Consumption of ergot alkaloids from endophyte-infected tall fescue results in losses to the livestock industry in many countries and a means to mitigate these losses is needed. The objective of this study was to evaluate intra-abomasal infusion of the dopamine precursor, levodopa (L-DOPA), on dopamine metabolism, feed intake, and serum metabolites of steers exposed to ergot alkaloids. Twelve Holstein steers (344.9 ± 9.48 kg) fitted with ruminal cannula were housed with a cycle of heat challenge during the daytime (32 °C) and thermoneutral at night (25 °C). The steers received a basal diet of alfalfa cubes containing equal amounts of tall fescue seed composed of a mixture of endophyte-free (E─) or endophyte-infected tall fescue seeds (E+) equivalent to 15 µg ergovaline/kg BW for 9-d followed by intra-abomasal infusion of water (L-DOPA─) or levodopa (L-DOPA+; 2 mg/kg BW) for an additional 9-d. Afterward, the steers were pair-fed for 5-d to conduct a glucose tolerance test. The E+treatment decreased (P = 0.005) prolactin by approximately 50%. However, prolactin increased (P = 0.050) with L-DOPA+. Steers receiving E+ decreased (P < 0.001) dry matter intake (DMI); however, when supplemented with L-DOPA+ the decrease in DMI was less severe (L-DOPA x E, P = 0.003). Also, L-DOPA+ infusion increased eating duration (L-DOPA x E, P = 0.012) when steers were receiving E+. The number of meals, meal duration, and intake rate were not affected (P > 0.05) by E+or L-DOPA+. The L-DOPA+ infusion increased (P < 0.05) free L-DOPA, free dopamine, total L-DOPA, and total dopamine. Conversely, free epinephrine and free norepinephrine decreased (P < 0.05) with L-DOPA+. Total epinephrine and total norepinephrine were not affected (P > 0.05) by L-DOPA+. Ergot alkaloids did not affect (P > 0.05) circulating free or total L-DOPA, dopamine, or epinephrine. However, free and total norepinephrine decreased (P = 0.046) with E+. Glucose clearance rates at 15 to 30 min after glucose infusion increased with L-DOPA+ (P < 0.001), but not with E+ (P = 0.280). Administration of L-DOPA as an agonist therapy to treat fescue toxicosis provided a moderate increase in DMI and eating time and increased plasma glucose clearance for cattle dosed with E+ seed.

中文翻译：

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左旋多巴可减轻麦角生物碱引起的牛采食量减少

食用来自内生菌感染的高羊茅的麦角生物碱给许多国家的畜牧业造成损失，因此需要一种减轻这些损失的方法。本研究的目的是评估腹腔内输注多巴胺前体左旋多巴 (L-DOPA) 对暴露于麦角生物碱的公牛的多巴胺代谢、采食量和血清代谢物的影响。十二头装有瘤胃插管的荷斯坦公牛（344.9 ± 9.48 kg）被圈养，进行白天（32°C）热挑战和夜间（25°C）热中性循环。公牛接受含有等量高羊茅种子的苜蓿块的基础日粮，该种子由不含内生菌 (E─) 或感染内生菌的高羊茅种子 (E+) 的混合物组成，相当于 15 µg 麦角谷氨酸/kg BW，连续 9 天随后腹腔内输注水（L-DOPA─）或左旋多巴（L-DOPA+；2 mg/kg BW）另外9天。随后，将公牛配对饲喂5天以进行葡萄糖耐量测试。 E+治疗使催乳素降低（P=0.005）约50%。然而，L-DOPA+ 会增加催乳素（P = 0.050）。接受 E+ 的阉牛干物质采食量 (DMI) 降低 (P < 0.001)；然而，当补充 L-DOPA+ 时，DMI 的下降不太严重（L-DOPA x E，P = 0.003）。此外，当公牛接受 E+ 治疗时，L-DOPA+ 输注会增加采食时间（L-DOPA x E，P = 0.012）。 E+或L-DOPA+对进餐次数、进餐时间和摄入率没有影响(P＞0.05)。 L-DOPA+输注增加了(P＜0.05)游离L-DOPA、游离多巴胺、总L-DOPA和总多巴胺。相反，L-DOPA+使游离肾上腺素和游离去甲肾上腺素降低(P＜0.05)。总肾上腺素和总去甲肾上腺素不受L-DOPA+影响(P＞0.05)。麦角生物碱不影响（P>0.05）循环游离或总L-DOPA、多巴胺或肾上腺素。然而，E+ 使游离去甲肾上腺素和总去甲肾上腺素降低 (P = 0.046)。葡萄糖输注后 15 至 30 分钟的葡萄糖清除率随 L-DOPA+ 增加（P < 0.001），但随 E+ 增加（P = 0.280）。给予 L-DOPA 作为治疗羊茅中毒的激动剂疗法，使服用 E+ 种子的牛的 DMI 和进食时间适度增加，并增加血浆葡萄糖清除率。