Pfister J A, Stegelmeier B L, Gardner D R, James L F
ARS, USDA Poisonous Plant Research Laboratory, Logan, UT 84341, USA.
J Anim Sci. 2003 Sep;81(9):2285-93. doi: 10.2527/2003.8192285x.
Spotted locoweed (Astragalus lentiginosus var. diphysus) is a toxic, perennial plant that may, if sufficient precipitation occurs, dominate the herbaceous vegetation of pinyon-juniper woodlands on the Colorado Plateau. Six cow/calf pairs and four horses grazed a 20-ha pasture with dense patches of locoweed in eastern Arizona during spring 1998. Locoweed density was 0.7 plants/m2 in the pasture. Locoweed averaged 30.4% NDF and 18.4% CP. Concentrations of the locoweed toxin, swainsonine, fluctuated from 1.25 to 2 mg/g in locoweed. Horses ate more (P < 0.01) bites of locoweed than did cows (15.4 and 5.1% of bites, respectively). Horses generally increased locoweed consumption over time since they ate approximately 5% of bites in the preflower stage compared with 25% of bites in the pod stage. Cattle consumed almost no locoweed (< 1% of bites) until the pod stage, when they increased consumption to 15% of bites. Horses were very avid (approximately 65 to 95% of bites) in selecting the small quantities (approximately 40 to 150 kg/ha) of available green grass, and it appeared that their propensity to eat scarce green forage influenced their locoweed consumption as well. Horses ate relatively little dry grass, even when it was abundant, whereas cattle ate large amounts of dry grass until green grasses became more abundant. Calves began eating locoweed on the same day as their dams and ate approximately 20% of their bites as locoweed. Serum concentrations of swainsonine were higher (P < 0.05) in horses than in cattle (433 vs. 170 ng/mL, respectively). Baseline swainsonine was zero in all animals, but swainsonine was rapidly increased to above 800 ng/mL in serum of horses as they ate locoweed. Horses exhibited depression after eating locoweed for about 2 wk; after 5 wk of exposure, horses became anorectic and behaviorally unstable. Although limited in scope, this study indicates that horses should not be exposed to spotted locoweed.
斑点疯草（Astragalus lentiginosus var. diphysus）是一种有毒的多年生植物，如果降水充足，它可能会在科罗拉多高原的矮松-杜松林地的草本植被中占据主导地位。1998年春季，六对母牛/小牛和四匹马在亚利桑那州东部一片有密集疯草斑块的20公顷牧场上放牧。牧场上疯草密度为0.7株/平方米。疯草的中性洗涤纤维平均含量为30.4%，粗蛋白含量为18.4%。疯草毒素苦马豆素的含量在疯草中波动于1.25至2毫克/克之间。马采食的疯草口数比牛多（P < 0.01）（分别占总口数的15.4%和5.1%）。随着时间推移，马采食疯草的量总体上有所增加，因为它们在花期前采食的口数约为5%，而在结荚期则为25%。牛在结荚期之前几乎不采食疯草（< 1%的口数），结荚期时采食量增加到15%。马非常热衷于采食少量（约40至150千克/公顷）现有的青草，而且它们采食稀缺青草的倾向似乎也影响了它们对疯草的采食。即使干草充足，马采食的干草也相对较少，而牛则大量采食干草，直到青草变得更加充足。小牛与母牛同一天开始采食疯草，采食的口数中约20%为疯草。马血清中的苦马豆素浓度高于牛（P < 0.05）（分别为433和170纳克/毫升）。所有动物的苦马豆素基线值均为零，但马在采食疯草后，血清中的苦马豆素迅速升高至800纳克/毫升以上。马在采食疯草约2周后出现抑郁症状；暴露5周后，马变得食欲不振且行为不稳定。尽管本研究范围有限，但表明马不应接触斑点疯草。
