McKeever K H, Eaton T L, Geiser S, Kearns C F, Lehnhard R A
Equine Science Center, Department of Animal Sciences, Rutgers - the State University of New Jersey, New Brunswick, USA.
Equine Vet J Suppl. 2010 Nov(38):220-7. doi: 10.1111/j.2042-3306.2010.00259.x.
Older horses have an increased risk of hyperthermia due to impaired cardiovascular function. While many studies have investigated thermoregulation in horses during exercise, none have investigated the effects of ageing.
To test the hypothesis that there is a difference in thermoregulation during exercise and plasma volume (PV) in young and old horses.
Study 1: 6 young (Y, 7.7 ± 0.5 years) and 5 old (O, 26.0 ± 0.8 years) unfit Standardbred mares (507 ± 11 kg, mean ± s.e.) ran on a treadmill (6% grade, velocity calculated to generate a work rate of 1625 watts) until core temperature reached 40 °C. Core (CT), skin (ST), rectal temperature (RT) and heart rate (HR) were measured every min until 10 min post exertion. Packed cell volume (HCT), lactate (LA) and plasma protein (TP) were measured in blood samples collected before, at 40 °C and every 5 min until 10 min post exercise. Sweat loss was estimated using bodyweight. Study 2: Plasma volume was measured in 26 young (8.2 ± 0.7 years) and 8 old (26.6 ± 0.7 years) Standardbred mares (515 ± 12 kg) using Evans Blue dye. Pre-exercise blood (rBV) and red cell (rRCV) volumes were calculated using PV and HCT. Data analysis utilised repeated measures ANOVA and t tests and data are expressed as mean ± s.e.
Old horses reached 40 °C faster (998 ± 113 vs. 1925 ± 259 s; P < 0.05) with a greater HR at 40 °C (184 ± 6 vs. 140 ± 5 beats/min; P < 0.05) and greater sweat losses (P < 0.05). Heart rate did not differ (P > 0.05) post exercise. Age did not alter (P > 0.05) CT, ST, RT, LA, HCT or TP. Plasma volume was greater in Y vs. O horses (P < 0.05, 28.5 ± 1.4 vs. 24.1 ± 1.6 l) as was rBV (41.3 ± 2.0 vs. 35.3 ± 2.3 l) and rRCV (13.3 ± 0.6 vs. 11.1 ± 0.8 l).
Ageing compromises the ability to handle the combined demand of exercise and thermoregulation in part due to decreased absolute pre-exercise PV.
由于心血管功能受损，老年马匹体温过高的风险增加。虽然许多研究调查了马匹运动期间的体温调节，但尚无研究探讨衰老的影响。
检验年轻和老年马匹在运动期间体温调节及血浆容量（PV）存在差异这一假设。
研究1：6匹年轻（Y，7.7±0.5岁）和5匹老年（O，26.0±0.8岁）未经训练的标准赛马母马（507±11千克，均值±标准误）在跑步机上奔跑（坡度6%，速度设定为产生1625瓦的工作速率），直至核心体温达到40°C。运动前、达到40°C时以及运动后每5分钟直至10分钟，每分钟测量核心体温（CT）、皮肤温度（ST）、直肠温度（RT）和心率（HR）。在运动前、40°C时以及运动后每5分钟直至10分钟采集的血样中测量血细胞比容（HCT）、乳酸（LA）和血浆蛋白（TP）。通过体重估算出汗量。研究2：使用伊文思蓝染料测量26匹年轻（8.2±0.7岁）和8匹老年（26.6±0.7岁）标准赛马母马（515±12千克）的血浆容量。使用PV和HCT计算运动前血容量（rBV）和红细胞容量（rRCV）。数据分析采用重复测量方差分析和t检验，数据以均值±标准误表示。
老年马匹更快达到40°C（998±113秒对1925±259秒；P<0.05），在40°C时心率更高（184±6次/分钟对140±5次/分钟；P<0.05），出汗量更大（P<0.05）。运动后心率无差异（P>0.05）。年龄未改变（P>0.05）CT、ST、RT、LA、HCT或TP。年轻马匹的血浆容量大于老年马匹（P<0.05，28.5±1.4升对24.1±1.6升），rBV（41.3±2.0升对35.3±2.3升）和rRCV（13.3±0.6升对11.1±0.8升）也是如此。
衰老损害了应对运动和体温调节综合需求的能力，部分原因是运动前绝对PV降低。
