title: Effects of 2-hydroxy-4-(methylthio)-butanoic acid on performance and carcass characteristics of finishing beef cattle and on fermentation in continuous culture.
abstract: Three experiments were conducted to evaluate the effects of feeding 2-hydroxy-4- (methylthio)-butanoic acid (HMTBA) on performance and carcass characteristics of feedlot cattle and on microbial fermentation in a continuous-culture system. In Exp. 1, 160 crossbred steers (initial BW = 385 +/- 10.3 kg) were assigned to 4 treatments consisting of control (0% HMTBA) or 3 diets containing HMTBA (0.069, 0.137, and 0.204%; DM basis) in a randomized complete block design. As the percent of HMTBA increased in the diet, final BW (P = 0.069), final BW adjusted to a constant dressing percent (P = 0.063), and overall ADG (P = 0.099) tended to decrease linearly. Overall DMI decreased linearly (P < or = 0.006) with increasing HMTBA dose. No differences (P > or = 0.10) were noted for carcass characteristics, except for a tendency (P = 0.078) for a linear increase in the percentage of cattle grading USDA Choice with increasing HMTBA dose. In Exp. 2, 80 crossbred steers (initial BW = 450 +/- 17 kg) in a randomized complete block design were assigned to a control (0% HMTBA) diet or to a diet in which the concentrations of HMTBA were gradually increased from 0.036 to 0.212% of DM over a 50-d period. The HMTBA-containing diet tended to decrease DMI (P = 0.132), but G:F (P = 0.319) for the overall feeding period, carcass measurements, and USDA quality grade (P > or = 0.149) did not differ between treatments. In Exp. 3, continuous culture fermenters (n = 5/treatment) were used to determine the effects of HMTBA (control vs. 0.24% HMTBA) on microbial fermentation. No differences (P > or = 0.31) were detected between treatments in ruminal OM digestibility, microbial N synthesis, pH, ammonia, molar proportions of VFA, or effluent concentration of selected long-chain fatty acids. These results suggest that HMTBA decreased DMI by feedlot steers fed a steam-flaked corn-based diet in a dose-dependent manner; however, gradually increasing the dose over time seemed to moderate effects on DMI. No major changes in microbial fermentation in continuous culture were observed with HMTBA at 0.24% of dietary DM, suggesting effects of HMTBA on DMI were not likely associated with changes in ruminal digestion or fermentation.
authors.affiliation: Department of Animal and Food Sciences, Texas Tech University, Lubbock 79409-2141, USA. k.wilson@ttu.edu
authors.forename: K R
authors.initials: KR
authors.lastname: Wilson
authors.forename: C S
authors.initials: CS
authors.lastname: Abney
authors.forename: J T
authors.initials: JT
authors.lastname: Vasconcelos
authors.forename: M
authors.initials: M
authors.lastname: Vázquez-Añón
authors.forename: J P
authors.initials: JP
authors.lastname: McMeniman
authors.forename: M L
authors.initials: ML
authors.lastname: Galyean
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001823:Body Composition / Q000187:drug effects*; D002417:Cattle / Q000254:growth & development*; D004032:Diet / Q000662:veterinary; D004063:Digestion / Q000502:physiology; D005285:Fermentation; D008715:Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology; D015430:Weight Gain / Q000187:drug effects
chemical_list: C008391:alpha-hydroxy-gamma-methylmercaptobutyric acid; D008715:Methionine