Relationships between integumental characteristics and thermoregulation in South American camelids

Abstract

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 vicuñ 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.

Fundamental hair follicle biology and fine fibre production in animals

“…reptilian) to endothermic (e.g. mammalian) systems of regulating body temperature (Gerken, 2010). There has thus been interest in genomic comparisons across a range of species.…”

“…Figure 7)? Other papers in the symposium have described the presence or absence of hair follicles in different areas of the skin (Gerken, 2010) and important roles in physiology of thermal regulation. The numbers, types and activities of hair follicles and physical characteristics of fibres in different genotypes of South American Camelids have been described (Antonini, 2010).…”

“…Consequently, much of the following information is derived from studies on small animals and particularly genetically modified mice. Such studies have particularly illuminated developmental regulation prenatally although they have contributed less in describing Figure 7 Images of phenotypic expression of hair follicle characteristics at levels of: 1, whole animal (Llama) afollicular and follicular skin (with variation in hair fibre pigment) according to anatomical site (Gerken, 2010); 2, bundles of primary and secondary follicles in histological horizontal skin section of Q'aras llama (Sacpic staining (Antonini, 2010)); 3, vertical section of a cashmere follicle (Toluidine blue; 3128 magnification; Lee and Galbraith (unpublished).…”

“…Although regulation of follicular initiation and growth is important, interest remains in the properties of afollicular epidermis such as described by Gerken (2010) or epidermis with variable concentrations of hair follicles such as described for South American camelids by Antonini (2010) (Figure 7). Current information suggests that hair follicle development is inhibited unless constitutively expressed placode inhibitors such as bone morphogenic proteins (BMPs) 2 and 4, or Activin bA are adequately suppressed by Noggin or Follistatin, respectively (Schmidt-Ullrich and Paus, 2005).…”

“…The contribution of the hair coat to environmental protection and behavioural display of animals is well recognised -E-mail: h.galbraith@abdn.ac.uk (Gerken, 2010). Important properties of hair include thermal insulation and visual appearance, which affect the value of fibre harvested for use by human commerce.…”