Johnson J S, Bryant J K, Scharf B, Kishore D K, Coate E A, Eichen P A, Keisler D H, Spiers D E
Division of Animal Sciences, University of Missouri, Columbia, MO, 65211, USA.
Int J Biometeorol. 2015 Apr;59(4):385-96. doi: 10.1007/s00484-014-0850-4. Epub 2014 Jun 18.
Cattle of the same breed from different regions of the USA may have altered responses to heat stress and fescue toxicosis. Angus steers from Missouri (MO ANG, n = 10, 513.6 ± 13.6 kg BW) and Oklahoma (OK ANG, n = 10, 552.8 ± 12.0 kg BW) were fed a diet containing either endophyte-infected (E+, 30 μg ergovaline/kg BW/day) or endophyte-uninfected (E-, 0 μg ergovaline/kg BW/day) tall fescue seed for 23 days. Diet treatment began on day 2. Animals were maintained at thermoneutrality (TN, 19-22 °C, days 1-8) and then exposed to heat stress (HS, cycling 26-36 °C, days 9-22). On day 23, ambient temperature was returned to TN and used as a recovery day. Feed intake (FI) was measured daily, with rectal and skin temperatures determined six times daily. Feed intake reduction from pretreatment levels was greater (P < 0.01) for E + (13.9 ± 0.9 versus 11.9 ± 0.3 kg/day) compared to E - (12.6 ± 0.9 versus 12.4 ± 0.3 kg/day) steers over the entire TN period, regardless of Angus group. During HS, E + cattle had reduced FI (P < 0.02; 6.9 ± 0.2 versus 8.4 ± 0.2 kg/day) compared to E - animals, independent of region of origin. A greater decrease in FI (P < 0.01) was observed for OK (12.1 ± 0.3 versus 6.2 ± 0.2 kg/day) compared to MO ANG (12.2 ± 0.3 versus 7.9 ± 0.2 kg/day) when ambient temperature was increased from TN to HS. On day 13 and days 15-22, OK ANG (E+) had reduced FI (P < 0.01, -2.21 kg) compared to OK ANG (E-), while there was no effect on MO ANG. From day 12 to day 22 of HS, daily minimum temperatures for ear, rump, and tail skin were less for E + (P < 0.05) when compared with E-treated steers, signifying peripheral vasoconstriction in E + animals. This was supported by reduced shoulder and lower tail temperatures (P < 0.01) for E + compared to E-treated OK ANG on the recovery day. In summary, regional differences in the response to fescue toxicosis exist, with peripheral vasomotor effects becoming most evident when animals are subjected to rapid changes in their environment.
来自美国不同地区的同一品种牛对热应激和牛鞭草中毒可能有不同反应。将来自密苏里州（MO ANG，n = 10，体重513.6 ± 13.6千克）和俄克拉荷马州（OK ANG，n = 10，体重552.8 ± 12.0千克）的安格斯阉牛饲喂含内生菌感染（E +，30微克麦角缬氨酸/千克体重/天）或无内生菌感染（E -，0微克麦角缬氨酸/千克体重/天）的高羊茅种子的日粮23天。日粮处理于第2天开始。动物先在热中性环境（TN，19 - 22°C，第1 - 8天）饲养，然后暴露于热应激环境（HS，温度在26 - 36°C循环，第9 - 22天）。在第23天，环境温度恢复到TN并作为恢复日。每天测量采食量（FI），每天测定6次直肠温度和皮肤温度。在整个热中性期，无论安格斯牛群分组如何，与E - 阉牛（12.6 ± 0.9对12.4 ± 0.3千克/天）相比，E + 阉牛（13.9 ± 0.9对11.9 ± 0.3千克/天）采食量从预处理水平的减少幅度更大（P < 0.01）。在热应激期间，与E - 动物相比，E + 牛的采食量降低（P < 0.02；6.9 ± 0.2对8.4 ± 0.2千克/天），与起源地区无关。当环境温度从热中性升高到热应激时，与MO ANG（12.2 ± 0.3对7.9 ± 0.2千克/天）相比，OK ANG的采食量下降幅度更大（P < 0.01，12.1 ± 0.3对6.2 ± 0.2千克/天）。在第13天以及第15 - 22天，与OK ANG（E -）相比，OK ANG（E +）的采食量降低（P < 0.01，-2.21千克），而对MO ANG没有影响。在热应激的第12天至第22天，与E - 处理的阉牛相比，E + 牛耳部、臀部和尾部皮肤的每日最低温度更低（P < 0.05），表明E + 动物存在外周血管收缩。这在恢复日得到了支持，与E - 处理的OK ANG相比，E + 的肩部和尾部较低温度更低（P < 0.01）。总之，对牛鞭草中毒的反应存在区域差异，当动物环境快速变化时，外周血管运动效应最为明显。
