Physiopathological changes related to the use of ractopamine in swine: Clinical and pathological investigations

The aim of the study was to investigate clinical and pathological modifications induced by treatment with different doses of the β2-agonist ractopamine (RAC) in pigs. Thirty-two eight-month-old Landrace × Large White pigs (mean weight, 102.8 ± 6.7 kg) were treated with 0, 10 (R10), 20 (R20) and 40 (R40) mg/kg/diet of RAC for the last 35 days before slaughtering. Before and after treatment body weight was recorded, blood samples were collected for complete blood count and thyroid hormone concentration analysis, and cardiac instrumental evaluation was performed. At slaughtering, tissue samples were collected for histopathological examination. None of the animals showed any signs of clinical disease during the study period. Treatment did not induce any statistically significant difference in complete blood counts (P > 0.05) among groups. A significant (P < 0.05) decrease in feed consumption was observed between R10 and R40 treated animals. A significant (P < 0.01) increase in ventricular internal dimensions and left ventricular mass was observed in R20; a significant reduction in thyroid weight (P < 0.05) was observed in the animals receiving the highest-dose treatment (R40). Urethral hyperplasia and metaplasia, and prostate hyperplasia and a significant (P < 0.05) reduction in circulating triiodothyronine levels were found in overall treated animals. Taken together, these data suggest that RAC treatment in pigs induces adaptative non-neoplastic urethral and prostatic disorders of growth and a reduction in thyroid hormone concentrations. Nevertheless, additional research on a larger group of animals is needed to define the biomolecular mechanisms underlying the observed lesions, in order to improve the surveillance tools to identify illegal treatments.