Davis Brittany E, Jacobs Alayna A, Flythe Michael D, Hamilton Tracy A, Ji Huihua, Schrick F Neal, Goodman Jack P
United States Department of Agriculture, Agricultural Research Service, Forage-Animal Production Research Unit, Lexington, KY 40506, USA.
Kentucky Tobacco Research and Development Center, University of Kentucky, Lexington, KY 40506, USA.
J Anim Sci. 2025 Jan 4;103. doi: 10.1093/jas/skaf304.
Livestock grazing endophyte-infected (E+) tall fescue can exhibit persistent systemic vasoconstriction and fescue toxicosis. Isoflavones in legumes, most notably red clover (RC), are known hypotensive agents. The objective of the experiment was to evaluate the effect of isoflavone supplementation via RC hay, every day or every other day (QOD), on average daily gain (ADG) of steers grazing E+ tall fescue pastures and their physiological recovery after grazing when managed on a non-toxic diet (28 d). In Spring 2018 (62 d) and 2019 (65 d), 36 Angus× steers were blocked by initial body weight (BW) into pastures (n = 6 pastures year-1) assigned to one of three supplement treatments: Dried distillers' grain with solubles (DDGS) only (CON; pasture + DDGS), 7.5% RC hay daily (based on 300-kg steer consuming 2.5%-BW; 7.5%-RC; pasture + DDGS + RC hay), or 7.5% RC hay QOD (7.5%-RC QOD; daily rotation of either: CON or 7.5%-RC). All supplements were isonitrogenous, and shrunk BW was collected at the start and end of the grazing period for determination of ADG. Each year, immediately after the grazing period, three steers were randomly selected from each pasture and moved to outdoor partially covered pens where they were fed a non-toxic diet for a recovery period of 28 d. The caudal artery of each steer was imaged immediately after grazing and then every 7 d over the recovery period using Doppler ultrasonography to monitor artery luminal areas (CAA). Jugular blood samples were collected immediately after grazing and on day 28 of recovery for determination of serum prolactin. Data were analyzed using the Mixed procedure of SAS with repeated measures, and significance was set at P ≤ 0.05. Steer ADG was greater with 7.5%-RC daily or QOD (7.5%-RC: 0.77 kg d-1; 7.5%-RC QOD: 0.83 kg d-1), compared to CON (0.55 kg d-1; P < 0.01). Isoflavone supplementation via RC hay during the grazing period resulted in 2.5× larger CAA and higher serum prolactin concentrations immediately after grazing and over the recovery period, respectively, compared with CON steers (P < 0.05). Furthermore, steers supplemented with 7.5%-RC during the grazing period were never vasoconstricted over the recovery period, but CON steers did not exhibit CAA recovery until day 21 (P < 0.05). Supplementation of isoflavones via RC hay daily or QOD is an effective management strategy to improve ADG in cattle grazing E+ tall fescue pastures and reducing the time required for physiological recovery post-grazing.
放牧感染内生真菌（E+）的高羊茅的家畜可能会出现持续性全身血管收缩和高羊茅中毒。豆类中的异黄酮，尤其是红三叶草（RC），是已知的降压剂。本实验的目的是评估通过每日或隔日（QOD）投喂RC干草补充异黄酮，对放牧E+高羊茅牧场的阉牛平均日增重（ADG）及其在无毒日粮管理下放牧后生理恢复情况（28天）的影响。在2018年春季（62天）和2019年春季（65天），36头安格斯×阉牛按初始体重（BW）进行分组，放入牧场（每年n = 6个牧场），分配到三种补充处理之一：仅添加干酒糟及其可溶物（DDGS）（CON；牧场 + DDGS）、每日添加7.5% RC干草（基于300千克阉牛消耗2.5%体重；7.5%-RC；牧场 + DDGS + RC干草）或隔日添加7.5% RC干草（7.5%-RC QOD；每日轮流：CON或7.5%-RC）。所有补充剂的含氮量相同，在放牧期开始和结束时收集收缩后的体重以测定ADG。每年，放牧期结束后，立即从每个牧场随机挑选三头阉牛，转移到室外部分有遮盖的围栏中，在那里给它们投喂无毒日粮，恢复期为28天。在放牧后立即以及恢复期每隔7天，使用多普勒超声对每头阉牛的尾动脉进行成像，以监测动脉腔面积（CAA）。在放牧后立即以及恢复第28天采集颈静脉血样，以测定血清催乳素。数据使用SAS的混合程序进行重复测量分析，显著性设定为P≤0.05。与CON组（0.55千克/天；P < 0.01）相比，每日或隔日添加7.5%-RC组（7.5%-RC：0.77千克/天；7.5%-RC QOD：0.83千克/天）的阉牛ADG更高。在放牧期通过RC干草补充异黄酮，与CON组阉牛相比，分别在放牧后立即和整个恢复期导致CAA增大2.5倍以及血清催乳素浓度升高（P < 0.05）。此外，在放牧期添加7.5%-RC的阉牛在整个恢复期从未出现血管收缩，但CON组阉牛直到第21天才出现CAA恢复（P < 0.05）。每日或隔日通过RC干草补充异黄酮是一种有效的管理策略，可提高放牧E+高羊茅牧场的牛的ADG，并减少放牧后生理恢复所需的时间。
