Transport Stress in Horses

All horses are stressed by travel, especially if it involves a long time in transport, but some are stressed more than others. The circumstances of shipping may make a difference in the level of stress.

 

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Credit: Tyler Stockton
Stress is defined as the sum of adverse effects on the animal from detrimental factors in the environment or management system which force changes in the horse’s physiology or behavior to assist in coping with those factors.

 

Many things contribute to stress when horses are transported, such as discomfort in a particular van or trailer, motion or noise, road conditions, confinement and available space, footing/balance issues, withholding feed and/or water, temperature and humidity, etc. Thermal comfort (avoiding extreme cold or heat) is important when transporting horses — making sure the environment within the van, trailer or airplane is within the animal’s comfort zone (30 to 75 degrees in still air, with some variability above or below these parameters, depending on wind and humidity). There are also psychological stresses such as separation from herd mates, exposure to new environments or interactions with unfamiliar horses.

Stress lowers a horse’s resistance to disease. Horses stressed by transport are more vulnerable to pneumonia, diarrhea, colic, or laminitis. The latter may be a sequel to standing for long periods without moving. Research has shown that respiratory disease is a common sequel to transport, but until recent years few studies had been done to examine the effects of long-distance transport.

Dr. Carolyn Stull (University of California-Davis) and Dr. Anne Rodiek (California State University-Fresno) worked on several research projects a few years ago, one of which was to study the physiology of horses during 24 hours of transport and during the 24 hours of recovery after transport.

A commercial equine van traveling in summer conditions in central California was utilized for the study. Fifteen mature, healthy horses were chosen--all experienced travelers. The horses’ physiological responses during travel and during recovery (resting in individual stalls) were documented, to see how quickly the horses returned to normal.  Body weight, rectal temperature, white blood count, hydration and other factors were measured. In general, the horses lost about 6 percent of their body weight during transit, due to sweat loss and decreased gut fill (eating less than normal), but they all recovered half of this weight loss during the 24 hour rest period after transit.

Hematocrit and total protein concentrations increased during transit, which is an indication of dehydration, but these measurements returned to normal during the 24 hour recovery period. The horses experienced minimal muscle fatigue (as measured by the levels of lactate in the muscles), but CPK and AST were slightly elevated after transport.  These two serum enzymes are involved in skeletal muscle activity.

Stress levels can be also be measured by looking at cortisol levels in the blood.  This hormone (produced by the adrenal glands) is generally a good indicator of stress. The concentration of cortisol in the 15 horses increased during loading into the transport van and continued to rise during the 24 hour travel, peaking at the end of the trip.  After the horses were unloaded, cortisol levels dramatically dropped.

Since cortisol hinders the immune system, its influence can be measured by the ratio of two types of white blood cells (neutrophils and lymphocytes) that are instrumental in fighting disease. This ratio in the study horses increased during transit and did not return to normal by the end of the 24 hour rest period. The fact it takes longer than this to recover from the effects of stress may be one reason why horses are susceptible to illness following long transport.

Another study conducted by Stull and Rodiek examined the stress level of horses traveling loose in individual box stalls (in a van/trailer or stock trailer), compared with horses traveling tied or cross-tied. Tied horses had larger increases in stress parameters than horses traveling loose. Finding ways to reduce stress can be helpful, especially if your horse arrives at its destination less stressed, ready to compete, and less susceptible to respiratory infection following transport.

Heather Smith Thomas has raised and trained horses for 50 years and has been writing about them nearly that long, selling more than 9000 stories and articles and publishing 20 books. She and her husband raise beef cattle and horses on their ranch near Salmon, Idaho.