POLIOENCEPHALOMALACIA ASSOCIATED WITH THE INGESTION OF AMMONIUM-SULFATE BY SHEEP AND CATTLE

In the latter part of 1991 an unusual neurological disease was recogni sed on several farms in England. This report describes the case histor ies and clinical, biochemical and pathological findings in six calves and two lambs aged from two to 44 weeks obtained from five of these fa rms. Laminar cerebrocortical necrosis and severe bilateral necrosis of the thalamus and/or striatum progressing to cavitation were recognise d in their brains. These changes are similar to those of experimental sulphate toxicity. Morbidity rates of 16 to 48 per cent and mortality rates of 0 to 8 per cent were recorded. The affected animals did not r espond to vitamin B1 treatment; the erythrocyte transketolase levels o f in-contact cattle and of one untreated affected calf and one untreat ed lamb were within the normal range. All rive farms had recently intr oduced a proprietary concentrate ration containing ammonium sulphate r ather than the normal urinary acidifier ammonium bicarbonate. After th is ration was withdrawn no new cases of nervous clinical disease were observed. It is suggested that, in at least some cases, the morphology and topography of lesions may distinguish sulphate induced polioencep halomalacia from that of sporadic thiamine-dependent cerebrocortical n ecrosis.