Pigmented Spots in the WoolBearing Skin of White Merino Sheep Induced by Ultraviolet Light

Abstract

Black-grey pigmented skin spots, some of which contained pigmented wool fibres, were observed in a flock of 8· 5-year-old white Merino ewes. The spots were concentrated along the backline and increased in number following shearing, suggesting exposure to sunlight to be of importance in the development of these non-congenital pigmented skin spots in genetically white Merino sheep. To test the effect of ultraviolet light, white Merino sheep, ranging in age from 3 to 8 years, had a closely clipped mid side area of wool-bearing skin irradiated on each of 28 consecutive days. Pigmented skin spots developed in 6 of the 16 white Merino sheep irradiated. Spots first appeared after 10 days of irradiation, the number subsequently increasing with time, and two skin spots were found to contain sparse numbers of blackgrey pigmented wool fibres. Histological examination showed both the naturally occurring and irradiationinduced pigmented skin spots resulted from an increase in both number and activity of melanocytes localized along the epidermal-dermal border of the epidermis. With time, the melanocytes were observed to have entered, to varying depths, the outer-root sheath of follicles still producing white wool fibres. These ultraviolet-light-induced changes to epidermal melanocytes in white Merino sheep presumably occur due to alterations within the local tissue environment in which the melanocytes lie.

Assessment of Poisson, Probit and linear models for genetic analysis of presence and number of black spots in Corriedale sheep

“…Fleet (2006) showed that twice yearly shearing increased the development of pigmented spots after 2 years of treatment. This result, with the agerelated trends observed here, is consistent with the idea that exposure of the skin to ultraviolet light (e.g., following shearing) increases the risk of developing black spots in the fleece area (Forrest & Fleet 1986).…”

Estrogen Depletion Results in Nanoscale Morphology Changes in Dermal Collagen

“…Ovine dermis is considerably thicker than human dermis;(Dellmann and Eurell, 1998) in addition a layer of wool equivalent of SPF 30 protection also makes it difficult to assess how much photoageing is induced in these dermal tissue samples as compared with human samples. (Fleet, 2006; Forrest and Fleet, 1986) However given that the Sham and OVX ovine were provided with the same sheltering condition, the effects observed in this study signify change in the hormonal level rather than differential UV radiation exposure.…”

A comparison between Poisson and zero-inflated Poisson regression models with an application to number of black spots in Corriedale sheep

“…A series of environmental and genetic factors may be related to the number of spots. Simple observation (even in humans) suggests that this number increases with age and environmental stress factors (e.g., solar irradiation can be invoked as causative agents [7,8,14,23]). Variability in the underlying genetic mechanisms responsible for the spots is likely, at least in different races, as well as in susceptibility to environmental stress factors.…”