Phosphorus loads in waterways are a focus of environmental concern. Animal agriculture\'s contribution to this problem has been documented and efforts are focused on mitigating the issue. The effect of increasing amounts of mineral P supplementation on fecal P characteristics was studied in forage fed beef steers. Eight Hereford steers were fitted with total fecal collection bags and fed four diets with a low P grass hay and supplemented with increasing amounts of a mineral source of P, dicalcium phosphate. Dietary DM P concentrations were 0.10 (no P supplementation), 0.23, 0.34, and 0.45% P. Manure was sampled and dried, followed by analysis for total P and inorganic P (Pi). Blood was collected via jugular venipuncture following each collection period and plasma Pi was quantified. Total fecal P increased linearly with increasing dietary P concentration: 6.44, 10.6, 16.1, and 18.8 g/d (P < 0.0001). Fecal Pi increased linearly with increasing dietary P concentration: 1.58, 2.43, 2.74, and 3.84 g/d (P = 0.0119) Manure P solubility, however, did not increase with increasing dietary P concentration: 23.6, 22.3, 17.3, and 20.2% (P = 0.3646). Plasma Pi increased linearly with increasing dietary P (P = 0.0047). ADG and G:F were not affected by increasing dietary P content. Reducing or eliminating mineral P supplementation to forage fed beef animals is possible, if forage base proves to be adequate in P. Reducing dietary P reduces fecal P excretion and the pollution potential in ecologically sensitive areas like the Chesapeake Bay watershed. / Master of Science

The objectives of this study were to evaluate the effects of: (1) metaphylactic antibiotic administration (none or Excede on arrival); and (2) receiving diet crude protein levels (17.1 % or 11.9 % CP) on respiratory disease incidence, mortality, and growth performance of beef calves received into a stocker system as well as the influence of stocker treatment on feedlot and carcass performance. For the stocker phase, steers (n = 244) were stratified by BW and randomly assigned to 20 pens. Treatments were randomly assigned in a 2 x 2 factorial study design. At the conclusion of the stocker phase, 76 steers were sent to Tri County Steer Carcass Futurity in Lewis, IA. Metaphylactic treatment reduced the incidence of BRD and increasing CP in the receiving ration to 17.1 % resulted in greater ADG. Health, nutrition, and management during the stocker phase can impact feedlot and carcass performance.

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