Physiological responses of mares to short term confinement and social isolation

Abstract

Summary Thirty-six pastured mares, blocked by age and temperament, were assigned to one of three housing treatment groups: pasture (P); confinement stalls (C), allowing social contact; and isolation stalls (ISS), allowing no contact with conspecif- ics. Forty-eight hours post-placement on treatment, the mares were injected intmdermally with a solution of.1 mg phytohe- magglutinin-P (PHA) in .1 ml saline in one side of the neck. After 65 h on treatment, each mare was fitted with a jugular cannula from which a blood sample was drawn and analyzed for plasma concentrations of thyroid hormones and cortisol, complete blood cell counts, and differential leukocyte counts. Blood hemoglobin was elevated for ISS mares, and mean corpuscular hemoglobin content (MCHC) was depressed for ISS mares. Interactions (P .10) in leukocyte counts, but trends were evident. The dermal response to PHA had a treatment by age interaction (P .75 was administered via the jugular cannula. Plasma cortisol concentrations from blood samples drawn 20, 40, 60, 80, 100, 120,150, 180, and 210 min post ACTH administration were then integrated to determine adrenal function (AF). No differences in AF were found (P 4 ) and triiodothyronine (T 3 ), although for C and ISS mares the concentrations of these hormones were higher than the normal values reported in the literature. Concentrations of 3, 3, 5'triiodothyronine (rT 3 ) were higher in ISS mares than in C and P mares. Physiological data suggest that C and ISS mares exhibited evidence of a mild stress reaction with increasing c0nfmement and isolation.