Bowers, C. L., Friend, T. H., Grissom, K. K. et al. 1993. Confinement of lambs (Ovis aries) in metabolism stalls increased adrenal function, thyroxine and motivation for movement. Applied Animal Behaviour Science 36, 149-158.

The results of the present study indicate that lambs maintained in metabolism stalls can be physiologically and behaviourally altered [even though they appear to have all of their physical needs met, they have no opportunity for locomotion, grazing, or physical contact with conspecifics]. Such alterations may affect the applicability of certain types of data derived from these lambs compared with lambs in more extensive housing situations. ... Although casual observations of lambs in metabolism stalls may not reveal any outward signs of distress, this study found that restraint in metabolism stall can alter cortisol and T4 release and increase the motivation of lambs to perform locomotor activity.