Abstract:
Holstein cows on a farm in the Humansdorp district, Eastern Cape province, South Africa,
developed reddened, painful teat skin 3 days after grazing a mixed forage crop dominated by
bulb turnip (Brassica rapa, Barkant cultivar). The crop was grazed 45 days after planting and
10% of the herd developed symptoms. More characteristic non-pigmented skin lesions started
manifesting 1–2 days after the appearance of the teat lesions. Affected cows had elevated
serum activities of gamma-glutamyl transferase, glutamate dehydrogenase and aspartate
aminotransferase. These blood chemistry findings confirmed a secondary (hepatogenous)
photosensitivity. As a result of the severity of the teat and skin lesions, seven cows were
slaughtered and tissue samples from five of them were collected for histopathological
examination. Liver lesions in cows that were culled 3 or more weeks after the onset of the
outbreak showed oedematous concentric fibrosis around medium-sized bile ducts and
inflammatory infiltrates in portal tracts. Characteristic lesions associated with other known
hepatobiliary toxicities were not found. No new cases were reported 5 days after the cattle
were removed from the turnips. The sudden introduction of the cows, without any period of
transitioning or adaptation to grazing turnips, as well as the short latent period, clinical signs
of photosensitisation, blood chemistry and histopathology, confirmed a diagnosis of Brassicaassociated
liver disease, a condition seen in New Zealand but not previously described in
South Africa. Brassica forage crops are potentially toxic under certain conditions and farmers
must be aware of these risks.
