Phosphorus nutrition of grazing cattle: a review

Phosphorus (P) is a widely studied element which is integral to many vital body functions. In ruminant nutrition, however, the degree of naturally occurring P deficiency in grazing cattle, the lack of uniformity in response to P supplementation, and even suggested P requirements have generated a great deal of confusion in the United States and around the world. Much of the confusion arises because animals have the ability to draw on skeletal P reserves when dietary P levels are inadequate. The mechanisms that control skeletal P withdrawal, the conditions that trigger withdrawal, and the rate and extent of withdrawal without affecting animal performance seem to be poorly understood. Another area of confusion involves the detrimental effect of P deficiency on feed intake which makes it unclear in many situations whether animal responses to P supplementation are due to P per se or simply to increased feed intake. This review attempts to discuss these and other important problems concerning the P nutrition of grazing cattle.