HEALING OF MUSCLE TRAUMA AFTER INTRAMUSCULAR INJECTION OF ANTIBIOTICSIN SHEEP - CORRELATIONS BETWEEN CLINICAL, MACROSCOPIC AND MICROSCOPICSCORES

The present study aimed to predict the resultant healing from early le sions (found days 3 and 10 post injection) caused by the intramuscular injection of veterinary antibiotic formulations. Nineteen marketed dr ugs were selected in order to screen a wide range of irritation condit ions at the injection site. Nineteen ewes were each injected intramusc ularly with one of the formulations. Each injection was at a different site, 3 and 10 days prior to slaughter. Fourteen of these ewes also r eceived intramuscular injections at two other sites 21 and 32 days pri or to slaughter. The tolerance was monitored by clinical examination o f the injection site and by gross and microscopic pathology. Myodegene ration and fibre necrosis were determined histologically. The clinical scores did not correlate with the other findings, Myodegeneration cor related with the size of the lesion on day 3 post-injection and was no t found thereafter. Although occasionally found alone, it was generall y associated with and surrounded by fibre necrosis. When myodegenerati on was the only lesion, regeneration was complete by day 21 and the fi brosis was minimal or absent. Necrosis at day 10 post-injection correl ated with necrosis at days 3, 21 and 32 post-injection. Fibrosis becam e prominent around the necrotic muscles from day 10 post-injection. He aling from necrosis was slow with, in some instances, encapsulated deb ris still persisting at day 32 post-injection. The tissue irritation i ndex correlated well with myodegeneration and necrose (acute lesions) and fibrose and necrose (older lesions). Thus, after considering a lar ge sample of antibiotic formulations, this study indicated that healin g could be predicted from the muscle fibre histopathology at days 3 an d 10 post-injection. If myodegeneration was found alone, full recovery within 21 days could be predicted. If fibre necrosis was extensive, t he healing involved encapsulating the necrotic tissues and thus result ed in extensive scar formation. The tissue changes explained why the i rritation index of the lesions at days 21 and 32 post-injection could be predicted from their irritation index at days 3 and 10 post-injecti on. Likewise, the size of the lesion at days 21 and 32 post-injection could not be predicted from its size at day 3 post injection.