Coat and skin morphology of hair sheep breeds in an equatorial semi-arid environment

This study aims to address if are there annual changes in the hair coat traits and skin morphology of hair sheep breeds raised in an equatorial semi-arid region? Coat and skin samples were taken from thirty Morada Nova (4 ± 2 years old; red coat; ±SD) and twenty Santa Inês multiparous ewes (5 ± 2 years old; brown and black coat; ±SD) every 3 months over a year. Hair coat traits included thickness (mm), density (number of hairs cm^-2), length (mm), and diameter (mm), plus epidermal and dermal thickness (μm), sweat glands and blood capillaries area (μm cm^-2) were determined. Means of solar irradiance and ambient air temperature were higher between September and December. Annual changes (P < 0.05) in hair density, diameter, length and thickness, as well as the skin blood capillaries and sweat gland area differed between breeds. The modifications on hair coat traits resulted in minor changes on the effective thermal conductivity of the hair coat surface both for Morada Nova and Santa Ines sheep. Nevertheless, it was clearly evident that the overall cutaneous thermal insulation for Morada Nova sheep was lowest in September that was coupled with lower hair density, coat thickness, and higher sweat gland and blood capillary area (P < 0.05). In conclusion, even in an equatorial region, phenotypic acclimatization on morphological traits of cutaneous surface and skin traits can modify the overall thermal insulation of sheep breeds.