Department of Animal Sciences, University of Göttingen, Göttingen, Germany.
J Exp Biol. 2012 Apr 1;215(Pt 7):1061-8. doi: 10.1242/jeb.064832.
Recent results suggest that the wild ancestor of the horse, the Przewalski horse, exhibits signs of a hypometabolism. However, there are speculations that domestic animals lost the ability to reduce energy expenditure during food shortage and adverse environmental conditions. Therefore, we investigated physiological and behavioural strategies employed by a robust domesticated horse breed, the Shetland pony, over the course of a year under temperate conditions by measuring ambient temperature (T(a)), subcutaneous temperature (T(s)), locomotor activity (LA), lying time, resting heart rate, body mass and body condition score. Ten animals were kept on pasture in summer and in open stables in winter; further, in winter the animals were allocated into one control and one feed-restricted group of five animals each to simulate natural seasonal food shortage. The annual course of the mean daily T(s) of all horses showed distinct fluctuations from a mean of 35.6±0.5°C, with higher variations in summer than in winter. Diurnal amplitudes in T(s) were highest (P<0.001) in April (12.6°C) and lowest in January (4.0°C), with a nadir around dawn and a peak around mid-day. The feed-restricted group had a significantly lower daily T(s) compared with the control group on cold winter days, with T(a) values below 0°C. Mean annual heart rate and LA followed T(a) closely. Heart rate of the feed-restricted animals significantly decreased from a mean of 52.8±8.1 beats min(-1) in summer to 29±3.9 beats min(-1) in winter and differed from the control group (P<0.001). Mean daily LA was lowest at the end of winter (7000 activity impulses day(-1)) and highest in summer (25,000 activity impulses day(-1)). Our results show that Shetland ponies exhibit signs of a winter hypometabolism indicated by reduced heart rate and T(s). Thus, domesticated horses seem to have maintained the capacity for seasonal adaptation to environmental conditions by seasonal fluctuations in their metabolic rate.
最近的研究结果表明，马的野生祖先普氏野马表现出代谢降低的迹象。然而，有人推测，在食物短缺和不利的环境条件下，家畜丧失了降低能量消耗的能力。因此，我们通过测量环境温度（T(a)）、皮下温度（T(s)）、运动活动（LA）、躺卧时间、静息心率、体重和身体状况评分，研究了在温带条件下，经过一年时间，强壮的驯化马品种设得兰小马在生理和行为策略上的表现。10 匹马在夏季被饲养在牧场上，在冬季被饲养在开放的马厩里；此外，在冬季，动物被分为对照组和限食组，每组各有 5 匹马，以模拟自然季节性食物短缺。所有马匹的平均每日 T(s)的年度变化明显波动，平均值为 35.6±0.5°C，夏季的变化比冬季大。T(s)的昼夜振幅在 4 月（12.6°C）最高（P<0.001），在 1 月（4.0°C）最低，在黎明前后达到低谷，在中午前后达到峰值。在寒冷的冬季，限食组的每日 T(s)明显低于对照组，环境温度低于 0°C。平均年度心率和 LA 与 T(a)密切相关。限食组的心率从夏季的平均 52.8±8.1 次 min(-1)显著下降到冬季的 29±3.9 次 min(-1)，与对照组有显著差异（P<0.001）。平均每日 LA 在冬季末（7000 次活动脉冲天(-1)）最低，夏季最高（25000 次活动脉冲天(-1)）。我们的研究结果表明，设得兰小马表现出冬季代谢降低的迹象，表现为心率和 T(s)降低。因此，驯化马似乎通过代谢率的季节性波动，保持了对环境条件的季节性适应能力。
