Equine Jet Lag

Almost all life on earth is influenced by the daily cycles of light and dark brought about by the presence of the sun and the continuous rotation of our planet around its own axis. From the simplest algae to mammals, nearly all organisms have adapted their lifestyle in such a way that they organize their activities into 24-hour cycles determined by sunrise and sunset. Jet lag occurs due to an abrupt change in the light dark cycle resulting from travel across multiple time zones. This in turn causes de-synchronization between an organism's physiological processes and the environment.

The consequences of jet lag for the equine athlete have become more relevant in recent times due to increased travel of performance horses across multiple time zones for international competition. The effects of jet lag are significantly more detrimental for an athlete hoping to perform optimally in a new time zone.

All mammals possess a "master" circadian clock that resides in a specific area of the brain. Here diverse physiological processes, such as blood pressure, heart rate, wakefulness, hormone secretion, metabolism, and body temperature, are regulated. Each of these processes is in turn affected by time of day. During daylight hours, the eye perceives light, and the light signals travel to the brain where they activate a number of important genes. These "clock" genes are responsible for relaying signals conveying the time of day information to the rest of the body. Jet lag results in the acute disruption of each one of these processes.

Recent advances in the field of chronobiology have shown that a molecular clock functions in almost all tissues and that the activities of possibly every cell in a given tissue are subject to the control of a clockwork mechanism, which is ultimately controlled by the environmental light-dark cycle.

Research being conducted at the University of Kentucky's Maxwell H. Gluck Equine Research Center has resulted in successful isolation of a number of "clock" genes. A comparison of these equine-specific genes with their human counterparts has revealed an unusually high similarity between these two species at the DNA level.

Based on this similarity, information on the effects of transmeridian travel derived from studies on human performance can be used to provide guidelines to horse trainers.

In human studies, results clearly demonstrate significant disturbances in heart rate, respiratory rate, body temperature, evaporative water loss, and psychological function following intercontinental flights consisting of eastward or westward journeys across multiple time zones.

One study using fit human subjects examined performance times before and after an eastward journey across six time zones. Performance times for a 270m sprint were slower for the first four days following translocation as were times for a 2.8km run on the second and third days. This can be explained by the fact that the athletes' internal body rhythms, including several neuromuscular, cardiovascular and metabolic variables, and indices of aerobic capacity, are out of synchrony with the environmental light dark cycle following a transmeridian journey.

The severity of the jet lag effects can depend on a number of factors. These include the ability to preset the bodily rhythms before flying, the number of time zones crossed, the direction of the flight, and individual variability.

Feeding schedules play an important role in entraining biological clocks, particularly within the digestive system. It is important to change both feeding times and exercise schedules to mimic the new time zone prior to travel, in order to shorten the amount of time required for resynchronization of digestive function and performance capacity upon arrival.

Lighting is also of paramount importance. Exposing animals to bright early morning light for several days prior to an eastward journey across multiple time zones--or extended hours of evening light prior to a westward journey--will help synchronize circadian rhythms to the new time zone prior to travel.

The greater the number of time zones traversed, the more severe the physiological disruption. For example, a flight from Britain to the East Coast of the United States, across six time zones, would require a significantly greater resynchronization time than a flight from the East Coast to the West Coast (three time zones) within the continental United States.

Major complications associated with long distance travel include pleuropneumonia, otherwise known as "shipping fever," dehydration, and colic. Studies carried out at Tufts School of Veterinary Medicine have revealed that even in cool conditions, horses will often lose 2 to 5 pounds of body weight for every hour they travel, as they do not like to drink while traveling. Care of horses during long distance transportation is an extensive topic that requires separate attention.

At the Maxwell H. Gluck Equine Research Center, preparations are under way to conduct several experiments that will simulate phase advances and delays in the lighting schedule of groups of horses, thus mimicking eastward and westward journeys so that the molecular and physiological effects of jet lag and the time duration of these effects can be investigated. The goal of this research is ultimately to provide practical guidelines to trainers so that measures can be taken to counteract the detrimental effects of jet lag on performance, therefore leveling the playing field for horses competing away from home.

Barbara Murphy, Graduate Research Assistant, 859/257-4757
Maxwell H. Gluck Equine Research Center, University of Kentucky, Lexington, Ky.

From Equine Disease Quarterly, funded by underwriters at Lloyd's, London, brokers, and their Kentucky agents.

About the Author

Equine Disease Quarterly

Equine Disease Quarterly is a quarterly equine disease research newsletter published by the University of Kentucky's Gluck Equine Research Center, and funded by underwriters at Lloyd's of London, brokers, and their agents.

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