Wilson K R, Abney C S, Vasconcelos J T, Vázquez-Añón M, McMeniman J P, Galyean M L
Department of Animal and Food Sciences, Texas Tech University, Lubbock 79409-2141, USA.
J Anim Sci. 2008 Aug;86(8):1951-62. doi: 10.2527/jas.2007-0793. Epub 2008 Apr 11.
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.
进行了三项试验，以评估饲喂2-羟基-4-（甲硫基）-丁酸（HMTBA）对育肥牛的生产性能、胴体特性以及连续培养系统中微生物发酵的影响。在试验1中，160头杂交阉牛（初始体重=385±10.3千克）被随机完全区组设计分配到4种处理中，包括对照组（0%HMTBA）或3种含HMTBA的日粮（0.069%、0.137%和0.204%；干物质基础）。随着日粮中HMTBA百分比的增加，末重（P=0.069）、调整至恒定屠宰率的末重（P=0.063）和总体平均日增重（P=0.099）呈线性下降趋势。随着HMTBA剂量增加，总体干物质采食量呈线性下降（P≤0.006）。除了随着HMTBA剂量增加，美国农业部精选级牛的百分比呈线性增加趋势（P=0.078）外，胴体特性方面未发现差异（P≥0.10）。在试验2中，80头杂交阉牛（初始体重=450±17千克）被随机完全区组设计分配到对照组（0%HMTBA）日粮或在50天内HMTBA浓度从0.036%逐渐增加到0.212%干物质的日粮中。含HMTBA的日粮有降低干物质采食量的趋势（P=0.132），但整个饲喂期的料重比（P=0.319）、胴体测量指标以及美国农业部质量等级（P≥0.149）在处理间无差异。在试验3中，使用连续培养发酵罐（每个处理n=5）来确定HMTBA（对照组与0.24%HMTBA）对微生物发酵的影响。处理间在瘤胃有机物质消化率、微生物氮合成、pH值、氨、挥发性脂肪酸的摩尔比例或选定长链脂肪酸的流出物浓度方面未检测到差异（P≥0.31）。这些结果表明，HMTBA以剂量依赖的方式降低了以蒸汽压片玉米为基础日粮的育肥牛的干物质采食量；然而，随着时间逐渐增加剂量似乎减轻了对干物质采食量的影响。日粮干物质中HMTBA含量为0.24%时，连续培养中未观察到微生物发酵有重大变化，这表明HMTBA对干物质采食量的影响不太可能与瘤胃消化或发酵的变化有关。
