Phosphorus in animal production systems

Phosphorus in agriculture is a limited resource, as well as a potential source of pollution, when used in excess as fertilizer. Animal production systems have a major contribution to phosphorus flow at the national level, animal manure contributing to about 50% of total supplies to agricultural land, with a large variability according to regions. Animal products also largely contribute to covering human nutritional needs, with on average 60% of total dietary phosphorus supplies. Efficiency of phosphorus retention by animals is highly variable among species. The highest efficiency is found in conventional broilers, followed by pigs, "label rouge" broilers and dairy cows, laying hens and beef cows expressing a lower efficiency. However, when considering the whole farming system, phosphorus pressure is generally lower in ruminant farming systems where more agricultural area is available for manure disposal. In recent years the determination of phosphorus requirements and its digestibility have been drastically improved in farm animals allowing an important reduction of phosphorus dietary supply and excretion, with in monogastric animals the additional contribution of the use of microbial phytase to improve digestibility. Compared to nitrogen, phosphorus loss to the environment is very low, and theoretically, it should be possible to achieve a very high efficiency of phosphorus utilization in agricultural/food systems. However, this would require a perfect recycling of phosphorus from animal manure and from animal by-product, which is not yet completely achieved.