Department of Plant and Soil Sciences, University of Kentucky, Lexington 40546-0091.
J Anim Sci. 2012 Jul;90(7):2402-9. doi: 10.2527/jas.2011-4493. Epub 2012 Jan 27.
A 2-yr grazing experiment was conducted with crossbred steers (8 to 10 mo and with initial BW of 304 kg ± 34 kg in 2008 and 277 kg ± 24 in 2009) to evaluate animal performance and pasture responses of a late maturing tall fescue [Lolium arundinaceum (Schreb.) Darbysh; KYFA9301] population infected with the AR584 novel, non-toxic endophyte (Neotyphodium coenophialum; NE9301) as compared with Kentucky 31 fescue infected with the common toxic endophyte strain (KY31), 'Jesup' MaxQ fescue infected with the AR542 endophyte (MaxQ), and endophyte-free KYFA9301 (EF9301). Treatments were assigned for seeding in 1.0-ha pastures in a randomized complete block design with 3 replications. Pastures were grazed from 6 May to 23 July in 2008 (76 d) and 2 April to 25 June in 2009 (84 d). Each pasture was grazed with 4 tester steers and put-and-take steers were used to maintain forage mass at 2,500 ± 250 kg DM/ha. Shrunk BW was taken at initiation and termination of grazing each year. Rectal and skin temperatures were recorded, and jugular blood was collected each year at approximately d 28, 56, and study completion. Forage samples were collected at 2-wk intervals for analyzing CP, IVDMD, ADF, and NDF. Responses were analyzed with mixed models, and preplanned orthogonal contrasts were used to compare KY31 with non-toxic fescues, EF9301 vs. novel endophyte fescues, and NE9301 vs. MaxQ. All steer responses were similar (P > 0.10) among the non-toxic fescues. Average daily gains and total BW gain/ha for the 3 non-toxic fescues were greater (P < 0.001) than for KY31. Rectal/skin temperatures for the 3 non-toxic fescues were less (P < 0.001) and serum prolactin concentrations were greater (P < 0.01) than for KY-31. Pasture carrying capacity was greater (P = 0.003) for KY31 than the 3 non-toxic fescues and was greater for EF9301 (P = 0.017) than the 2 novel endophyte fescues. However, stocking rates (kg BW/ha) at the initial and midpoint days of grazing were similar (P > 0.40) among endophyte-fescue combinations, but by the end of the grazing season, stocking rate was greater (P < 0.001) for KY31 than for the non-toxic fescues and was greater (P = 0.053) for NE9301 than for MaxQ. Results indicated that NE9301 is as effective as EF9301 and MaxQ in improving BW gain and alleviating fescue toxicosis and that NE9301 can provide greater carrying capacities than MaxQ in late June and July.
2008 年和 2009 年，我们进行了一项为期 2 年的放牧实验，实验对象为杂交肉牛（8-10 月龄，初始体重 304 公斤±34 公斤），旨在评估迟熟高羊茅（Lolium arundinaceum（Schreb.）Darbysh；KYFA9301）与感染新型无毒内生真菌（Neotyphodium coenophialum；NE9301）的 AR584 高羊茅种群、感染常见有毒内生真菌菌株（KY31）的肯塔基 31 羊茅（KY31）、感染 AR542 内生真菌（MaxQ）的 Jesup 麦草（MaxQ）和无内生真菌的 KYFA9301（EF9301）的动物性能和牧场反应。在随机完全区组设计中，每个处理分配在 1.0 公顷的牧场上，有 3 个重复。2008 年 5 月 6 日至 7 月 23 日（76 天）和 2009 年 4 月 2 日至 6 月 25 日（84 天）进行放牧。每个牧场用 4 头试验牛进行放牧，用放牧牛来维持牧场每公顷 2500±250 公斤 DM 的草料量。每年放牧开始和结束时都会对收缩体重进行测量。每年大约在第 28、56 和研究结束时，记录直肠和皮肤温度，并采集颈静脉血液。每隔 2 周采集草料样本，分析 CP、IVDMD、ADF 和 NDF。使用混合模型分析结果，并使用预规划正交对比比较 KY31 与无毒羊茅、EF9301 与新型内生真菌羊茅和 NE9301 与 MaxQ。所有牛的反应在无毒羊茅之间相似（P＞0.10）。3 种无毒羊茅的平均日增重和总 BW 增重/公顷均大于 KY31（P＜0.001）。3 种无毒羊茅的直肠/皮肤温度较低（P＜0.001），血清催乳素浓度较高（P＜0.01），而 KY31 的直肠/皮肤温度较高，血清催乳素浓度较低。与 KY31 相比，KY31 的牧场承载能力更大（P=0.003），而与 2 种新型内生真菌羊茅相比，EF9301 的承载能力更大（P=0.017）。然而，在放牧开始和中期，不同内生真菌羊茅组合的放牧率（公斤 BW/公顷）相似（P＞0.40），但在放牧季节结束时，KY31 的放牧率大于无毒羊茅（P＜0.001），而 NE9301 的放牧率大于 MaxQ（P=0.053）。结果表明，NE9301 与 EF9301 和 MaxQ 一样有效，能提高 BW 增重，缓解羊茅中毒，而且在 6 月底和 7 月初，NE9301 提供的载畜量大于 MaxQ。
