Inter and intra feed material variability of the contents in total and phytic phosphorus and of phytase activity

Abstract

Proper management of phosphorus nutrition and excretion requires a good knowledge of total phosphorus content, phytic phosphorus content and endogenous phytase activity of the feed ingredients. Total phosphorus content varies greatly between feed materials, from less than 1 g/kg (wheat straw) to more than 210 g/kg (some phosphates). Total phosphorus usually makes up about 20% of the mineral matter and the phosphorus / mineral matter ratio (P/MM) depends on the biological family of the feed material. For cereal grains and oilseeds (2 to 8 g/kg of total P), the removal of starch or oil results in a concentration of mineral matter in the by-product while P/MM remains fairly stable for a given species (20% for wheat, 10% for soybean). Plant feed materials other than seeds, grains and their by-products tend to have lower total phosphorus contents (less than 3 g/kg) that are less correlated with mineral matter content.

Phytic phosphorus makes up about 50 to 80% of the total phosphorus of plant feed materials, with a high intra-species variability (30-90% for wheat). Plant phytases are significantly present in rye (more than 5000 U/kg), wheat milling by-products, triticale, barley and wheat. Intra-species variability is also high (250-1000 U/kg for wheat).

Several studies have shown that the main factor of variation for the content in total and phytic phosphorus of cereals is the growing location (P or N fertilization, climate). Both types of phosphorus are also often linearly related. Endogenous phytase activity seems to be primarily determined by genetics, but, since it is also related to the growing location, it does not seem to be usable for genetic selection. It is not related to total or phytic phosphorus content. Plant phytases are heat sensitive and the effect of technology on phytase activity should be monitored at each stage of the feed manufacturing process. In addition, phytase activity is subject to large inter-laboratory variability. In any case, predicting phosphorus content and phytase activity is not easy and laboratory analysis is often required.