A three month old Red Angus calf presented for recumbency and inappetance of 1-2 days. The calf had been acquired five weeks previously as a twin that had been rejected by her mother. During this time, the owner had noticed a decreased appetite and had observed the calf to often be leaning onto the fences and poles. In the past two days, the calf had deteriorated rapidly and on examination was laterally recumbent, depressed, with strabismus and nystagmus.
A complete blood count and biochemistry profile showed non-specific changes. The calf responded to hospitalised supportive care (intravenous fluids, nutritional support) and was able to stand and feed on her own after 24 hours. It was at this time that further neurological signs were observed: head pressing, circling, inco-ordinated gait, proprioceptive deficits, ataxia, and seizures which progressively worsened over the next 24 hours. The calf died soon after despite antibiotic, anti-inflammatory and anti-seizure therapy.
There is mild generalised swelling of the brain identifiable as flattening of the cortical gyri and no other significant gross findings. On histopathology, there is marked diffuse vacuolation of the grey and white matter of the brain. No significant microscopic changes were seen in the kidney, liver, or small intestine.
The histopathological findings in the central nervous system (CNS) of this animal are suggestive of widespread brain oedema, as would be expected in a neurotoxicity that has compromised fluid regulation in the higher CNS. Given the lack of history of an exogenous toxin and the unremarkable changes in the liver and kidney sections, the most likely cause in this case is an endogenous neurotoxin. In such a young calf, this is likely suggestive of an inherited inborn error of metabolism.
The clinical course and diffuse location of the lesions of this animal is not consistent with either of the two well known inherited inborn errors of metabolism in Australian calves: Citrullinaemia in Friesians involving grey matter astrocytic oedema (Harper et al 1986; Healy et al 1990), and Maple Syrup Urine Disease (MSUD) in Herefords and Poll Shorthorns involving white matter intramyelinic oedema (Harper et al, 1989; Healy et al, 1991).
However, there is a report of 'diffuse congenital brain oedema' described in nine horned Hereford calves in New Zealand (Jolly, 1974) in which the described calves had histopathological findings consistent with generalised status spongiosis of both grey and white matter due to severe hydropic swelling of astrocytes and oedema and an overall severe deficiency of myelin.
The precise pathogenesis was not investigated, however the author suggested that the affected calves were an example of a previously unrecorded inherited disease, probably mediated by an autosomal recessive gene, due to the pathological findings, congenital nature of the condition, and the inbreeding practised in the affected herd.
Sporadic cases of this pattern of diffuse brain oedema of neonatal calves that resemble Canavan's disease have been observed on occasions in Australia in a number of breeds with similarities in the lesions noted between the affected calves and Canavan's disease, or spongy degeneration of the children. This is an infantile neurodegenerative disease that is due to aspartoacylase deficiency (Matalan et al, 1998). We would be keen to hear of similar cases as a series needs to be assembled to justify further exploration of this potential animal model of human of yet another human error of metabolism.