title: Phosphorus requirement of finishing feedlot calves.
abstract: Dietary P supplied to feedlot cattle is important because an inadequate supply will compromise performance, whereas excess P may harm the environment. However, P requirements of feedlot cattle are not well documented. Therefore, 45 steer calves (265.2+/-16.6 kg) were individually fed to determine the P required for gain and bone integrity over a 204-d finishing period. The basal diet consisted of 33.5% high-moisture corn, 30% brewers grits, 20% corn bran, 7.5% cottonseed hulls, 3% tallow, and 6% supplement. Treatments consisted of 0.16 (no supplemental inorganic P), 0.22, 0.28, 0.34, and 0.40% P (DM basis). Supplemental P was provided by monosodium phosphate top-dressed to the daily feed allotment. Blood was sampled every 56 d to assess P status. At slaughter, phalanx and metacarpal bones were collected from the front leg to determine bone ash and assess P resorption from bone. Dry matter intake and ADG did not change linearly (P > 0.86) or quadratically (P > 0.28) due to P treatment. Feed efficiency was not influenced (P > 0.30) by P treatment and averaged 0.169. Plasma inorganic P averaged across d 56 to 204 responded quadratically, with calves fed 0.16% P having the lowest concentration of plasma inorganic P. However, plasma inorganic P concentration (5.7 mg/dL) for steers fed 0.16% P is generally considered adequate. Total bone ash weight was not influenced by dietary P for phalanx (P = 0.19) or metacarpal bones (P = 0.37). Total P intake ranged from 14.2 to 35.5 g/d. The NRC (1996) recommendation for these calves was 18.7 g/d, assuming 68% absorption. Based on performance results, P requirements for finishing calves is < 0.16% of diet DM or 14.2 g/d. Based on these observations, we suggest that typical grain-based feedlot cattle diets do not require supplementation of inorganic mineral P to meet P requirements.
authors.affiliation: Department of Animal Science, University of Nebraska, Lincoln 68583-0908, USA. geericks@unlnotes.unl.edu
authors.forename: G E
authors.initials: GE
authors.lastname: Erickson
authors.forename: T J
authors.initials: TJ
authors.lastname: Klopfenstein
authors.forename: C T
authors.initials: CT
authors.lastname: Milton
authors.forename: D
authors.initials: D
authors.lastname: Brink
authors.forename: M W
authors.initials: MW
authors.lastname: Orth
authors.forename: K M
authors.initials: KM
authors.lastname: Whittet
mesh_terms: D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D000831:Animals, Newborn; D015519:Bone Density / Q000502:physiology; D001842:Bone and Bones / Q000737:chemistry / Q000502:physiology*; D002417:Cattle / Q000254:growth & development / Q000378:metabolism*; D007408:Intestinal Absorption; D008297:Male; D009751:Nutritional Requirements; D009753:Nutritive Value; D016226:Phosphorus, Dietary / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*
chemical_list: D016226:Phosphorus, Dietary