title: Dose-response relationship of tetronasin administered to grazing steers.
abstract: Two grazing experiments were conducted to evaluate the dose-response relationship of steers to the ionophore tetronasin. Bermudagrass-based pastures were grazed 126 d in Exp. 1, and annual ryegrass or an annual ryegrass-berseem clover mixture was grazed 112 d in Exp. 2. Tetronasin was administered in ground corn (.91 kg/hd) fed daily to provide dosages of 0, 7.5, 15, 30, 60 or 90 mg. One hundred forty-four steers (220 kg, Exp. 1; 196 kg, Exp. 2) were allocated to treatment groups of six steers within four initial weight blocks in Exp. 1 and within two initial weight blocks, assigned to two forage types in Exp. 2. Initial weight blocks were confounded with four pasture blocks, divided in six 1.35-ha paddocks. Treatment groups were rotated among paddocks within pasture block every 2 wk. Stepwise tetronasin addition resulted in a linear increase (P less than .05) in the proportion of propionic acid and a linear decrease (P less than .05) in the proportion of acetic acid and the acetic to propionic acid ratio in both experiments. Total VFA concentrations were not altered in Exp. 1 but they decreased linearly in Exp. 2 with tetronasin addition. Maximal observed improvement in daily gain (.1 kg) occurred at a dosage of 30 mg.hd-1.d-1 in Exp. 1 and 90 mg.hd-1.d-1 in Exp. 2. Daily gain increased linearly (P less than .06) with tetronasin level in both experiments.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Louisiana State University Agricultural Center, Baton Rouge 70893.
authors.forename: R N
authors.initials: RN
authors.lastname: Gates
authors.forename: L T
authors.initials: LT
authors.lastname: Roland
authors.forename: W E
authors.initials: WE
authors.lastname: Wyatt
authors.forename: F G
authors.initials: FG
authors.lastname: Hembry
authors.forename: J H
authors.initials: JH
authors.lastname: Bailie
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000494:pharmacology*; D002417:Cattle / Q000254:growth & development* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005232:Fatty Acids, Volatile / Q000032:analysis; D005663:Furans / Q000008:administration & dosage / Q000494:pharmacology; D007476:Ionophores / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D006109:Poaceae; D011897:Random Allocation; D012417:Rumen / Q000032:analysis; D015430:Weight Gain / Q000187:drug effects*
chemical_list: D000900:Anti-Bacterial Agents; D005232:Fatty Acids, Volatile; D005663:Furans; D007476:Ionophores; C055416:tetronasin