The safety of dimetridazole alone and in conjunction with oxytetracycline in Hereford crossbred steers

Abstract

Dimetridazole was given intraruminally alone, and in conjunction with oxytetracycline to healthy, 10-11 month-old Hereford cross-bred steers (n = 6). Intraruminal treatment with dimetridazole was given through a fistula at 75 mg kg-¹ daily for 5 d, while the oxytetracycline was injected intramuscularly at 10 mg kg-¹ on Days 1 and 3 of the dimetridazole treatment. The animals were observed at various intervals throughout the trial period for adverse reactions, including effects on ruminal activity and motility, changes in live-mass, venous acid-base balance, haematology and ruminal and serum ammonia concentrations. Dimetridazole, either when used alone or in conjunction with oxytetracycline, had a marked effect on ruminal function. Within 6 h of dosing, the ruminal pH fell to below 5, but then returned to pretreatment values over the next 24-48 h. This was followed by the eradication of the ruminal protozoal population in all animals tested and an increase in the methylene blue reduction time to more than 6 min. Ruminal motility remained unaffected throughout this period. During the week of treatment, the mean live-mass of the animals dropped by 20 ± 9,9 kg in the dimetridazole treated group and by 13,3 ± 2,8 kg in the animals treated with both dimetridazole and oxytetracycline. A mild to severe watery diarrhoea, which continued for 1 to 2 d, occurred in 4 animals after the first dimetridazole treatment. A compensated metabolic acidosis and an increase in haematocrit were observed. An initial transient rapid rise in rumen ammonia concentrations did not result in a concurrent rise in serum ammonia concentrations. Except for one animal, all the others recovered without intervention by the end of the trial period. However, in the one exception, it was necessary to administer fresh rumen content to re-establish ruminal activity. No significant differences were observed between the 2 treatment groups for any of the observations made.