Reducing the Stress when Transporting Horses by Road and Air

Reducing the Stress when Transporting Horses by Road and Air

While some horses adapt well to transport, others do not, and being moved from one place to another can be highly stressful for them, whether they travel by air or by road.

Photo: Anne M. Eberhardt/The Horse

Reprinted from The Horse Report with permission from the Center for Equine Health, School of Veterinary Medicine, University of California, Davis (UC Davis). 

Horses have been transported across continents for centuries for many of the same reasons that they are transported today: competition, breeding, and commerce. They have traveled in ships, horse-drawn vehicles, trains, planes, and trailers and vans. Motorized conveyances were developed in the mid-1900s, and trailers or vans hauling pleasure, show, and race horses became essential in the horse industry.

The first known air transport of a horse reportedly was in the 1920s, and by the 1950s, horses were flying regularly between Ireland, England and France. The 1960s brought the “jet age,” with the first carriage of horses in a Boeing 707. Later, wide-bodied jets like the Boeing 747 could hold greater numbers of horses (up to 112) on charter flights. Throughout history, the management practices and other considerations in transporting horses have changed very little from ships to jets.

For horses that breed, show, or compete in athletic events, transport might be a necessary and frequent part of life. Air transport of horses is an obvious necessity for horses with international aspirations, but also is a viable modality for those going long distances within the United States. A 6-hour flight from New York to California can be a lot less stressful than a 72-hour van ride (five days). While some horses adapt well to transport, others do not, and being moved from one place to another can be highly stressful for them, whether they travel by air or by road.

Desmond Leadon, MA, MVB, MSc, FRCVS, RCVS, of the Irish Equine Centre in County Kildare, Ireland, is a leading authority on transport stress in horses. He has written extensively on the subject and includes a definition of stress in the context of transport: Stress occurs when a horse is required to make abnormal or extreme adjustments in its behavior or internal management (physiology) in order to cope with adverse aspects of its environment and management. While some adaptations to travel are normal, a measure of these adaptive responses can provide a better understanding of how stressful the circumstances are to the horse as well as its probable rate and duration of recovery.

The Irish Equine Centre has had an ongoing interest in transport research for the last 30 years. According to Leadon, “We have looked at stall design with air transport companies, aircraft manufacturers, and with aero engineers. We have studied airflow, temperature gradients, and environmental contamination within road transport vehicles and in aircraft carrying horses. It makes surprisingly little difference whether the vehicle has wings or wheels.” Rather, he proposes that managing the transit environment and a horse’s general health are key elements to delivering a horse to its destination in as good a condition as possible.

Factors involved in transport that contribute to stress include physical factors, psychological factors and environmental factors, as shown below.

Transport Stress: A Complex Response Involving Multiple Components

Physical Stressors Psychological Stressors Environmental Stressors
Loading and unloading Separation from the herd and familiar environment Fluctuations of temperature and humidity
Constant vibration and noise Exposure to strange environments and animals Altered and possibly inadequate ventilation
Noise Confinement Exposure to gases and particles from exhaust, urine, and feces
Loss of balance from accelerations and decelerations Lack of exercise or movement (particularly for older horses) Road or flight conditions
Deprivation of feed and water Schedule changes Intensity and/or fluctuations in light levels
Orientation to direction of travel   Dust
Head posture   Bedding
Decreased function of the immune system   Footing materials, traction
Lack of exercise or movement (particularly for older horses)   Disease or pathogens
Socialization with other traveling mates or isolation if traveling alone    
Length of journey    

Why is transport stress important? Horses stressed by transport are more susceptible to a variety of diseases, including pneumonia, colic, diarrhea, and laminitis. Additionally, transport stress could alter energy metabolism, which can affect the horse’s ability to perform or compete soon after transport. For these reasons, it is important for the horse’s welfare to minimize the stress of transport in every way possible by optimizing the transport environment. Take control of what can be controlled in order to reduce the chance of illness or injury in your horses.

Few studies on the effects of long-distance transportation of horses have been done. Yet, there have been numerous research studies reported on post-transit respiratory diseases in horses. To gain more insight into the physical responses of horses during transport, Carolyn Stull, MS, PhD, of UC Davis and Anne Rodiek, MS, PhD, emeritus professor at California State University, Fresno, teamed up to study the physiology of horses both during transport and recovery. The study was conducted using a commercial equine van that traveled the interstate highways of central California under typical hot and dry summer conditions.

The study subjects were 15 mature, healthy horses that were experienced travelers. Their physiological responses were documented during 24 hours of road transport, followed by a 24-hour recovery period during which horses rested in their individual stalls. It was important to study the recovery period to obtain information on how quickly the physiological responses return to pre-transit or baseline values. Here are some of the findings.

General health. Body weight, rectal temperature, and white blood cell count were measured as general indicators of health and the ability of the horses to handle the heat of the summer during transport. The horses generally lost about 6% of body weight, possibly due to heat dissipation, sweat loss, and decreased gut fill during transit, but they recovered half of their weight loss 24 hours after transit. This could support the notion that horses respond to heat stress during transit using their thermoregulatory mechanisms of sweating and increased respiration rate.

Dehydration. Hematocrit and total protein concentration are blood tests that are often used as indicators of dehydration in horses. These measurements increased during the duration of transport but returned to baseline values during the post-transit period. This indicated that dehydration was progressing with the duration of transport. Interestingly, during the last 12 hours of transport when the hematocrit levels peaked, the horses had consumed 91% of the water offered.

Muscle fatigue. Minimal muscular fatigue was found in the horses during the transit period. However, two serum enzymes with high activity in skeletal muscle and evaluated clinically in horses with muscular diseases are CPK and AST. In this study, CPK was slightly elevated after transport, and AST rose in response to transport and returned to baseline within 24 hours after transport. This indicates that there was muscle activity during transport probably due to maintaining balance.

Stress. During stressful situations such as exercise or transport, activation of the part of the brain that controls metabolic state (hypothalamic-pituitary-adrenal axis) results in an increased concentration of the hormone cortisol in blood circulation. The concentration of cortisol in these horses increased during loading and continued to rise throughout the 24-hour transit period, peaking at the termination of transit. After unloading, the stress of transportation ceased and cortisol concentration dramatically decreased.

The large increase of cortisol during transport influences the immune system, and its influence can be measured by the ratio of two types of white blood cells: the neutrophil:lymphocyte (N:L) ratio. This ratio also increased during transit and did not return to baseline within the 24-hour recovery period. This elevated N:L ratio contributes to disease susceptibility, such as pleuropneumonia, following long-term transport.

In other research conducted at UC Davis, Jim Jones, DVM, MS, PhD, has been studying transport stress in horses for the past 25 years. He has worked closely with international teams to identify factors that predispose horses to transport-associated respiratory disease (shipping fever) and to investigate biological indicators of stress in horses. Recently, he found that heart rate variability (HRV) could be a more sensitive indicator of physiologic stress than heart rate alone.

Heart rate variability is the variation in time between heartbeats. Some intervals are a little longer, some a little shorter. The lengthening and shortening of these intervals occurs regularly over intervals ranging from a few seconds to several minutes. These frequencies cannot be determined by looking at a recording but are identified using mathematical techniques (fast Fourier transform). The frequencies reflect how strongly different parts of the autonomic (unconscious) nervous system are activated—a balance between sympathetic (fight or flight) versus parasympathetic (rest and digest). HRV values can provide an idea of how strongly each part of the autonomic nervous system is stimulated and where the balance is.

Jones and his colleagues measured marked differences in the HRV responses of horses that were being transported compared with the same horses resting in their stalls. In a previous study, they noted that there was a modest occurrence of transport stress related to respiratory disease in horses traveling up to 12 hours. After that, the occurrence of shipping fever rises dramatically and in proportion to the duration of transport. So HRV, or the intervals between heartbeats, appears to be more suggestive of horses’ hormonal response to stressors, and this research tool will enhance future studies of how horses react to changes in their environment.

Shipping Fever and Other Illness

Shipping fever is the most common illness found in horses subjected to transport. It is a respiratory infection characterized by signs of depression, loss of appetite, fever, increased respiratory rate, nasal discharge, and coughing, and can rapidly progress to pleurisy and pneumonia.

Shipping fever can occur in as little as four to six hours after departure in all journeys. Initial signs of this condition can be seen relatively soon after takeoff in air journeys, which have been preceded by long road journeys or by long delays spent in a road vehicle while awaiting loading onto aircraft.

The incidence of shipping fever in long journeys can be 6% or higher. In any shipment of 16 or more horses, it is reasonable to anticipate and provide for one or more instances of this disease. Not all cases of shipping fever are apparent during the journey or immediately after arrival. A substantial number of cases will be not be apparent until the morning after arrival or thereafter.

When the clinical signs of shipping fever are observed during road journeys, veterinary help should be sought immediately or, if not possible, immediately after arrival. During air transport, if there is a veterinarian on board, treatment should begin immediately. It has been shown that prompt intervention significantly reduces the duration of therapy and severity of illness.

Colic and other unpredictable conditions that occur with horses can also occur in transit on the road or in the air. The handling of these conditions should be approached with the same urgency as shipping fever.


  • Carolyn Stull, MS, PhD, of UC Davis is a Cooperative Extension Specialist and lecturer at UC Davis. She has authored numerous articles on the welfare of horses and livestock and was a major contributor to this Horse Report.
  • Anne Rodiek, MS, PhD, has recently retired as a professor in equine studies and has performed research in horse transport, breeding and nutrition for over 30 years.
  • Jim Jones, DVM, MS, PhD, a specialist in equine exercise physiology and sports medicine, has been researching transport stress for many years with colleagues at the Japan Racing Association. His most recent work focuses on heart rate variability as a sensitive indicator of stress in traveling horses.
  • Desmond Leadon, MA, MVB, MSc, FRCVS, RCVS, is head of clinical pathology at the Irish Equine Center and formerly international director of the American Association of Equine Practitioners. He has a long-standing interest in the long-distance transport of horses.
  • Michael Ball, DVM, runs his own practice at Early Winter Equine Medicine & Surgery in Ithaca, N.Y. We thank these individuals for their contributions.
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