Horse core body temperature and the effect of rugs on skin temperature.
Many horse owners rug their horses all year round, however, a preliminary study, warns that the ambient temperatures expected and the type of rug needs to be carefully considered as horses can easily overheat.
It has become routine (and even fashionable) for many domestic horses to be rugged all year round – in fly-sheets, all-weather turnouts, stable rugs, fleeces or perhaps even a onesie. Rugs can be useful in protecting horses in adverse weather conditions and from biting insects, however, until now, there has been no study into the effect of different types of rugs on a horse’s body temperature.
Like humans, horses have a ‘thermoneutral zone’ (TNZ) – the range of ambient temperatures where the body can maintain its core temperature stable solely through regulating skin blood flow and without expending energy.
Adult horses in mild climates can maintain their core body temperature without expending energy when ambient temperatures are between 5ºC and 25ºC.
Humans (naked), on the other hand, have a more limited TNZ of between 25ºC – 30ºC. This means that when we feel cold, horses are still well within their comfortable zone. Despite this, we tend to make decisions about rugging our horses based on whether we feel cold ourselves, so we may well be using a rug on our horse when it really is not necessary, and this can cause horses to overheat. Overheating under rugs is a serious welfare concern.
A team of students from Duchy College, UK set out to investigate how the use of rugs affects horse temperature, and therefore how this impacts horse welfare. M.S.c student Kim Hodgess presented her findings at the 14th International Society of Equitation Science (ISES) conference in Rome.
The research team studied horses who were routinely rugged as part of their management routine, ten kept stabled indoors and two at pasture.
- Three of the horses wore sweet itch rugs (lightweight, woven polyester, non-waterproof rug covering the majority of the horse’s body including the neck and belly),
- six wore fleece rugs with no neck,
- two wore light quilted rugs with no neck, and
- two control horses were unrugged (one stabled and one at pasture).
The surface temperature of each horse was taken by taping a small temperature data logger directly on to each horse, just below the point of their hip. The environmental temperature was also recorded using temperature data loggers attached to either the horse’s stable door or to a wooden mounting block in the pasture.
All temperatures were recorded every minute for twenty-four hours.
(Note: For this study the researchers focused on skin temperature, not core body temperature as a way to detect changes in thermoregulation. They explain that, while there is limited research on the correlation between skin temperature and core body temperature, taking core temperatures was avoided because it requires using invasive methods that may cause the horse stress. They based their decision on a previous study that had found consistent correlations between a prototype non-contact thermography device, a thermal imaging camera at the horse’s girth and flank, and rectal temperature. As skin temperature varies depending on whether the horse is trying to conserve or lose heat to maintain its core temperature stable, for the purpose of this study, skin temperature was used as a way to detect changes in thermoregulation and was not intended to provide a reflection of core body temperature.)
The results showed significant differences between the temperature of the horses wearing different rugs.
Those wearing sweet itch rugs had little change in their temperature. However, those wearing fleece and light quilted rugs were found to have a significant increase in surface temperature.
When the environmental temperature had fallen below the TNZ to 0.5ºC–4.5ºC, four rugged horses had surface temperatures between 24ºC–30ºC, compared to the control (unrugged) horses at 12.5ºC–18.5ºC.
- The horses wearing sweet itch rugs had an average temperature increase of 4.2°C,
- those wearing fleeces 11.2°C and,
- those wearing light quilted rugs had an average increase of 15.8°C.
When the ambient temperatures were between 5oC and 21oC – which are within the horse’s TNZ, the results were as follows:
- For horses wearing sweet itch rugs, the skin temperature increased by 4.2oC
- for horses wearing fleece rugs it increased by 8oC
- those wearing light quilted rug increased by 12.2oC
The researchers concluded that some types of rugs can significantly increase horse surface temperature and could, therefore, compromise the horses’ capacity to regulate their own temperature.
While the use of rugs and blankets is necessary for some horses, this study shows that selecting the right type and weight of rug for your horse and his/her individual conditions is vital. Appropriate use and application must be seriously considered to ensure the rugs do not have a detrimental impact on horse welfare.
Researcher Kim Hodgess says: “This study was interesting for me as it has left me asking many more questions about the welfare of rugged horses. Questions that remain unanswered are: do dark coloured sweet itch rugs increase horse temperature, do rugs interfere with mutual grooming and can skin condition deteriorate with prolonged use of rugs?
“Although this study found sweet itch rugs had no impact on thermoregulation, I feel further research with a larger number of horses, in hotter weather conditions, with a mix of dark and light coloured sweet itch rugs is required before we can be certain there are no negative impacts on equine welfare.
“I would like to continue this area of research, as there is a lot more that could be investigated. A greater understanding of the impact rugs have on horse thermoregulation would help inform our rugging descisions, which has the potential to improve horse welfare.”
Interestingly, a previous, pilot study by Barbara Padalino and colleagues presented at the 2017 Equitation Science Conference in Wagga Wagga, Australia, showed that lightweight, ripstop cotton rugs of the type commonly used as ‘summer rugs’ in Australia, increased rectal temperature and sweat production considerably compared to non-rugged horses. The study warned that, despite providing fly protection (horses showed less tail swishing and discomfort behaviours), cotton rugs can still cause horses to overheat when environmental temperatures exceed 25oC and there is no adequate shade. (Download the proceedings here.)
Further studies using larger sample populations, in a wider range of ambient temperatures, with more variety of rugs and, possibly, in different countries, are required before scientists get a better picture of the effect of all different rugs in different situations. But in the meantime, think twice before you rug and choose the type of rug wisely.
For another great article on rugging decisions click here.
Save the date of August 19-21 for the 2019 International Society for Equitation Science Conference being held in Guelph, Ontario, Canada. The theme of “Bringing science to the stable” will explore our relationship with horses through the past, present and future. Check the ISES website for conference updates https://equitationscience.com/conferences/.