Clinical efficacy of chlortetracycline hydrochloride administered in milk replacer to calves.

Two similar groups of 14 calves were housed and fed identically in individual pens on a calf-rearing farm. The groups were balanced for weight and immunological status as determined by zinc sulphate turbidity values. When an outbreak of enteric and respiratory disease occurred one group was treated with 20 mg chlortetracycline hydrochloride/kg bodyweight daily for seven consecutive days, by adding the active ingredient to the milk replacer, while the other group was left untreated. Both groups received additional therapy as required. The calves were examined daily during the period of treatment and the clinical observations were assessed and analysed statistically. There was a significant difference between the clinical scores of the two groups on the second day of treatment (P less than 0.05) and on all subsequent days (P less than 0.01) indicating that the calves receiving chlortetracycline hydrochloride were less affected by the disease outbreak. The abnormal enteric and respiratory signs were associated with several potential pathogens including bacteria, viruses and protozoa. The treatment was therefore effective against enteric and respiratory disease involving several organisms.