Effects of season and lower ambient temperature on the structure of the sweat glands in anhidrotic horses

Abstract

Histological studies of the sweat glands of anhidrotic horses in the Hong Kong summer and under conditions of reduced thermal stress, both natural and controlled, were undertaken to determine if glandular regeneration occurs. Clinical data were collected for comparison with the histological results in each instance. Horses were assigned to one of three categories on the basis of the resulting change in the number of thin glandular profiles in a cooler environment. Group 1, which was classed as normal, had a low initial value, which was maintained. Group 2, typical of mild and moderately affected animals, had a high initial value, which fell markedly after as little as six weeks in the cool environment. Animals in Group 3, classed as severely affected, had a high initial value which remained high even after prolonged exposure to the cool environment. Light microscopical examination of the sweat glands in the heat, and after six weeks in a cool environment, provided a means of predicting the degree of anhidrotic severity and the potential for recovery in a cool climate. This was superior to clinical observation, although a diagnostic test based on glandular function is still required.

Equine sweating and anhidrosis Part 2: anhidrosis

“…1) can therefore be considered as representative of a gland that has been active for a significant period of time. Over 70% of the secretory cells in the glands of freely sweating horses residing in hot humid summer conditions do in fact show flattened, partially degranulated profiles; 23,27 the glands in this instance seem to adapt to the limited respite from environmental stress.…”

“…Irrespective of the mode of onset, it is clear that anhidrosis is not a uniform condition, there being a variable expression of the magnitude and extent of sweat loss in affected horses as the condition progresses. However, for practical purposes anhidrotic animals are broadly viewed as either mild/moderate/partially anhidrotic or as completely/severely anhidrotic, the former exhibiting some remaining sweating capacity and the latter essentially completely dry 21–23 …”

Atypical histopathological findings in a 15‐year‐old Warmblood gelding diagnosed with anhidrosis in a temperate climate

“…Typical histopathological findings in the skin biopsies of anhidrotic horses include paucity of sweat glands, flattened secretory epithelial cells and thickened basement membrane, all features evident in this horse (Evans and Smith ; Jenkinson et al . ; Bovell et al . ).…”

A review of anhidrosis in horses

“…Thickening of basement membranes is ultrastructurally apparent at this stage and there is some improvement in the sweat gland anatomy of anhidrotics during the cooler months (Jenkinson et al . ). In horses with chronic anhidrosis, basal laminae become irregular and appear thickened even by light microscopy, fundic and ductal epithelial cells are thin, variably degenerate or absent and glands are surrounded by layers of fibrous tissue.…”

“…Depending on the season and chronicity of the condition, 10–50% of excretory ducts are plugged by cellular debris ( Figs and ) (Evans and Smith ; Jenkinson et al . ).…”