The purpose of this experiment was to investigate the welfare of pregnant mares kept in straight stalls and given only limited exercise, conditions that are similar to those encountered in the pregnant mare urine industry. Sixteen 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 (exercised for one 30 min period every 14 days). The horses were housed in straight (or 'tie') stalls for six months and had ad libitum access to grass hay. Each horse's behaviour was recorded on videotape
once per week for 24 h. The major behaviours were eating hay, standing, and stand-resting (head down 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 stalls. Nine of 16 mares were not observed in
recumbency throughout the whole of the six-month observation period, suggesting that horses with no previous experience in straight stalls may be reluctant to lie down. Thirteen of 16 mares dropped to their knees at least once, probably when they were REM sleeping while standing. There were
no significant differences between the Ex and the NoEx mares in baseline plasma cortisol levels or in cortisol response to ACTH. Following 30 min of exercise, NoEx mares showed an increase in cortisol from 5.0 to 5.4 μg dL−1, whereas Ex mares showed a decrease from 4.6
to 3.6 μg dL−1. The NoEx horses that had been confined for two weeks trotted more (NoEx = 22 [6–38; median and range]% of time; 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]%) and grazed less (NoEx = 0%; Ex = 3 [0–12]%). Confined horses show rebound locomotion — that is, a compensatory increase — when released from confinement, indicating a response to exercise deprivation.