Moseley W M, Meeuwse D M, Boucher J F, Dame K J, Lauderdale J W
Pfizer, Inc., Veterinary Medicine Research and Development, Kalamazoo, MI 49001, USA.
J Anim Sci. 2003 Nov;81(11):2699-703. doi: 10.2527/2003.81112699x.
The dose response of melengestrol acetate (MGA) on ADG (kg/d) and gain efficiency (gain/DMI, g/kg) was estimated in beef steers fed a finishing diet under commercial feedlot conditions. Melengestrol acetate is not approved for use in steers as a feed additive. The study design was five blocks of four pens (each pen was assigned a dose of MGA) with 166 to 200 steers per pen. Melengestrol acetate was fed to steers at 0 (n = 899, five pens), 0.1 (n = 900, five pens), 0.2 (n = 899, five pens), and 0.4 (n = 900, five pens) mg of MGA/steer daily. Pens within a block were slaughtered on the same day. Blocks 1 through 5 were fed MGA for 123, 122, 116, 124, and 138 d, respectively. The experimental unit was a pen of steers, and blocking was based on source of steers. The ADG was 1.81, 1.85, 1.80, and 1.83 kg/d for steers fed 0, 0.1, 0.2, and 0.4 mg MGA per day, respectively. For ADG, the dose was significant, but neither linear nor quadratic effects were significant. Compared with steers of the control group, ADG was greater for steers fed 0.1 mg MGA (P < 0.01). Feed efficiencies were 170, 173, 171, and 172 g/kg for steers fed 0, 0.1, 0.2, and 0.4 mg MGA/d, respectively; however, no effects of dose (P = 0.19) or linear (P = 0.21) or quadratic (P > 0.60) effects were observed. There was no evidence for either positive or negative effects of MGA on DMI, hot carcass weight, dressing percent, quality grade, yield grade, back fat thickness, marbling score, longissimus muscle area, and incidence of dark cutter carcasses in response to feeding MGA to steers at doses of 0.1, 0.2, and 0.4 mg daily. The incidence of buller behavior (0.43 to 1.11%) was low and did not permit an accurate test of the clinical observations that feeding MGA to steers decreases the occurrence of buller steers. Melengestrol acetate fed to finishing beef steers produced small improvements in growth performance (ADG, 2.2%) at the 0.1 mg MGA dose, but none of the doses examined produced improvement in carcass quality or yield grade measurements.
在商业饲养场条件下，给育肥牛饲喂育肥日粮，评估醋酸美仑孕酮（MGA）对平均日增重（ADG，kg/d）和增重效率（增重/干物质采食量，g/kg）的剂量反应。醋酸美仑孕酮未被批准作为饲料添加剂用于公牛。研究设计为5个区组，每个区组有4个围栏（每个围栏分配一种MGA剂量），每个围栏有166至200头公牛。给公牛每日饲喂醋酸美仑孕酮的剂量分别为0（n = 899，5个围栏）、0.1（n = 900，5个围栏）、0.2（n = 899，5个围栏）和0.4（n = 900，5个围栏）mg/头。一个区组内的围栏在同一天屠宰。第1至5区组分别给公牛饲喂MGA 123、122、116、124和138天。实验单位是一群公牛，区组划分基于公牛来源。每日分别给公牛饲喂0、0.1、0.2和0.4 mg MGA时，其ADG分别为1.81、1.85、1.80和1.83 kg/d。对于ADG，剂量具有显著影响，但线性和二次效应均不显著。与对照组公牛相比，饲喂0.1 mg MGA的公牛ADG更高（P < 0.01）。每日分别给公牛饲喂0、0.1、0.2和0.4 mg MGA时，饲料效率分别为170、173、171和172 g/kg；然而，未观察到剂量（P = 0.19）、线性（P = 0.21）或二次（P > 0.60）效应。没有证据表明，每日给公牛饲喂0.1、0.2和0.4 mg MGA时，MGA对干物质采食量、热胴体重、屠宰率、质量等级、产量等级、背膘厚度、大理石花纹评分、腰大肌面积以及黑切牛肉胴体发生率有正面或负面影响。爬跨行为的发生率较低（0.43%至1.11%），无法准确检验关于给公牛饲喂MGA可减少爬跨公牛发生率的临床观察结果。给育肥牛饲喂醋酸美仑孕酮，在0.1 mg MGA剂量时生长性能（ADG）有小幅改善（2.2%），但所研究的任何剂量均未使胴体质量或产量等级指标得到改善。
