Advantages of rebreathing
- J Baum
A ostrich producer ordered tylosin premix in order to treat respiratory disease in his ostrich flocks. Upon receipt of the product it was mixed into the feed at 500 ppm. Six days after commencement of feeding the medicated ration, 1 bird was observed to be lame (remained sitting). By day 7, 5 birds were lame; by day 8, 8 birds were lame and 1 bird had died; by day 9, 30 birds were lame, and mortality was increasing. At this time a veterinarian discovered that the farmer had, due to a clerical error, been supplied with monensin instead of tylosin, and the ration was withdrawn and replaced with a non-medicated ration. Mortality continued to day 14, with the following losses: 1 adult bird (aged 3–4 years), 6 birds aged 14 months, 2 birds aged 12 months, 22 birds aged 9–10 months, 15 birds aged 7–8 months and 3 birds aged 5 months, a total of 49 birds. All the affected birds developed lameness and ataxia, and died. Post mortem lesions were severe reddening of the duodenal mucosa with thick mucous content, liver congestion and sparse myocardial petechiae. No obvious lesions were observed in other organs. Stomach contents contained traces of monensin. Histopathological examination revealed severe multifocal hyaline degeneration and necrosis of the intercostal muscle, mild multifocal atrophy of the myocardium, and mild diffuse liver degeneration. These lesions are evidently compatible with ionophore toxicity, and conform to those previously described. When young (3-month-old) ostriches were fed monensin at 100 ppm no mortality occurred (Allwright, pers. comm.), but susceptibility appears to be age-related. In the light of the above experience, it is recommended that all containers of monensin should carry a warning against use in ostriches, as is already the case in equines.