Vasoconstriction of peripheral blood vessels is one of the hallmark symptoms of fescue toxicosis in cattle. Thus, it was hypothesized that exposure to ergot alkaloids would increase the pulmonary arterial pressure (PAP). The objectives of this study were to examine the relationship between PAP and different physiological parameters of cows grazing either endophyte-infected (EI) or novel-endophyte (EN) fescue, then evaluate changes in PAP and other physiological measurements in cows exposed to EI pastures and deemed as susceptible or tolerant based on animal performance. Pregnant Angus cows at 2 different locations grazed either EI or EN fescue pastures for 14 consecutive weeks starting in early April of 2022. Forage measurements were collected to assess ergot alkaloid exposure throughout the study. In addition to measuring PAP, weekly measurements and blood samples were collected to evaluate physiological responses to ergot alkaloid consumption. The Fescue Toxicosis Selection Method (FTSM) was used for a post hoc analysis to identify cattle as either tolerant (EI-TOL) or susceptible (EI-SUS) when challenged with ergot alkaloid exposure. Data were analyzed using a MIXED procedure of SAS with repeated measures. Cows grazing on EN pastures had greater mean PAP values than EI cows, (P < 0.01), whereas a location effect was identified when comparing both EI-TOL and EI-SUS groups (P < 0.01). Cows exposed to EN pastures had greater average daily gain (ADG) (P = 0.04) and progesterone (P4) concentrations (P < 0.01), and lower hair shedding scores (HSS; P < 0.01) than EI cows. The EI-TOL cows tended to have greater final body weight, ADG and had lower HSS (P < 0.01) than EI-SUS cows. While cattle consuming EI tall fescue exhibited classical physiological changes, the decrease in PAP of cattle consuming EI fescue was unexpected and contradicted the initial hypothesis. Furthermore, the FTSM provides a means to identify animals with superior performance in spite of the chronic exposure to ergot alkaloids. Continued investigations examining the interaction between ergot alkaloid exposure and cardiovascular parameters will lead to a fuller understanding of the disease and are pivotal for developing innovative strategies that enhance best management practices to help guarantee the sustainability of the U.S. beef industry.

中文翻译：

---

探讨羊茅中毒对安格斯奶牛肺动脉压的影响


外周血管收缩是牛羊茅中毒的标志性症状之一。因此，据推测，暴露于麦角生物碱会增加肺动脉压 （PAP）。本研究的目的是检查 PAP 与放牧内生菌感染 （EI） 或新型内生菌 （EN） 羊茅的奶牛不同生理参数之间的关系，然后评估暴露于 EI 牧场并根据动物性能被认为易感或耐受的奶牛的 PAP 和其他生理测量值的变化。从 2022 年 4 月初开始，2 个不同地点的怀孕安格斯奶牛连续 14 周在 EI 或 EN 羊茅牧场放牧。收集牧草测量值以评估整个研究过程中麦角生物碱的暴露情况。除了测量 PAP 外，还每周收集测量和血样以评估对麦角生物碱消耗的生理反应。羊茅中毒选择方法 （FTSM） 用于事后分析，以识别牛在受到麦角生物碱暴露攻击时是耐受 （EI-TOL） 还是易感 （EI-SUS）。使用 SAS 的 MIXED 程序和重复测量分析数据。在 EN 牧场放牧的奶牛的平均 PAP 值高于 EI 奶牛 （P < 0.01），而在比较 EI-TOL 和 EI-SUS 组时确定了位置效应 （P < 0.01）。暴露于 EN 牧场的奶牛平均日增重 （ADG） （P = 0.04） 和黄体酮 （P4） 浓度较高 （P < 0.01），脱发评分较低 （HSS;P < 0.01） 比 EI 奶牛。EI-TOL 奶牛的最终体重 ADG 往往高于 EI-SUS 奶牛，HSS （P < 0.01） 较低。 虽然食用 EI 高羊茅的牛表现出经典的生理变化，但食用 EI 羊茅的牛的 PAP 降低是出乎意料的，并且与最初的假设相矛盾。此外，FTSM 提供了一种识别尽管长期暴露于麦角生物碱但仍具有卓越表现的动物的方法。继续研究麦角生物碱暴露与心血管参数之间的相互作用，将有助于更全面地了解这种疾病，并且对于制定创新策略以加强最佳管理实践以帮助保证美国牛肉行业的可持续性至关重要。