Congenital hypotrichosis in Poll Dorset sheep.

Partial or complete absence of hair has been reported as a congenital defect in all domestic animal species eager and Scott 1985), but thereappear tobefew reports of theconditioninsheep (Lofstedt 1983). This paper reports congenital hypotrichosis and follicular dysplasia in sheep from a Poll Dorset stud flock. In October 1989.2 of about 200 weaners were presented with bald faces, ears and lower legs. Both were ewes about 5 months of age. Eyelashes were absent and there was increased lacrimation Sinus hairs were present on the face. Skin in affected areas was thickened, wrinkled, erythematous and greasy, with mild scaling. The sheep were otherwise in very good condition. The breeder reported that similar cases had occurred over the previous 10 years, at an average rate of one of 80 to 200 lambs annually. Affected lambs were fist noticed at about one month of age, at the time of castration and docking. The lambs' condition at birth was not observed. Afftxted lambs were killed before 12 months of age, with no improvement in their condition. Their health otherwise had remained normal. There was no known access to primary photosensitising agents. Both weaners were necropsied and portions of a variety of tissues, including liver, thyroid and skin from a number of sites were fixed in phosphate buffered 10% formalin and processed routinely for histopathology. Microscopic examination of skin from the facial crest revealed an absence of fibres in follicles, follicular keratosis and sebaceous gland hypertrophy and hyperplasia (Figure 1). There was moderate epidennal hyperplasia with orthokeratotic hyperkeratosis and hypergranulosis. In the stratum basale there were scattered foci of hydropic degeneration and disorganisation of basal cells. In the superficial dermis there was mild dysplasia of collagen fibres and mild cuffing of blood vessels by lymphocytes and macrophages. A section of skin from the facial crest of an unaffected 5-month-old weaner ewe from the same flock is shown in Figure 1. In affected sheep, none of the papillae of follicles that could be identified were intimately associated with follicle bulbs, in contrast to skin from the age-matched unaffected sheep. In skin from the lateral aspect of the hock there was marked dilatation of follicles, with follicular keratosis in addition to the changes described above (Figure 2). Skin from other macroscopically affected areas showed similar histological features to that from the facial crest and hock. In some sections, focal cellular crusts were present on the epidermis with neutrophils accumulating in the superficial dermis and migrating through the epidermis. Sweat glands appeared normal. In skin from wool-covered areas normal wool fibres were present, though some follicles were dilated and keratotic, and there was sebaceous gland hypertrophy and hyperplasia. No gross or histological lesions were apparent in other tissues. Serum was collected from one affected weaner ewe. Gamma glutamyltransferase, glutamate dehydrogenase and aspartate amhotransferase activities and total bilirubin, protein and albumin concentrations were all within this laboratory's reference range.