A review of recent research on the transportation of horses¹

ABSTRACT Horses are transported more frequently than any other type of livestock. Most of our understanding about horse transport has been based on custom and conjecture, but some recent studies have greatly increased our knowledge. Although some horses adapt to transport much better than others, transport is generally associated with lower reproductive rates, increased disease incidence, a temporary reduction in athletic performance, and the alteration of many other physiological traits that are indicative of stress. Horses show marked dehydration after 24 h and extreme dehydration after 28 h of transport in hot and humid conditions when there is little nighttime cooling. Watering horses onboard trailers alleviates dehydration, but fatigue can become extreme after 28 h of transport. Orientation either toward or away or diagonally from the direction of travel does not seem to significantly affect a horse's ability to maintain its balance. Allowing horses the ability to raise and lower their heads or hind quarters and to take at least one step in any direction seems to be the most important factor in their compensating for changes in inertial forces. Loose horses that are transported in groups at high densities (e.g., slaughter horses) do not hold each other up, but rather inhibit each other's attempts to compensate for changes in inertial forces. High density also increases injuries and inhibits the ability of horses to stand after they fall because other horses standover the downed horses. High density also prevents submissive horses from moving away from aggressive horses, resulting in repeated aggression. However, reducing density greatly increases transportation costs. Recent surveys have also shown that many of the worst injuries seen on horses arriving at slaughter plants originated before their transport to slaughter. Horse trailer design has undergone rapid change with the rise in popularity of slant-load aluminum trailers. A major challenge for the future is determining which of the myriad of trailer designs, suspension systems, and building materials available to horse owners and shippers are preferable.

Implications

Horses show extreme dehydration after 28 h of transport in hot and humid conditions. Watering horses on board trailers will alleviate dehydration, but fatigue can become extreme after 28 h of transport. Orientation (facing forward, back, or diagonal) does not seem to significantly affect a horse's ability to maintain its balance. Loose horses that are transported in groups at high densities (e.g., slaughter horses) do not hold each other up, but inhibit each other's attempts to compensate for changes in inertial forces and have increased injuries; the ability of horses to stand once they fall is also inhibited. High density also prevents submissive horses from moving away from aggressive horses, resulting in repeated aggression. Reducing density, however, greatly increases transportation costs. A major challenge is determining which of the myriad of trailer designs, suspension systems, and building materials available are preferable from the standpoint of the horse.

Key Words: Behavior, Horses, Stress, Transport

© 2001, by the American Society of Animal Science. All rights reserved.

J. Anim. Sci. 2001. 79:E32-E40