Kohn C W, Hinchcliff K W
Department of Veterinary Clinical Sciences, Ohio State University, Columbus 43210, USA.
Equine Vet J Suppl. 1995 Nov(20):31-6. doi: 10.1111/j.2042-3306.1995.tb05005.x.
Physiological data were collected during two 3-day-event competitions: one (H) held in hot and the other (CL) in cool conditions. During H, ambient temperature and relative humidity were 2.5 degrees C-35 degrees C and 74-36% respectively, while during CL, ambient temperature and relative humidity were 7.8 degrees C-8.3 degrees C and 46%-41%, respectively. Rectal temperature, heart and respiratory rates were recorded on arrival at the event, at the end of Phase C and 6 min later, at the end of Phase D and for 30 min at 10 min intervals after each horse finished Phase D (Recovery Period). Because of the heat, the rest-pause during the Endurance Test was extended from 10 to 15 min for horses competing in H, and horses at H were aggressively cooled by repetitive bathing with ice water during the rest-pause and the 30 min Recovery Period. Heart rate was significantly higher (P < 0.05) at the end of Phase C in horses participating at H, as compared to those participating at CL. Heart rates were significantly decreased in both groups after 6 min in the rest-pause and by 10 min after the finish of Phase D. Rectal temperature were significantly higher in horses competing at H than in those competing at CL at the end of Phase C and 6 min later, and at 10 and 20 min after the finish of Phase D. In both groups, rectal temperatures decreased significantly during the first 6 min in the rest-pause and at 10 and 20 min after the finish of Phase D. Fifty-five of 79 (69.6%) horses starting Phase A at H completed Phase D, as compared to 23 of 28 (82.1%) of starters at CL (P > 0.05). Of 10 horses eliminated during the rest-pause at H, 3 were lame, 1 had exertional rhabdomyolysis, 4 were exhausted and 2 were lame and exhausted. Two horses were eliminated during the rest-pause at CL:1 was lame and the other had exertional rhabdomyolysis. There was marked individual variation in horses' responses to heat at H. Heat may have limited the effectiveness of evaporative cooling in horses at H, and resultant thermal stress probably contributed to exhaustion in horses unable to complete the Endurance Test. Aggressive cooling during the rest-pause and the Recovery Period was important to facilitate heat dissipation in horses at H. These measures were not necessary at CL.
生理数据是在两项为期3天的赛事中收集的：一项（H）在炎热条件下举行，另一项（CL）在凉爽条件下举行。在H赛事期间，环境温度和相对湿度分别为2.5摄氏度至35摄氏度和74%至36%，而在CL赛事期间，环境温度和相对湿度分别为7.8摄氏度至8.3摄氏度和46%至41%。在到达赛事场地时、C阶段结束时及6分钟后、D阶段结束时以及每匹马完成D阶段后（恢复期）每隔10分钟记录30分钟的直肠温度、心率和呼吸频率。由于炎热，耐力测试期间的休息时间从10分钟延长至15分钟，参加H赛事的马匹在休息时间和30分钟的恢复期内用冰水反复冲洗进行积极降温。与参加CL赛事的马匹相比，参加H赛事的马匹在C阶段结束时心率显著更高（P < 0.05）。两组马匹在休息6分钟后以及D阶段结束10分钟后心率均显著下降。在C阶段结束时、6分钟后以及D阶段结束10分钟和20分钟时，参加H赛事的马匹直肠温度显著高于参加CL赛事的马匹。在两组中，直肠温度在休息的前6分钟以及D阶段结束10分钟和20分钟时均显著下降。在H赛事中开始A阶段的79匹马中有55匹（69.6%）完成了D阶段，而在CL赛事中开始的28匹马中有23匹（82.1%）完成了D阶段（P > 0.05）。在H赛事休息期间被淘汰的10匹马中，3匹跛行，1匹患有运动性横纹肌溶解症，4匹疲惫不堪，2匹既跛行又疲惫不堪。在CL赛事休息期间有2匹马被淘汰：1匹跛行，另一匹患有运动性横纹肌溶解症。在H赛事中，马匹对热的反应存在明显的个体差异。炎热可能限制了H赛事中马匹蒸发散热的效果，由此产生的热应激可能导致无法完成耐力测试的马匹疲惫不堪。在休息时间和恢复期进行积极降温对于促进H赛事中马匹的散热很重要。在CL赛事中这些措施则没有必要。
