Responses of horses to trailer design, duration, and floor area during commercial transportation to slaughter

Nine trailer loads of horses (n = 306) transported to slaughter facilities with distances ranging 596 to 2,496 km were studied to characterize the typ e of horses used in commercial markets and the physiological responses and number of injuries due to transportation under summer environmental conditi ons. Slaughter horse candidates were middle-aged (11.4 +/- .4 yr), possesse d moderately fleshy body condition, weighed 432 +/- 3.3 kg, and were of Qua rter Horse or Thoroughbred breeding. The mean weight loss during commercial transport was 4%. The percentage of injured horses was greater (P < .05) f or two-tiered "potbelly" (29.2%) compared with straight-deck (8.0%) trailer s; however, the stress indicators of cortisol and neutrophil:lymphocyte rat io and rectal temperature showed greater (P < .05) responses following tran sport in straight-deck trailers. As trip duration increased from 5 h 45 min to 30 h, muscle fatigue (lactate concentration) and dehydration (hematocri t and total protein concentration) were the major physiological considerati ons, especially in durations over 27 h. The percentage of horses injured wa s less (P < .05) in trailers with 1.14 to 1.31 m(2) of floor area per horse than in trailers with 1.40 to 1.54 m(2) of floor area per horse. However, most physiological responses (white blood cell count, total protein concent ration, and neutrophil:lymphocyte ratio) to transportation were less (P < . 05) in horses provided with the greater floor area.