This study aimed to evaluate the effect of narasin withdrawal on wethers ruminal fermentation characteristics. Four wethers cannulated at the rumen were subjected to a 4 × 4 Latin Square experimental design. The trial lasted 144 days, divided into 4 periods of 36 days each. The diet was composed by 950 g/kg of coastcross hay and 50 g/kg of ground corn, used as a carrier for the narasin. The experimental diets were defined by frequency of narasin offer: 1) no feed additives (N0); 2) 13 mg of narasin/kg of DM every 24 h (N13); 3) 26 mg of narasin/kg of DM every 48 h (N26), and 4) 39 mg of narasin/kg of DM every 72 h (N39). The narasin was offered for 25 days, and at the last 11 days of each period, all the animals received the same proportion of forage and concentrate, but without narasin inclusion (withdrawal period). Last day of narasin offering was denominated day 0 and the first day of withdrawal day 1. The fed offer and orts were daily recorded to determine de DMI and nutrient intake. Ruminal fluid was collected 6 h after concentrate offering from d0 to d11 to determine ruminal pH, SCFA and ammonia nitrogen. There was no difference for dry matter intake among treatments after narasin withdrawal. There was no treatment and day interaction for total SCFA concentration, molar proportion of acetate, butyrate, isobutyrate, valerate, isovalerate and rumen pH. Treatment and day interaction after narasin withdrawal interactions was observed for molar proportion of propionate (P < 0.01), Ac:Prop ratio (P = 0.03) and ammonia nitrogen concentration (P = 0.02). The increase in molar proportions of propionate for all narasin-containing treatments compared with the control was no significant by day 5 after narasin withdrawal (P ≥ 0.13). After narasin withdrawal, all doses of narasin inclusion decreased Ac:Prop ratio until day 3 after withdrawal (P ≤ 0.05) when compared with control diet. Effect of narasin on ruminal ammonia nitrogen concentration remained until day 3 after withdrawal (P ≤ 0.04), from day 4 there was no treatments effect (P ≥ 0.11) on ammonia nitrogen concentration. The data obtained from the present study demonstrate that narasin has a prolonged effect after withdrawal from the diet, being observed an effect on ruminal fermentation characteristics within 4 days after narasin withdrawal. These data suggest that the residual effect of narasin can be used as strategic feeding in situations where daily supplementation is not possible. Additionally, concerning scientific research using reversal designs, there is a need for a minimum of 5 days of washout between the experimental periods.

这项研究旨在评估降糖素对韦瑟斯瘤胃发酵特性的影响。瘤胃中插入的四个纬纱经4×4拉丁方实验设计。该试验持续144天，分为4个阶段，每个阶段36天。日粮由950克/千克的沿海干草和50克/千克的磨碎玉米组成，用作奈拉辛的载体。实验饮食是根据花生素的供应频率来定义的：1）没有饲料添加剂（N0）；2）每24小时13 mg萘乐辛/ kg DM（N13）；3）每48小时（N26）26 mg鼻饲素/ kg DM（4），以及4）每72小时（N39）39 mg鼻饲素/ kg DM。提供了鼻素25天，并且在每个时期的最后11天，所有动物都接受相同比例的草料和浓缩物，但是没有包括鼻素（戒断期）。鼻饲的最后一天定为第0天，戒断的第一天定为第一天。每天记录饲喂的饲喂量和饲喂量以确定de DMI和营养摄入量。浓缩液从d0到d11提供6小时后收集瘤胃液，以确定瘤胃的pH，SCFA和氨氮。麻醉素戒断后各处理间干物质摄入量无差异。总的SCFA浓度，乙酸盐，丁酸盐，异丁酸盐，戊酸酯，异戊酸酯和瘤胃pH值的摩尔比均无处理，且无相互作用。观察到了在纳瑞辛戒断反应后的治疗和日间​​交互作用的丙酸酯摩尔比（浓缩液从d0到d11提供6小时后收集瘤胃液，以确定瘤胃的pH，SCFA和氨氮。麻醉素戒断后各处理间干物质摄入量无差异。总的SCFA浓度，乙酸盐，丁酸盐，异丁酸盐，戊酸酯，异戊酸酯和瘤胃pH值的摩尔比均无处理，且无相互作用。观察到了在纳瑞辛戒断反应后的治疗和日间​​交互作用的丙酸酯摩尔比（浓缩液从d0到d11提供6小时后收集瘤胃液，以确定瘤胃的pH，SCFA和氨氮。麻醉素戒断后各治疗之间的干物质摄入量没有差异。总的SCFA浓度，乙酸盐，丁酸盐，异丁酸盐，戊酸酯，异戊酸酯和瘤胃pH值的摩尔比均无处理，且无相互作用。观察到了在萘乐辛戒断反应后的治疗和日间​​交互作用的丙酸酯摩尔比（P <0.01），Ac：Prop比（P  = 0.03）和氨氮浓度（P  = 0.02）。在丙酸为与对照组相比均含有甲基盐霉素，治疗的摩尔比例的增加是由甲基盐霉素戒断（后5天无显著P  ≥0.13）。支柱比直到3天停药（后：甲基盐霉素撤出后，所有剂量甲基盐霉素夹杂物降低AC P 与对照饮食相比，≤0.05）。保留在瘤胃氨氮浓度甲基盐霉素的效果直到3天停药（后P  ≤0.04），从第4天，没有治疗效果（P 氨氮浓度≥0.11）。从本研究中获得的数据表明，从饮食中撤出后，纳兰素具有延长的作用，观察到纳兰素戒断后4天内对瘤胃发酵特性的影响。这些数据表明，在无法每日补充的情况下，可以将萘乐辛的残留作用用作战略喂养。另外，关于使用逆向设计的科学研究，需要在实验期间之间至少冲洗5天。