The effect of exercise deprivation on the behaviour and physiology of straight stall confined pregnant mares

The purpose of this experiment was to investigate the welfare of pregnant m ares kept in straight stalls mid given only limited exercise, conditions th at are similar to those encountered in the pregnant mare urine industry. Si xteen pregnant mares (eight in each of two years) were randomly assigned to two groups: Ex (exercised in a paddock for 30 min per day) or NoEx (exerci sed for one 30 min period every 14 days). The horses were housed in straigh t (or 'tie') stalls for six months and had ad libitum access to grass hay. Each hors's behaviour was recorded oil videotape once per week for 24 h. Th e major behaviours were eating hay, standing, and stand-resting (head clown and one hind limb flexed). There was no difference between the behaviours or the number of foot lifts per min of the Ex and NoEx groups in their stal ls. Nine of 16 mares were not observed in recumbency throughout the whole o f the six-month observation period, suggesting that horses with no previous experience BE straight stalls may be reluctant to lie down. Thirteen of 16 mares dropped to their knees at least once, probably when they were REM sl eeping while standing. There were no significant differences between the Ex and the NoEx mares in baseline plasma cortisol levels or in cortisol respo nse to ACTH. Following 30 min of exercise, NoEx mares showed an increase in cortisol from 5.0 to 5.4 mug dL(-1), whereas Ex mares showed a decrease fr om 4.6 to 3.6 mug dL(-1). The NoEx horses that had been confined for two we eks trotted more (NoEx = 22 [6-38; median and range]% of lime, Ex = 2.4 [0- 8.7]%) and galloped more (NoEx = 6 [2-8]%; Ex = 0 [0-4]%) than the Ex that were released daily, but walked less (NoEx = 17 [10-26]%; Ex = 35 [20-40]%) mad grazed less (NoEx = 0%; Ex = 3 [0-12]%). Confined horses show rebound locomotion - that is, a compensatory increase - when released from confinem ent, indicating a response to exercise deprivation.