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Even if your horse climbs willingly into the trailer each weekend and seems to travel well, he is undergoing some stress each time he’s transported. That is the conclusion of a number of studies showing physiological signs of stress (elevated heart rate, increased cortisol production) in trailered horses that are used to being handled and transported. It can be inferred that reactions would be more pronounced in horses less accustomed to transport. By being aware of travel stressors and taking steps to minimize their impact, owners may be able to help their horses arrive in good condition after transport for various distances in a range of climatic conditions.

General stress Transported horses can theoretically be stressed by separation from herd-mates, close proximity to aggressive horses, unknown surroundings, restraint of normal movement, maintenance of abnormal posture, unfamiliar noises, changes in temperature, feed and water deprivation, and exposure to pathogens, dust, and blowing debris.

Injury Physical injuries to transported horses can be caused by vehicle collisions, sudden stops, falls, loss of balance, collapse due to fatigue, and attacks by aggressive animals. While horses may sustain injuries during transport, studies have shown that the majority of severe injuries observed among horses transported for slaughter were incurred before the horses were loaded onto the transport vehicle.

Fatigue The stress and muscular fatigue associated with transport are similar to, although somewhat different from, those resulting from exercise. It is suggested that competition or performance not be attempted less than 48 hours after extended transport in order for blood levels of hormones and chemicals to normalize. Trips of up to 90 kilometers (about 50 miles) usually have no significant effect on blood profiles or the ability to exercise, while trips of 900 kilometers (540 miles) or more should ideally be followed by several days of rest before horses are asked for strenuous exercise efforts. In one study, healthy horses showed significant signs of fatigue (closing eyes, lowered heads, less social interaction, decreased response to stimuli) after 24 hours of travel. This study was terminated at 33 hours because of greatly reduced responsiveness.

Dehydration Two similar studies measured dehydration of horses transported in small trailers for 24 hours. When the outside temperature averaged 27.3º C. (81º F.), horses lost more than twice as much weight from dehydration than when outside temperature averaged 21.5 º C. (70º F.). Dehydration can be moderated by offering water periodically during transport, although horses may repeatedly refuse to drink. Dehydrated horses may sometimes drink to excess, resulting in colic if they are given unlimited access to water. One study showed that giving severely dehydrated horses 12 liters (3.17 gallons) of water at 30-minute intervals led to colic signs, while in another study moderately dehydrated horses safely drank 14 liters (3.7 gallons) of water at 30-minute intervals. There are no published guidelines for rehydrating severely dehydrated horses. These horses should be carefully observed for signs of distress while they are being rehydrated and should not immediately be given free access to water after a long period of transport.

Orientation in trailer About 25 years ago it was hypothesized that horses might travel most comfortably and keep their balance most easily when their bodies were oriented backwards to the direction of travel. Many studies have since been conducted on orientation preference, with somewhat inconsistent results. Results showed that some horses prefer to face forward, others prefer to face backward, and still others showed a liking for a position diagonal to the direction of travel. Some horses showed a strong preference for facing a window or light area, such as the open area above the rear doors. Heart rates showed little conclusive evidence that one position was less stressful than another. Horses facing backward tended to slip somewhat more than horses in other orientations, but there was no clear relation between orientation and balance, leg moving, or bumping/leaning on barriers. Transporting with or without shoes made no significant difference in horses’ ability to remain standing.

Trailer design Tying horses with their heads above a solid barrier such as a saddle compartment limits their ability to lower their heads at will, possibly adding to fatigue and compromising normal drainage from the nasal passages. Slant-load trailers tend to have somewhat longer stalls, giving horses more room to move around, and their placement of windows alleviates the reluctance of some horses to enter dark or poorly lit spaces. Although horses usually have little trouble maintaining their footing even when road surfaces are extremely rough, trailer suspension has an effect on fatigue during long trips. Leaf-spring suspension with low-pressure radial tires created the smoothest ride in trials, while torsion-bar suspension with normal-pressure radial tires was among the roughest. An air suspension system was not tested but is thought to give an extremely smooth ride.

Density When groups of horses are transported in large trucks, common sense would seem to indicate they would ride most safely when they are packed closely together and able to lean on each other. In fact, moderate density leads to fewer falls and injuries. Horses that are closely packed can’t usually move their feet without stepping on each other, and they are sometimes repeatedly injured by an aggressive horse from which they can’t escape. Other horses may be injured in the scuffle and flight attempts. A horse that does fall down can’t usually rise because the other horses shift into the empty space, trampling the fallen animal. Also, close proximity to other horses increases heat stress in hot weather.

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