Effect of monensin sodium on histological lesions of naturally occurring bovine paratuberculosis

Of 19 adult cows naturally infected with paratuberculosis, 13 were treated with monensin sodium and six remained untreated. At the beginning of the st udy, the severity of the histological lesions was assessed from biopsy samp les of ileum, liver, mesenteric lymph node and rectal mucosa. From the data acquired it was possible to assign the animals so that the lesions in the two groups were similar (P=0.8323). Monensin was administered in the feed, which contained 147.5 mg/kg, and each treated cow received 450 mg of monens in daily for 120 days. At the end of this period all cows were killed and h istopathological findings in the ileum, Ii; er, mesenteric lymph node and r ectal mucosa were compared with the initial findings. A scoring system show ed that monensin had a beneficial effect in the ileum (P=0.077), liver (P=0 .0322) and rectal mucosa (P=0.0578), but under the conditions of the experi ment no such effect could be demonstrated in mesenteric lymph node (P=03599 ). There appeared to be an overall effect on all tissues taken together (P= 0.1335). The effect of monensin may have been due to both a halting and a r eversal of the pathological process. In all but one of the six untreated co ws, the lesions worsened during the course of the experiment. (C) 2000 Harc ourt Publishers Ltd.