Jacobs J Luke, Leonard Elizabeth, Tharayil Nishanth, Duckett Susan K
Department of Animal and Veterinary Sciences, Clemson University, Clemson, SC 29634, USA.
Multi-User Analytical Laboratory, Department of Plant and Environmental Sciences, Clemson University, Clemson, SC 29634, USA.
Animals (Basel). 2025 Feb 11;15(4):513. doi: 10.3390/ani15040513.
Weaned Angus-cross steers (n = 69; body weight [BW] = 233 ± 29 kg) were used for the following purposes: (1) develop an assay to measure 3-methylhistidine (3MH) in blood samples to monitor changes in protein turnover, and (2) evaluate the effects of an implant (Revalor-G, 40 mg of trenbolone acetate, 8 mg of estradiol) or an implant plus individual supplementation via SuperSmart Feeder (SSF; C-Lock Inc., Rapid City, SD, USA) on animal growth, muscle growth, and nitrogen retention patterns in backgrounded beef steers. Steers were blocked by weight, trained to precision supplementation via SSF, and then assigned to one of three treatments: (1) grazing only [G], (2) grazing with implant [GI], or (3) grazing with implant plus individual animal supplementation via SSF at 0.75% BW [GIS] for 56 d of grazing study. Steers grazed a cowpea and pearl millet mixture until d 42, when forage became limiting, and steers were transitioned to an oat and annual ryegrass baleage. Steers were weighed and blood was collected every 14 d to determine plasma urea nitrogen (PUN), creatinine (CREAT), and 3-methylhistidine (3MH) concentrations. Ultrasound measurements of ribeye area (REA) were collected on d 0, 28, and 56. Data were analyzed using the GLIMMIX with treatment, day, and two-way interaction in the model. A novel, robust method for the determination of 3MH was developed and validated. The development of this 3MH method allows us to monitor changes in protein turnover in cattle over time, a metric which is related to production efficiency. A treatment-by-day interaction ( = 0.0050) was observed for BW and REA. Steer BW did not differ ( > 0.05) on d 0, 14, or 28 between treatments; however, on d 42, GI and GIS steers had a greater ( < 0.01) BW than G steers. On d 56, BW was greater ( < 0.0001) for GIS than GI and G, which not differ ( > 0.05). Total BW gain during the 56 d study was greater ( < 0.001) by 54% for GIS compared to GI or G. For GI, the total BW gain was greater ( < 0.01) by 18% compared to G. On d 56, the REA of GI and GIS steers was greater ( < 0.001) than of G steers. Steers in the GI treatment group had a greater PUN and PUN-CREAT ratio concentrations than the GIS steers. Both G and GI steers had greater 3-methylhistidine (3MH) concentrations compared to GIS steers on d 28. Our results demonstrate that the supplementation of implanted steers improves growth and improves nitrogen utilization during backgrounding on forage diets. This research illustrates that animal and muscle growth may be limited in grazing animals implanted with combination implants (estrogenic and androgenic compounds) when supplementation is not included.
断奶的安格斯杂交阉牛（n = 69；体重[BW]=233±29千克）用于以下目的：（1）开发一种测定血液样本中3-甲基组氨酸（3MH）的方法，以监测蛋白质周转的变化；（2）评估植入物（Revalor-G，40毫克醋酸群勃龙，8毫克雌二醇）或植入物加通过超级智能饲喂器（SSF；C-Lock公司，美国南达科他州拉皮德城）进行个体补充对育肥期肉牛的动物生长、肌肉生长和氮保留模式的影响。阉牛按体重进行分组，训练通过SSF进行精确补充，然后分配到三种处理之一：（1）仅放牧[G]；（2）放牧并植入[GI]；或（3）放牧并植入加通过SSF按体重的0.75%进行个体动物补充[GIS]，进行为期56天的放牧研究。阉牛采食豇豆和珍珠粟混合物直至第42天，此时牧草供应受限，阉牛转而采食燕麦和一年生黑麦草青贮料。每14天对阉牛称重并采集血液，以测定血浆尿素氮（PUN）、肌酐（CREAT）和3-甲基组氨酸（3MH）浓度。在第0、28和56天采集眼肌面积（REA）的超声测量数据。使用GLIMMIX对模型中的处理、天数和双向交互作用进行数据分析。开发并验证了一种新颖、稳健的3MH测定方法。这种3MH方法的开发使我们能够监测牛随时间的蛋白质周转变化，这一指标与生产效率相关。观察到体重和眼肌面积存在处理×天数交互作用（P = 0.0050）。在第0、14或28天，各处理间阉牛体重无差异（P>0.05）；然而，在第42天，GI和GIS组阉牛的体重高于G组阉牛（P<0.01）。在第56天，GIS组阉牛的体重高于GI组和G组（P<0.0001），而GI组和G组之间无差异（P>0.05）。在为期56天的研究中，GIS组的总体重增加量比GI组或G组高54%（P<0.001）。对于GI组，总体重增加量比G组高18%（P<0.01）。在第56天，GI组和GIS组阉牛的眼肌面积大于G组阉牛（P<0.001）。GI处理组阉牛的PUN和PUN-CREAT比值浓度高于GIS组阉牛。在第28天，G组和GI组阉牛的3-甲基组氨酸（3MH）浓度均高于GIS组阉牛。我们的结果表明，对植入的阉牛进行补充可改善育肥期采食牧草日粮时的生长并提高氮利用率。本研究表明，当不进行补充时，植入复合植入物（雌激素和雄激素化合物）的放牧动物的动物生长和肌肉生长可能会受到限制。
