Maîtrise des rejets de phosphore dans les effluents d'élevage

Abstract

Better knowledge is needed of animal requirements and dietary supply utilisation in order to control phosphorus (P) content in animal wastes. The methods of investigation are quite different in non-ruminant (swine and poultry) and ruminants. The assessment of requirements is generally based on a factorial approach (maintenance and production needing) even if a global method based on bone mineralisation may be performed in non-ruminants. The knowledge available allows to set more precise nutritional standards where requirements (and dietary supply) are expressed in apparent digestible P (swine) or true absorbed P (ruminants) instead of total P. In non-ruminants, the evaluation of digestive efficiency of dietary P needs information on phytate P utilisation. This latter may be markedly different following phytasic activity in feedstuffs, addition of microbial phytase and phytasic activity inactivation during feed processing. For these reasons, two apparent digestible P values (with unbroken or destroyed phytasic activity) are in the INRA-AFZ Table; in addition, equations are given to take into account microbial phytase addition. In ruminants, true absorption coefficients have been assessed from literature data for the main groups of feedstuffs. These approaches, which allow a better adequacy between animal requirements and p dietary supply, must lead to a substantial decrease in P run off in animal wastes.