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We asked Arioneo to tell us a little about how horses regulate their temperature and the consequences for rugging. They certainly provide us a comprehensive response…
When autumn comes, it is normal practise to start to rug until the mild spring returns. However, it is difficult to create a universal rule defining when a horse should wear a rug and what thickness is required for the horse to be warmer. This topic is often debated as it depends on many parameters, such as the breed, age, physical condition, location (meadow, exposed grazing, stable) or geographical location. In order to appreciate the complexity of this problem, it is first necessary to understand how the horse adapts to face the cold.
A limited number of scientific publications have been interested in the natural regulation of body temperature in winter, known as thermoregulation. Below, a brief review summarises the salient points from the results of such research. Conducted and written by Dr Christine Briant, who is a Development Engineer at the IFCE (L’Institut français du cheval et de l’équitation/French Institute of Horse and Equestrianism) who works in partnership with ARIONEO as part of an ongoing collaboration.
Horse’s adapt in one of two ways, either by thermogenesis (heat production) or by thermolysis (loss of heat). Physiological mechanisms will modulate this adaptation or trigger responses which occur due to the heat transfer from the external environment to the horse’s body or vice versa, which is dependent on the outside temperature:
In a horse, skin, muscles, fat and hair all allow regulation. Regulation occurs dependent on the changes between the horse’s body and its environment.
When winter is approaching, especially if the horse is outdoors, hair grows longer and thicker to protect the horse from the temperature decrease. This photoperiodic phenomenon is the first progressive visible manifestation of cold adaptation.
Other mechanisms are involved in production of heat as an immediate response to cold exposure:
Evaporation is carried out by breathing (increases in the breathing rate) and sweating, which cools the temperature of the skin by evaporation. Conversely, exposure to cold will produce a decrease in respiratory rate, to decrease the heat loss.
Scientists call it the Thermal Neutral Zone or Thermal Comfort Zone or Minimum Thermoregulation Zone. This is the temperature range within the body that does not consume extra energy to maintain the internal body temperature.
If the body has to set up mechanisms to warm up (shivering or slowing down of the respiratory rhythm) or to cool (sweating, increased breathing rhythm), it means that the horse is out of its comfort zone. The lower limit of this zone is the lower critical temperature and the upper limit is the upper critical temperature.
In humans, the thermal comfort zone is very restrictive and is located at around 25°C.
In temperate regions, for unclipped horses, the thermal neutrality zone range is approximately between +5°C and +25°C.
However, it varies according to breed, morphology, age, health status and food intake. Thus, if the horse is outside during the natural decrease of the temperature in autumn, they will gradually adapt, by changing their coat, distributing their fat tissue differently, modifying their behaviour as well as their food intake. Horses need around 10 to 20 days to adapt to a temperature drop of around 15°C.
For new-born foals, the zone of thermal comfort is located between +16°C to +22°C.
Finally, attention should be paid to older horses whose thermoregulation functions might be impaired.
For clipped horses living in a temperate climate, a study showed that under +6°C, shivering might appear in some horses. In this way, the authors recommend using a rug or increase food intake under +6°C.
Moreover, some breeds or morphological types are more suited for hot or cold climes:
During transit in a trailer or horsebox, the temperature can be 10°C higher than the outside temperature. If a rug is necessary when boarding, during transit the horse’s comfort zone may change leading to a requirement to change the rug or remove the rug completely during transport. An inability to react to this change in need, may even create thermal stress.
Christine Briant link to the blog: https://comportementbienetreifce.wordpress.com
French Institute for the Horse and Equestrianism
Development and Research
We have read above that the thermal neutral zone has been studied and identified in scientific studies.
However, on a daily basis, each individual and many external parameters need to be taken into account, so it is pretty difficult to predict which rug will be the most appropriate and suitable for the approaching night for any given horse. Thus, two horses of different breeds living in the same place or two horses of the same breed living in different geographical areas may have very different thermoregulation processes and needs.
