheat or rye or its by-products exhibit high phytase activity. Availability of plant P may vary from less than 20% for diets devoided of phytase activity to more than 60% for diets containing near 1000 microbial phytase units/kg. This may optimize the plant P utilization by pigs and poultry, saving inorganic P addition (up to 100%), thus markedly reducing (up to 50%) excreted P in manure. The main restriction to the extensive use of phytases, whatever their origin : phytase-rich cereals or added microbial phytases, depends on the temperature reached during feed processing. Some heating associated to pelleting process (70-80°C) partially (30 to 50%) inactivate the enzymatic activity, which is generally completely inactivated over 80°C. There is also a lack of screening of the relationships between cereal phytase levels and the corresponding phytic P availabilities.