CASE NOTES
A case of inherited alopecia in Poll Dorset sheep
Bruce Watt, Central Tablelands Local Land Services, Bathurst, Beatrice Humphries, student, University of Sydney, Katie Eager, Elizabeth Macarthur Agricultural Institute (EMAI), Menangle, Brendon O'Rourke, EMAI, Imke Tammen, University of Sydney, Leah Johnson, EMAI and Angel Ngo, EMAI
Posted Flock and Herd November 2024
Introduction
Hypotrichosis of unknown genetic cause has been reported in Poll Dorset sheep (Mackie & McIntyre 1992; OMIA:000540-9940). Hypotrichosis in Valle de Belice sheep in Sicily has been reported due to a causal variant in the hairless (HR) gene (Finocchiaro et al. 2023; OMIA:002229-9940) and genetic testing for hypotrichosis has recently been offered in White Suffolk sheep (AWSA, 2021). However, the underlying causal variant has so far not been published.
In this case, five animals sired by a Poll Dorset ram from an unknown ewe flock were confirmed as being homozygous for the markers associated with hypotrichosis in White Suffolk sheep.
History
The owner of a flock of 25-30 ewes of unknown breeding, all joined to a Poll Dorset ram, donated four ram lambs and one two-tooth wether to a near neighbour for disposal. All had pink bare skin, at least on the face, ears and legs. This alopecia was noticed shortly after birth. These lambs were observed to have reduced weight gain compared to the remainder of the lamb drop (of presumably about 20 lambs).
The owner was running a small flock of sheep and backgrounded cattle on mixed ryegrass, phalaris, cocksfoot pasture. There was no known St John's wort (Hypericum perforatum) and the sheep had not grazed crops such as brassicas or cereals.
Clinical findings
Four 6-7-month-old lambs and one two-tooth wether were examined on 10th January 2023. All were in fat score 2 and, apart from their obvious skin and hoof abnormalities, were clinically normal.
Figure 1. The affected sheep with alopecia affecting the face, ears and limbs with pink exposed skin
Sheep 1:
Two-tooth wether weighing approximately 45-50kg with alopecic pink skin over face, neck, legs and ventrum, gradually progressing into thin-woolled skin along the dorsal trunk, with the face most severely affected. The alopecic skin was greasy. The wether had overgrown hooves on the hindlimbs and overgrown dew claws. Rectal temperature was 40.2°C.
Figure 2. Sheep 1, an affected two-tooth wether. Alopecia also extended to the thorax and abdomen in this wether
Figure 3. Sheep 1, skin of forelimb and overgrown dew claw
Sheep 2:
Ram lamb of approximately 20kg, with alopecia over the face and ears, distal hindlimbs and carpus. Skin covering the remainder of its body appeared normal, with normal wool covering. Noted were its overgrown hooves. Rectal temperature was 40.0°C.
Sheep 3:
Ram lamb of approximately 25-30kg. Similarly, skin over the face, ears and forelimbs below the elbow to the feet, and dorsal and lateral hindlimbs was pink and wrinkly, with mild skin ulceration over the hocks. The ram had normal wool coverage and normal underlying skin over the rest of the body. Rectal temperature was 38.2°C.
Sheep 4:
Ewe lamb of approximately 30kg, alopecic pink face and ears, yet the topknot of wool was retained. Completely alopecic skin from the fetlocks down on its hindlimbs and alopecia from the carpi distally on its forelimbs. The dewclaws were overgrown and the rectal temperature was 40.2°C.
Sheep 5:
Ram lamb of approximately 30kg. Alopecic pink wrinkly face and around the horns, but topknot was still present. On the forelimbs, there was alopecia from the carpi distally, and on the hindlimbs, alopecia distally from the hocks on the medial aspects and distally from the fetlocks on the lateral aspect. The dewclaws were overgrown and rectal temperature was 40.8°C.
Laboratory findings
Blood samples from the first three cases (Sheep 1-3) were analysed. Aspartate serum transferase (AST) levels were mildly elevated and blood urea levels were moderately elevated. Zinc levels were within the reference range (from 10.7-15.7 umol/L, reference range 7.0-25) as were copper and vitamin B12 levels. Glutathione peroxidase (GSHPx) levels were low (from 9-32 U/gHb, normal 50-550), a common finding in this district.
Pathology
Histological examination revealed dysplastic changes to the hair follicles in all grossly affected areas of the three sheep. Hair follicles throughout the sections most notably lacked fibres and were instead dilated, often containing abundant keratin (follicular keratosis). Other expected elements of a normal hair follicle (root sheath, infundibulum and bulb) were not present. Sebaceous glands were hyperplastic and hypertrophic. Other findings included orthokeratotic hyperkeratosis and acanthosis of varying severity, as well as mild lymphocytic and/or neutrophilic dermatitis. These histological findings were consistent with those reported by Mackie & McIntyre (1992) in Poll Dorset sheep, and a provisional diagnosis of congenital hypotrichosis was made.
Figure 4. Histopathology of skin (haematoxylin and eosin stain). Hair follicles were often dilated, lacked hair shafts, and sometimes contained keratin. Sebaceous glands were often increased in number and size.
Genetic testing
DNA from the five affected animals was extracted and sent to Neogen (QLD, Australia) for ovine hypotrichosis screening. All five animals were confirmed as being homozygous for the markers associated with hypotrichosis in White Suffolk sheep. It was therefore concluded that the genetic cause in the affected Poll Dorset cross White Suffolk lambs in this study was the same as the so-far-unpublished variant identified in White Suffolks.
Discussion
Various suspected or confirmed genetic forms of hypotrichosis have been reported in livestock and information about these diseases in sheep and cattle are summarised in Table 1 with hyperlinks to relevant entries in Online Mendelian Inheritance in Animals (OMIA, Nicholas et al. 2024). For several of these conditions underlying causal DNA variants have been identified in several different genes.
Table 1: Inherited forms of hypotrichosis in sheep and cattle listed in OMIA
| OMIA ID | Disease | Species | Gene |
|---|---|---|---|
| OMIA:000540-9940 | Hypotrichosis, generic | sheep | Not reported |
| OMIA:000543-9940 | Hypotrichosis, HR-related | sheep | HR |
| Anhidrotic ectodermal dysplasia, EDA-related | cattle | EDA | |
| OMIA:001544-9913 | Hypotrichosis with coat-colour dilution (rat-tail syndrome) | cattle | MC1R, PMEL |
| OMIA:000540-9913 | Hypotrichosis, generic | cattle | Not reported |
| OMIA:002230-9913 | Hypotrichosis, HEPHL1-related | cattle | HEPHL1 |
| OMIA:002114-9913 | Hypotrichosis, KRT71-related | cattle | KRT71 |
| OMIA:000541-9913 | Hypotrichosis, semi | cattle | |
| OMIA:000542-9913 | Hypotrichosis, streaked | cattle | TSR2 |
| OMIA:001949-9913 | Hypotrichosis, with thymic aplasia | cattle | Not reported |
In sheep, zinc deficiency may cause wool loss, thick and wrinkled skin, parakeratosis, reduced growth rate and copious salivation, but was ruled out as serum zinc levels, regarded as a good indicator of zinc status, were normal (Constable et al. 2017).
While the sire was identified as a Poll Dorset, unfortunately it was not possible to examine the ewes that produced these lambs. As all five animals were confirmed as being homozygous for the recessive gene markers associated with hypotrichosis in White Suffolk sheep, it was assumed that at least some members of the ewe flock were also derived from Poll Dorsets or White Suffolks. It is important to note that the Poll Dorset breed contributed to the development of White Suffolk sheep in Australia and it is therefore possible that the causal variant originated in Poll Dorset sheep and was introduced into White Suffolk.
The Anstee Hub for Inherited Diseases in Animals (AHIDA ahida.sydney.edu.au) is a new initiative by researchers and veterinarians at the University of Sydney and the Department of Primary Industry NSW. AHIDA can assist with bringing emerging inherited conditions to the attention of researchers with the aim to develop solutions for industry.
References
- www.whitesuffolk.com.au
- Constable PD, Hinchcliff KW, Done SH and Grunberg W (2017) Veterinary Medicine. A Textbook of the Diseases of Cattle, Horse, Sheep, Pigs and Goats. 11th Edition, Saunders Elsevier, Missouri, pp 1634-7
- Finocchiaro R, Portolano B, Damiani G, Caroli A, Budelli E, Bolla P and Pagnacco G (2003) The hairless (hr) gene is involved in the congenital hypotrichosis of Valle del Belice sheep. Genetics Selection Evolution 35 Supplement 1:S147-56 doi.org PMID: 12927087; PMCID: PMC3231756
- Mackie JT and McIntyre B (1992) Congenital hypotrichosis in Poll Dorset sheep Australian Veterinary Journal Jun 2003 69(6):146-7 doi.org PMID: 1642602
- Nicholas FW, Tammen I & Sydney Informatics Hub (2024) Online Mendelian Inheritance in Animals (OMIA) [dataset] omia.org doi.org