273 Awardee Talk: A Perspective on Calcium and Phosphorus Nutrition: Where we are and the Opportunities Ahead

Abstract

Abstract Quantifying dietary calcium (Ca) and phosphorus (P) that can be used in the body of the animal is important for formulating nutritionally adequate diet and for efficient production of animal products. Historically, utilizable Ca and P in feedstuffs have been determined using the slope-ratio bioassays. The relative available Ca or P obtained from the assay is highly dependent on, among others, the available Ca or P in the reference source and the response criterion; and the measure is not usually additive in mixed feeds. The most common response criteria are bone ash and mineral concentration, or breaking strength, which tend to be labor-intensive and expensive, and very importantly do not provide estimates of mineral quantities voided by animals. The use of digestible in place of relative available overcomes some of the issues listed. For the formulation of diets that more accurately match requirement with dietary supply as well as proper quantification of excretion of P for environmental considerations, the use of relative available phosphorus as a currency is nebulous. Because colonic secretion or absorption of Ca has been shown in previous studies, it was important to, first, answer the question on whether there is a difference between Ca digestibility determined by the ileal cannulation technique or the total tract digestibility method. Unlike in poultry where urine P contributes to excreta in total tract, there is no difference between ileal and total tract digestibility of P in swine. The prominence of literature on utilization of Ca and P has provided more clarity in the understanding of the intricate interactions among Ca, P, and phytase. Issues of variation require more investigation into method standardization as well as additivity of digestible Ca and P values in mixed diet.