Relationships between integumental characteristics and thermoregulation in South American camelids

Hair fibre is regarded as a unique mammalian feature with an important role for endothermy. Artificial selection for hair characteristics resulted in marked changes with regard to follicle number, type, distribution, growth and natural shedding. This review focuses on the fine fibre-producing South American camelids (SACs) and the relationship between their hair coat and thermoregulation. SACs have developed several special integumental characteristics. While the hair coat of the wild lamoids vicun˜ a (Vicugna vicugna) and guanaco (Lama guanicoe) is formed by two types of hair (the coarse outer guard hairs and a finer undercoat), the domesticated llamas (Lama glama) and alpaca (Lama pacos) exhibit variably double coat and predominantly single coat, respectively. The distribution of the hair coat across the body is not homogenous. Thermal windows with shorter hair or thinner skin can be identified at the ventral abdomen, axillary space and inside of the thighs (about 20% of the skin), thus allowing to modulate heat dissipation. In contrast to sheep wool, lamoid fibres are mainly medullated. The thermal conductance of summer pelage was higher than that of the winter fleece and highest for the axillar and lower flanks. Lamoids have developed behavioural strategies to modify heat loss by adopting specific postures according to ambient conditions by closing or opening the thermal windows. Energy savings of 67% attributed to posture were calculated. SACs have shown to be able to adapt to a broad range of different climatic conditions. The specific integumental characteristics of SACs indicate that they have developed adaptation mechanisms particularly suited for cooler climates. Accordingly, hyperthermia might become a problem in hot, humid areas outside of their original habitat. Several studies showed the beneficial effect of shearing against heat stress. In particular, fertility in males exposed to heat stress may be improved by shearing. Infrared thermography reveals that in shorn animals the heat is radiated across the entire body surface and is not restricted to the thermal windows. However, shearing also changes the conditions of the protective layer, resulting in a loss of thermal conductance that may result in adverse effects when animals are kept under cold temperatures. The length of residual fibre appears to be crucial in avoiding excessive heat loss in a cold environment, as demonstrated by shearing experiments with different shearing machines. There is, therefore, potential for welfare considerations to conflict with industrial demands for fibre length or homogenous quality.