Methods, Thermodynamic Applications, and Habitat Implications of Physical and Spectral Properties of Hair and Haircoats in Cattle

SIMPLE SUMMARY: The physical properties (hair diameter, hair length, haircoat depth, and haircoat density) and spectral properties (solar absorptivity, solar reflectivity, and solar transmissivity) of hair and haircoats play critical roles in heat and moisture exchange between an animal and its surrounding environment. These properties also play an important role in protecting the skin against penetration of ultraviolet radiation. Black haircoats absorb solar radiation, but the absorption occurs at the haircoat–air interface (away from the skin surface) where convective heat loss is high. Holstein cows with dominant black color haircoats are more suitable in latitudes with high solar input than those with a white color haircoat. A white haircoat is more transparent and allows solar energy to penetrate deeply into the haircoat, and thus, heat flows toward the skin surface (heat gain). The physical properties of hair and haircoats are not numerically the same at different locations (dorsal, ventral, lateral, neck, head, etc.) of the body of a cow. The density (no. of hairs/cm(2)) of a haircoat is constant to a certain depth from the skin surface, and then decreases exponentially toward the haircoat–air interface. Cattle with a dominant black haircoat spend more time using shade than those with a white or red haircoat. ABSTRACT: The physical properties (hair diameter, hair length, haircoat depth and haircoat density) and spectral properties (absorptivity, reflectivity, transmissivity) of the hair and haircoat of cattle are inputs to heat and moisture exchange between the skin surface and the surrounding environment, and thus play a critical role in body temperature regulation. Physical and spectral properties of haircoats also play an important role in protecting the skin against penetration of ultraviolet radiation. The focus of this review is to identify accurate and consistent measurement procedures of these properties. Additionally, the paper shows the utilization of the properties on heat exchange models and their implications on voluntary thermoregulation of cattle. To highlight the effects and benefits of haircoat color vis-à-vis solar radiation and its implication on ecological habitation, a brief explanation is provided using polar bears (white haircoat in a cold environment) and black goats in a hot desert environment.