Multiple cattle with large necrotic skin lesions on sides and/or rump.
Above: Heifer with bilateral necrotising skin lesion extending from caudal shoulder blade to flanks.
Time and location: February to March 2023, Queensland.
Case definition: Necrotic skin lesions on the trunk or rump of young cattle with light-coloured skin, animals 3 years or younger and of either sex. Lesions variable in size and severity.
Disease mapping: A weaner steer with skin necrosis and sloughing over the tail base was seen in 2022. The lesion healed and was suspected to be photosensitisation. An investigation was not pursued as this was the only animal affected. One year later a heifer on the same property had a large eschar extending from the shoulder to flank on both sides, covering a serosanguinous exudate and a bed of granulation tissue. This animal was not seen at the muster in March so is presumed to have died. Another 13 young cattle, 6 months to 3 years of age, were seen with similar lesions over a period of 6 weeks. Affected cattle were from several non-contiguous paddocks on the property. Feed was good due to a good wet season and at the time of the investigation a variety of couch, Seca, Verano and Wynn Cassia were noted. Lantana, crotalaria and coffee Senna were also present throughout the paddocks. All cattle are bred on the property with no introductions except bulls which are typically isolated before joining. At the time of investigation there had been no new introductions to the property for over 12 months. Topical treatments administered include Supona fly spray at the first muster after the wet season.
Gross findings: No significant abnormalities were noted on post-mortem of an affected heifer with pale mucous membranes and mild dehydration. Bloods, fresh and fixed skin samples were collected from the heifer and another two animals.
The differential diagnoses were atypical photosensitisation secondary to lantana toxicity, primary photosensitisation, severe Dermatophilus, other dermatitis or contact dermatitis.
Laboratory findings: A preliminary diagnosis of photosensitisation (primary) was revised to skin necrosis likely due to a topical caustic substance after receiving the photos and a more thorough history.
Animal / management / environment risk factors: Risk factors cannot be described as the cause is not yet established. However cattle with similar lesions were reported on a different property about 500 km away in both 2022 and 2023.
Recommendations: No new cases presented since March and wounds of affected cattle are healing progressively. Should cases recur in the wet season next year, biopsy of early lesions for diagnostic testing is strongly encouraged.