Seasonal influences on quantitative changes in sweat‐associated anatomy in native and thoroughbred horses

Abstract

Stereological techniques were used to assess seasonal influences on morphometric characteristics of hair follicles, sweat and sebaceous glands in abattoir pelts of ponies (PN), thoroughbred (TB) and non-thoroughbred (NTB) horses. Volume density of sweat glands increased significantly from winter (0.061) to summer (0.098) in TB, and showed no change in NTB and a positive tendency in PN. There might be a body surface area : volume effect for sweat gland parameters as PN had smaller values than either TB or NTB, probably attributable to control of heat loss in winter. In summer, the skin remained thick and the volume density of sebaceous glands was increased in NTB, in contrast to TB where both were decreased. It is possible that in summer, sebum has a particular importance in NTB to enhance wicking of sweat through the pelt. TB showed significantly higher volume measurements of sebaceous glands than NTB and PN for winter: sebum has probably a special importance for water-proofing in TB in winter. PN showed no significant seasonal changes in sebaceous glands, but had a thinner summer skin. Winter values for hair follicle volume density between equine groups were similar (TB, NTB 0.066; PN 0.059), as was skin thickness (1.14-1.19 mm). The volume density lowered significantly in summer in TB and NTB. The volume of hair follicles under a unit area of skin surface decreased significantly in TB and nonsignificantly in NTB and PN. The seasonal adaptations of the skin shown here were most pronounced in TB and differed between breeds.

Relationship between saddle pressure measurements and clinical signs of saddle soreness at the withers

“…The breed composition of the 3 groups was a mixture between Warmbloods, Thoroughbreds and light draught horses. One would expect that Thoroughbreds would be more sensitive to pressure because of their slightly thinner skin (1.094 mm) in comparison to non‐Thoroughbred horses (1.271 mm) (Sneddon et al . 2008).…”

“…The breed composition of the 3 groups was a mixture between Warmbloods, Thoroughbreds and light draught horses. One would expect that Thoroughbreds would be more sensitive to pressure because of their slightly thinner skin (1.094 mm) in comparison to non-Thoroughbred horses (1.271 mm) (Sneddon et al 2008). However, despite these differences there was no evidence of any breed-specific tendencies in the tolerated pressure threshold and therefore we presume that these pressure thresholds are applicable for the average riding horse.…”

Heat stress in horses: a literature review

“…In various studies, the heat stress is also recognized as a teratogen (Graham 2005 ; Ouellet et al 2021 ; Barrier et al 2009 ). Adaptation to heat stress changes the sensitivity of the onset of sweating, as well as the number of active sweat glands and its volume (Sawka et al 2001 ; McCutcheon and Geor 2000 ; Sneddon et al 2008 ). It was reported that repeated exercise initiates the onset of sweating at lower body temperature (McCutcheon and Geor 2000 ) and the sweat gland volume in Thoroughbreds was significantly increased during the summer season when compared to the winter season (Sneddon et al 2008 ).…”

“…Adaptation to heat stress changes the sensitivity of the onset of sweating, as well as the number of active sweat glands and its volume (Sawka et al 2001 ; McCutcheon and Geor 2000 ; Sneddon et al 2008 ). It was reported that repeated exercise initiates the onset of sweating at lower body temperature (McCutcheon and Geor 2000 ) and the sweat gland volume in Thoroughbreds was significantly increased during the summer season when compared to the winter season (Sneddon et al 2008 ). Adaptation to the prolonged heat stress can be fixed in gene expressions such as changes in morphological traits, behaviour, metabolism, and productivity over generations to decrease metabolic heat production and increase heat dissipation efficiency (Geor et al 1996 ; Sejian et al 2018 ; Bernabucci et al 2010 ).…”

Physiological response, function of sweat glands, and hair follicle cycling in cattle in response to fescue toxicosis and hair genotype

“…Trends showed thinner epidermis, greater sweat gland density, more follicles in telogen and fewer in anagen, and downregulation of acta2 for the second biopsy taken in July. Greater sweat gland density or volume and decreased skin thickness in summer compared with winter were observed in Thoroughbreds (Sneddon et al, 2008). α-Smooth muscle actin is expressed in hair follicle dermis (Jahoda et al, 1991), the arrector pili muscle (Aneiros-Fernández et al, 2011), and myoepithelial cells of the secretory portion of the sweat gland (Kurata et al, 2014).…”