PART 3: CHANGES IN A HORSE’S
SYSTEMS DURING THE ADJUSTMENT
PERIOD WHEN MOVED TO A HOT
HUMID CLIMATE
What changes occur in the horse’s system during this process of acclimatisation?
Due to some of the past Olympic Summer Games being held in warm climates (e.g. Atlanta, Sydney, Beijing/Hong Kong, etc.), the experience gained and research carried out have proven a very valuable combination of information to determine the course necessary for horses to acclimatise to high heat and humidity. Essentially, the same heat regulatory adaptations that occur in the horse’s system in response to training occur in the acclimatisation process as the horse adapts to higher heat and humidity, but to a greater extent. These changes include an increase in the horse’s blood (plasma) volume which occurs after a week of exercising in hot, humid conditions. However, the changes in the horse’s sweating response, (including an increase in sweating rate and an earlier onset of sweating), may take up to two weeks of exercising in hot, humid conditions. Therefore, a minimum of at least two weeks or more in some cases may be necessary to allow the necessary changes in the horse’s system to occur.Furthermore, for these adaptations to take place, the horse must be exercised in the new environment. Simply exposing the horse to elevated heat and humidity will not confer the same adaptations. If the horse is unfit prior to arriving in the hotter environment, adaptations will take much longer. Untrained inadequately fit horses should not be subjected to exercise training in the heat until an adequate level of fitness has been achieved in cooler conditions.What is the usual time required for acclimatisation and adjustment of a horse moved to a hot humid climate?
The important process of acclimatisation of a horse moved to hot humid conditions is dependent on its heat regulating system as discussed in parts one and two on this subject in this column.High humidity is a particular challenge because horses, like humans, keep cool as their perspiration evaporates and are much more able to manage conditions of hot and dry than hot and humid.Horses must be allowed time to adjust to the new conditions to perform optimally, the same as an unfit horse must be conditioned to withstand the rigours of exercise.The acclimatisation period or length of time required to reach this stage will vary greatly depending on the horse, its health, temperament, transport tolerance, as well as fitness levels etc. But the intensity of the humidity and heat is a primary main factor influencing the time required for acclimatisation.As already mentioned, it generally takes a minimum of two weeks. Quite a few horses can require up to three weeks or more to allow their bodies to adapt and dissipate heat more efficiently. Basically, irrespective of the level of fitness, a horse that is transported to a hot humid climate and has not been acclimatised to work in these conditions is ill-prepared to deal with the added stress of the new environment.While high heat and humidity are not common to Ireland, all horses travelling to locations where they are a factor require acclimatisation for an adequate period of time.Do some horses have a greater difficulty in adjusting during the acclimatising period?
Yes. Again this varies depending on the horse’s temperament, the intensity of the humidity and heat, management and several other factors.During the acclimatisation period good management ensures that exercise intensity is usually reduced and the horse’s response to exercise is monitored closely. Increased sweating causes fluid and electrolyte losses to be much greater and the horse is likely to require larger water intakes in the hotter, more humid environment.Fitness: It is also very important that close attention is paid to the horse’s conditioning /fitness programme with the use of cardiac and respiratory recovery rates to guide advances in speed and intensity. Do some horses develop other extra problems when moved to hot humid climates to compete?
Some of these horses experience anhidrosis, which is an inability to sweat normally. In anhidrosis a horse stops sweating for no specific reason. There is no way to avoid this if the horse’s sweat glands fail to function but proper management of acclimatising the horse can help to prevent it. (A full article on anhidrosis will follow at a later date).
At what temperature is it dangerous for horses to compete?
As the ambient air temperature (30?C+) gets closer to the horse’s body temperature (38?C = normal horse temperature), it becomes increasingly difficult for the horse to dissipate heat. This is especially true if the humidity is also high, because the effectiveness of sweating is reduced. Obviously when not in work, horses will suffer much less from heat and will acclimatise more readily if they spend each night in a cool place, i.e. if stables are air conditioned. Another problem is in setting the most appropriate stable temperature; people may judge what is right for the horse by their own comfort level in a room temperature. However, because of horses’ larger size and their coats (and, therefore, the fact they lose heat more slowly), what can feel slightly chilly for us is comfortable for a horse. Approximately 25?C is considered to be the upper limit in temperature.The rationale for setting the stable’s temperature at approximately 23?C is that 25?C is considered to be the upper limit of a horse’s thermoneutral zone – above that the horse is likely to sweat or have an increased respiratory rate while in the stable. The indoor arena temperature will be set at approximately 21?C i.e. lower than the stables because horses are working. Like people, horses have varying susceptibilities to heat and heat-related illness can occur as a result of a very high body temperature or from exposure to a moderate to high body temperature for a long period. While acclimatisation may appear to be complete after 10-14 days, some less adjusted horses may not rest adequately or eat and drink properly and this can affect their health and performance. In addition to air conditioning in both the stables and the indoor training arena a cooling regime is usually recommended during exercise. For this purpose, a protocol combining acclimatisation with assisted cooling is the method of choice.