Adaptation strategies to seasonal changes in environmental conditions of a domesticated horse breed, the Shetland pony (Equus ferus caballus)

Abstract

SUMMARYRecent 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 feedrestricted animals significantly decreased from a mean of 52.8±8. ). 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.

Saving energy during hard times: Energetic adaptations of Shetland pony mares

“…Interestingly, our results did not reveal any difference in the mean daily T v between summer and winter. However, the results of a previous study on subcutaneous temperature in the same animals showed distinct nocturnal reductions in subcutaneous temperature that were greater in food-restricted animals compared with animals fed ad libitum (Brinkmann et al, 2012). Studies in humans showed that acclimated indigenous people have the ability to slightly reduce their metabolism during cold nights by allowing intensive peripheral cooling and a slight reduction in body core temperature (Scholander et al, 1958;Hammel et al, 1959) while unacclimated non-indigenous people showed a decrease in skin 111815 temperature in combination with an erratic increase in nocturnal metabolic rate by shivering.…”

“…It has been postulated that these pronounced seasonal fluctuations in MR are based on a reduction in physical activity and the heat increment of feeding and are not dependent on any reduction of BMR (Mautz et al, 1992;Mesteig et al, 2000). However, studies on red deer (C. elaphus), Alpine ibex (Capra ibex ibex), Przewalski horses (Equus przewalski) and domesticated horses (Equus caballus) revealed a nocturnal hypometabolism that contributes to reduced energy expenditure in late winter when food availability is low (Arnold et al, 2004;Kuntz et al, 2006;Signer et al, 2011;Brinkmann et al, 2012). In these last studies, the assumption of a reduced MR as an adaptation strategy to food shortage and low T a was based on the measurement of activity, heart rate and T b or subcutaneous temperature.…”

Towards a mechanistic understanding of the responses of large terrestrial mammals to heat and aridity associated with climate change

“…Reducing energy intake to about 70% of maintenance energy requirements decreased the body core temperature of sheep (Ovis aries) by about 0.5°C [145] and rectal temperature of horses (E. ferus caballus) by 1°C [139]. Rectal temperature fell similarly in starved goats and sheep [146].…”

“…Pronounced seasonal fluctuations in metabolic rate, as indexed by heart rate, have been observed in moose, Alpine ibex (Capra ibex ibex), red deer (Cervus elaphus) and horses (Equus ferus caballus and E. ferus przewalskii) in winter [68,[136][137][138][139], when the animals have to cope with low quality and difficult to access (e.g., if covered with snow) plant material. In desert environments, food availability closely follows precipitation, so large desert mammals typically experience insufficient food not during winter, but during summer, at a time when they are not exposed to cold stress.…”

“…It is therefore not surprising that in addition to a lowered metabolic rate, lower rumen temperatures in Alpine ibex [137] and lower subcutaneous temperatures in red deer and horses [136,138,139] were evident in winter. Even in a benign African environment, free-living springbok exhibited lower body core temperature in a dry winter [141].…”