Reasons for performing study: Acorn toxicity has been anecdotally reported to cause fatal colitis and colic in horses but reports in the scientific literature are sparse.

Objectives: This study reports the diagnosis, treatment, prognosis and outcome of 9 cases with suspected acorn toxicity admitted to 2 referral hospitals.

Study design: Retrospective case series.

Methods: Case records from 2004 to 2013 were reviewed. Horses were included in the study if they met 3 of 4 criteria: exposure to acorns; clinical and laboratory data suggesting alimentary or renal dysfunction; acorn husks in the faeces or gastrointestinal tract; and necropsy and histopathological findings consistent with acorn toxicity. Data collected included case history, clinical presentation, clinicopathological data, ultrasonographic findings, case progression, and necropsy and histopathological findings.

Results: Nine horses met the inclusion criteria. Five cases presenting with haemorrhagic diarrhoea deteriorated rapidly and were subjected to euthanasia or died. Four cases showed signs of colic with gas distension, displacement of the large colon and diarrhoea. Three of these (33%) survived with medical management, the fourth was subjected to euthanasia. Post mortem examination of 6 cases demonstrated submucosal oedema of the large intestine and caecum (n = 6), acute tubular nephrosis (n = 6), diffuse necrohaemorrhagic and ulcerative typhlocolitis and enteritis (n = 4), and small intestinal oedema (n = 3).

Conclusions: Acorn ingestion may be associated with typhylocolitis leading to diarrhoea, colic and acute renal tubular nephrosis. Recovery is possible in mildly affected cases; more severe cases show hypovolaemia, intractable pain, renal dysfunction and cardiovascular failure, and often succumb to the disease process. Disease is only seen in a small proportion of the population exposed to acorns and there seems to be an increased occurrence in certain years. Further investigation into factors predisposing to disease is required, but limiting exposure to acorns in the autumn seems prudent.