Potchoiba M J, Nocerini M R, Carlson J R, Breeze R G
Department of Animal Sciences, Washington State University, Pullman, WA 99164-6320, USA.
Am J Vet Res. 1984 Jul;45(7):1389-92.
The metabolism of 3-methylindole (3MI), a ruminal degradation product of L-tryptophan, results in acute bovine pulmonary edema and emphysema. The effect of feeding an energy or protein supplement containing monensin on ruminal 3MI formation in pastured beef cattle was investigated. A luxuriant pasture of orchard grass was established in a field that was seeded 1 year before the start of the grazing period. This 4-ha pasture was cut, fertilized, divided into 2 equal plots, and then irrigated during a 22-day growth period. All cows were fed a restricted quantity of low-quality alfalfa hay for 33 days before the grazing period. Two experiments were conducted, using 38 cows (30 of the cows were used in experiment I and all 38 cows were used in experiment II). Cows in each experiment were randomly allotted to 2 groups. One group was designated in each experiment as the control group. The control group for experiment I was fed an energy supplement. The control group for experiment II was fed a protein supplement. The 2nd group in each experiment was given the same supplement as the respective control group with 200 mg of monensin added/! kg of feed. Supplements were fed on days - 1, 0, 1, 2, 3, 4, 5, 6, and 7 of each experimental period. Supplements were fed twice daily to provide 1 kg of supplement/cow. Cows were given access to orchard grass pasture on day 0 of each experiment. Ruminal fluid was collected daily for analysis of 3MI, indole, and volatile fatty acids. Ruminal fluid pH was recorded immediately after collection. Ruminal pH of all cows decreased from 7.3 to 6.2 during the first few days of grazing the orchard grass. Ruminal pH then gradually increased toward neutrality by experimental day 10. Significantly (P < 0.01) higher molar percentages of pro-pionate and lower (P < 0.01) molar percentages of acetate and butyrate were observed in the 2 groups fed the supplements with added monensin. These changes in propionate and acetate remained different (P < 0.01) from those of the controls for 10 days (or 3 days after the last monensin feeding). Compared with pregrazing ruminal concentrations of 3MI, the 3MI values were elevated (P < 0.01) by day 1 in all groups, except in the monensin-treated cows of experiment I. In experiment I, 3MI concentrations were highest on experimental days 5 and 10 in control and monensin-treated cows, respectively. In experiment II, 3MI concentrations peaked on day 4 for the control cows and day 6 for the monensin-treated cows. Monensin supplementation reduced (P < 0.05) 3MI formation on days 1 through 5 in experiment I and on days 1 through 3 in experiment II. Formation of 3MI was increased in ruminal fluid of all cows after an abrupt change to the pasture forage, but the rate of 3MI production was slower, and a lower peak concentration of 3MI was reached in cows fed monensin than was observed in the controls. These results indicate that monensin administration in either an energy or protein supplement effectively reduced ruminal 3MI formation in pasture-fed cattle.
3-甲基吲哚（3MI）是L-色氨酸的瘤胃降解产物，其代谢会导致急性牛肺水肿和肺气肿。本研究调查了在补充能量或蛋白质的饲料中添加莫能菌素对放牧肉牛瘤胃中3MI形成的影响。在放牧期开始前1年播种的一块地里，建立了一片茂盛的果园草牧场。这片4公顷的牧场在22天的生长期间进行了刈割、施肥、分成两个相等的地块，然后进行灌溉。在放牧期前，所有奶牛均限量饲喂低质量苜蓿干草33天。进行了两项试验，使用38头奶牛（30头奶牛用于试验I，所有38头奶牛用于试验II）。每个试验中的奶牛随机分为两组。每个试验中的一组被指定为对照组。试验I的对照组饲喂能量补充剂。试验II的对照组饲喂蛋白质补充剂。每个试验中的第二组给予与各自对照组相同的补充剂，但每千克饲料添加200毫克莫能菌素。在每个试验期的第-1、0、1、2、3、4、5、6和7天饲喂补充剂。每天分两次饲喂补充剂，每头奶牛提供1千克补充剂。在每个试验的第0天，让奶牛进入果园草牧场。每天采集瘤胃液，分析3MI、吲哚和挥发性脂肪酸。采集后立即记录瘤胃液pH值。在放牧果园草的头几天，所有奶牛的瘤胃pH值从7.3降至6.2。到试验第10天，瘤胃pH值逐渐向中性升高。在添加莫能菌素的两组补充剂饲喂组中，观察到丙酸的摩尔百分比显著（P<0.01）升高，乙酸和丁酸的摩尔百分比降低（P<0.01）。这些丙酸和乙酸的变化在10天内（或最后一次饲喂莫能菌素后3天）与对照组仍有差异（P<0.01）。与放牧前瘤胃中3MI的浓度相比，除试验I中经莫能菌素处理的奶牛外，所有组在第1天3MI值均升高（P<0.01）。在试验I中，对照组和经莫能菌素处理的奶牛在试验第5天和第10天3MI浓度最高。在试验II中，对照组奶牛在第4天3MI浓度达到峰值，经莫能菌素处理的奶牛在第6天达到峰值。在试验I中，莫能菌素添加在第1至5天减少了3MI的形成（P<0.05），在试验II中在第1至3天减少了3MI的形成。突然改为牧场饲料后，所有奶牛瘤胃液中3MI的形成均增加，但饲喂莫能菌素的奶牛3MI的产生速率较慢，且3MI的峰值浓度低于对照组。这些结果表明，在能量或蛋白质补充剂中添加莫能菌素可有效降低放牧牛瘤胃中3MI的形成。
