Phosphorus Excretion of Feedlot Cattle Fed Diets Containing Corn or Distillers Coproducts

Samples were analyzed from three metabolism trials to evaluate the effects of dietary phosphorus (P) intake on P excretion in beef steers fed corn-based finishing diets. In Experiment I, ten steers were fed ten diets that involved two processing methods, whole and dry rolled corn and five corn sources, commodity, white, high oil, high protein, and highoil-high-protein corn. In Experiment II, six steers were fed three diets that included three variations of protein supplementation to meet 70, 80, and 100% of the degradable intake protein requirements for growing steers. In Experiment III, ten steers were fed five diets including control, 4% or 8% distillers solubles, and 10% or 20% wet distillers grains. For all experiments total urine and feces, feed intake, and feed refused were measured during a 5-d collection period, following 9, 10 and 14-d of dietary adaptation for the three respective experiments. Dietary P concentration (% DM) and dietary P intake (g/d) ranged from 0.31 to 0.36 and 21.5 to 27.2, 0.28 to 0.29 and 19.8 to 21.2 and 0.29 to 0.40 and 22.9 to 34.5 in the three respective experiments. Total P excretion was significantly related to P intake, but there was considerable variation among steers in partitioning excretion of P in urine or feces. Urinary P excretion (g/d) ranged from 3.0 to 7.4, 3.1 to 4.3 and 4.3 to 7.5 in the three studies, respectively. Replacing corn grain with corn processing co-products increased P intake but did not significantly change excretion patterns.