Galyean M L, Ralphs M H, Reif M N, Graham J D, Braselton W E
Clayton Livestock Research Center, Department of Animal and Range Sciences, New Mexico State University 88415-9501, USA.
J Anim Sci. 1996 Apr;74(4):827-33. doi: 10.2527/1996.744827x.
Twelve Hereford steers (average BW = 231 kg) that had previously grazed native rangeland (Range) or irrigated winter wheat pasture (Wheat) were allowed to graze locoweed-infested rangeland from April 1 to June 9, 1994 (six steers/previous grazing treatment). Relative consumption level of locoweed and other forage classes was measured as observed bites per steer. Liver biopsy and whole blood samples were obtained from each steer before and after grazing. Liver samples were analyzed for several minerals by inductively coupled plasma-atomic emission spectroscopy, and whole blood samples were analyzed for Se. Liver concentrations of Ba (P < .001), Cd (P < .001), Ca (P < .01), Cr (P < .01), Ni (P < .001), Na (P < .01), and V (P < .001) were greater and concentrations of Mn (P < .09), P (P < .01), and K (P < .07) were less in Wheat than in Range steers. Liver concentrations of Fe, Mg, S, and Zn and whole blood Se concentrations did not differ (P > .10) between the two groups. Liver concentrations of Cr (P < .04) and Mn (P < .001) were less, and Fe concentrations were greater (P < .01), in samples taken after grazing than in samples taken before grazing of locoweed-infested range. Whole blood Se concentrations decreased (P < .01) from the beginning to the end of the grazing period, but this effect was not related (P > .15) to locoweed consumption. Changes in liver concentrations of minerals were compared relative to consumption levels of all forage classes in the locoweed-infested range. Liver concentrations of Cu decreased (r2 = .45; P < .02) as the percentage of bites consumed as locoweed increased, but concentrations after grazing locoweed-infested range were still within normal ranges. Changes in liver concentrations of other minerals were not related (P > .15) to consumption of locoweed. These data indicate that previous grazing history can have significant effects on liver mineral stores and that, under our conditions, consumption of locoweed by grazing beef steers altered liver Cu concentrations. Toxic effects of locoweed consumption would likely occur before Cu deficiency would be induced by grazing locoweed-infested range; hence, supplementation of Cu would seem unlikely to alter the course of locoweed toxicosis.
12头赫里福德阉牛（平均体重=231千克），此前曾在原生牧场（牧场组）或灌溉冬小麦牧场（小麦组）放牧，于1994年4月1日至6月9日被允许在疯草侵染的牧场放牧（每组6头阉牛）。疯草及其他饲草类别的相对采食量通过每头阉牛的观察采食量来衡量。在放牧前后从每头阉牛采集肝脏活检样本和全血样本。肝脏样本通过电感耦合等离子体原子发射光谱法分析几种矿物质，全血样本分析硒含量。与牧场组阉牛相比，小麦组阉牛肝脏中钡（P<0.001）、镉（P<0.001）、钙（P<0.01）、铬（P<0.01）、镍（P<0.001）、钠（P<0.01）和钒（P<0.001）的浓度更高，而锰（P<0.09）、磷（P<0.01）和钾（P<0.07）的浓度更低。两组之间肝脏中铁、镁、硫和锌的浓度以及全血硒浓度没有差异（P>0.10）。与在疯草侵染牧场放牧前采集的样本相比，放牧后采集的样本中肝脏铬（P<0.04）和锰（P<0.001）的浓度更低，铁浓度更高（P<0.01）。从放牧期开始到结束，全血硒浓度下降（P<0.01），但这种影响与疯草采食量无关（P>0.15）。将肝脏矿物质浓度的变化与疯草侵染牧场中所有饲草类别的采食量进行比较。随着作为疯草采食的采食量百分比增加，肝脏铜浓度下降（r2=0.45；P<0.02），但在疯草侵染牧场放牧后的浓度仍在正常范围内。其他矿物质肝脏浓度的变化与疯草采食量无关（P>0.15）。这些数据表明，先前的放牧历史可能对肝脏矿物质储备有显著影响，并且在我们的条件下，放牧的肉牛采食疯草会改变肝脏铜浓度。采食疯草的毒性作用可能在因在疯草侵染牧场放牧导致铜缺乏之前就会出现；因此，补充铜似乎不太可能改变疯草中毒的进程。
