Cattle (especially mature Angus, Friesian and related breeds such as Murray Greys) can develop a chronic eosinophilic granulomatous inflammation of the skin, kidneys, heart and other organs 3-10 weeks after grazing vetch pastures or forage crops. On average seven percent of the herd can be affected with a mortality rate of 70 percent. The disease is characterised by a pruritic dermatitis of the head, neck, shoulders, tail base, udder and perineum (Harper et al 1993, McKenzie 2012).
We believe this that paper contains the first report of vetch toxicosis in cows fed vetch hay and the first report of vetch toxicosis from common or grain vetch (Vicia sativa subspecies sativa). It occurred when Angus cows were fed Morava vetch hay during the prolonged drought in the Central Tablelands of NSW from 2017 to early 2020. While the morbidity was high, affected cows recovered after vetch hay feeding was stopped and no deaths resulted.
In August 2018 the owner of a herd of about 200 commercial Angus cows from the Bathurst district noticed that 3-4 animals in a mob of 50 first-calf heifers developed red, ulcerated, pruritic skin lesions on the head and neck about 3-4 weeks after commencing feeding vetch hay. The lesions improved rapidly following cessation of feeding the vetch hay but took about three months to resolve completely. In 2018 the vetch hay was obtained from several sources and the variety of vetch is unknown.
In late November 2019 the owner again fed vetch hay commencing at 10 kg/head/day (increasing to 13 kg/head/day) to three mobs of about 50 cows with August- to early September-drop calves at foot. A mob of about 50 yearling heifers were fed a ration of two thirds vetch hay and one third cereal hay. The owner reported that the hay was of high quality, cut from a forage crop of Morava vetch (a variety of common or grain vetch, Vicia sativa subspecies sativa) with a tested protein level of 19.6 percent, metabolisable energy of 11.4 MJ/kg and NDF of 35.2 percent.
In mid-December 2019 the owner noticed red, crusted, pruritic skin lesions on about one third of the first-calf heifer mob. No cows in the other two mobs or the yearling heifers were affected. Several of the calves at foot had skin lesions but when they were examined on 16 January 2020 it was considered that these lesions were consistent with 'ringworm' as they were scant in number, on the heads and necks of the calves and were grey, circular and not pruritic.
The owner stopped feeding the vetch hay in late December and observed that the lesions resolved rapidly within two weeks.
On 17 December 2019 a mob of approximately 50 cows with calves at foot was inspected. There were 6-10 cows with skin lesions involving predominantly the head and neck and occasionally the perineal region. The lesions comprised of large irregular areas of thick crusts that when lifted were erythematous and exudative. Some parts of the lesions only appeared as alopecia and scale. Affected cows were in good body condition and on examination had no other significant clinical signs.
Biopsies were taken from two cows and sent for culture and sensitivity as well as histopathology.
The cattle were again examined in the yards on 17 January 2020. Two previously affected cows had bare areas of normal skin with no evidence of inflammation or pruritis.
Skin scrapings grew a moderate growth of Staphylococcus chromogenes and a saprophytic fungus, both of which were regarded as unlikely to be significant.
In summary, the main findings on histopathology included eosinophilic and histiocytic dermatitis with multinucleate giant cells, including Langhans type. Inflammation was often perivascular and periadnexal and infiltrates sebaceous glands and hair follicles, which occasionally contained necrotic debris. There was also marked ulceration of the epidermis and marked exudation of proteinaceous and necrotic debris.
Multifocally to focally extensively, the epithelium is replaced (ulceration) or overlaid by a thick serocellular crust composed of intact and degenerate eosinophils, nuclear and cellular (necrotic) debris admixed with fibrin, homogenous eosinophilic material (proteinaceous exudate), haemorrhage and refractile debris. In association with ulceration, the epithelium is multifocally thinned and disorganised. The remaining intact epithelium shows one or more of the following changes: orthokeratotic and parakeratotic keratosis, spongiosis, eosinophils traversing epithelium, occasional intracorneal pustules containing eosinophilic and pyknotic cellular debris, and swollen epithelial cells with pale cytoplasm. Within the superficial dermis there is widespread moderate oedema, multifocal mild haemorrhage, multifocal loss of collagen fibre definition and hypereosinophilic staining (collagenolysis). Throughout the dermis there are few to many eosinophils, often perivascularly, surrounding hair follicles and adnexal structures, as well as infiltrating into sebaceous glands and hair follicle luminae, sometimes associated with small foci of eosinophilic and pyknotic nuclear debris (necrosis). Within the dermis, eosinophils are also admixed with fewer macrophages and lymphocytes and there are numerous multinucleate giant cells, including Langhans type. Occasionally, hair shaft luminae are filled with undulating deeply eosinophilic material (suggestive of telogen). There are increased numbers of perivascular lymphocytes and plasma cells, and endothelial cells are multifocally plump (reactive). Apocrine glands are multifocally ectatic.
New varieties of vetch, including Morava, have an increasing role in southern cropping systems. Vetches, especially if grown for hay, provide a valuable option in cereal and canola rotations, fixing nitrogen, enabling control of herbicide-resistant weeds and providing a suitable seedbed for direct drilling the subsequent crop (Grains Research and Development Corporation, Grow Notes, Vetch February 2018). Vetch hay has been shown to be palatable with high protein and reasonable energy levels. It has been popular with southern dairy farmers for two decades and has become increasingly popular with beef cattle and sheep producers during the current drought.
This case is unusual in several respects. This paper is understood to contain the first report of vetch toxicosis from the consumption of vetch hay rather than forage vetch. Secondly the toxicosis occurred following feeding hay made from a crop of Morava vetch, which is a variety of V. sativa ssp. sativa. Previously reported cases have occurred following grazing woolly pod vetch (V. villosa ssp. dasycarpa and eriocarpa), narrow leafed vetch (V. sativa ssp. nigra) and purple or popany vetch (V. benghalensis) (Harper et al, McKenzie 2012). Finally in this case the morbidity rate was high in the one affected mob but no deaths occurred and in the second year affected cattle recovered rapidly following the cessation of feeding the vetch hay.