Tolerance and effect of chronic dietary cobalt on sheep.

Degeneration and necrosis of the testes and reduced spermatogenesis were recently observed in rats after prolonged intake of dietary cobalt (Co). The objective of the present study was to evaluate the effect of chronic Co intake on testicular and other tissues in sheep. Adult cross-bred rams were dosed daily for 70 days with gelatin capsules containing either 0, 3.0, or 4.5 mg Co/kg body weight. The Co dosages were increased on days 71 to 109 to 0, 10.0 and 15.0 mg Co/kg. Blood and serum samples were collected weekly and the rams were submitted to necropsy on day 109. Tissues were evaluated for histopathological changes and tissue Co residues and testicular spermatid reserves were determined. Highly significant (P less than 0.005) increases in Co levels were present in the blood, liver, kidney and testes of the treated rams. Neither gross nor microscopic lesions were observed in the testes or other tissues. Spermatid reserves remained unchanged. The absence of lesions and nonsignificant alterations in hematological and biochemical determinations indicated that prolonged exposure to Co at the dosages administered did not induce testicular degeneration in sheep and was tolerated without apparent pathological manifestations.