Objective: To measure responses of cows to supplemental Se intake in excess of nutritional requirements, but lower than recognized toxic dosages.
Animals: 24 healthy adult Holstein cows.
Procedure: Cows were allotted to 4 groups and fed sodium selenite to provide 0, 3, 20, or 50 mg of Se/cow/d for 90 days. Subsequently, the dosage for the group receiving 50 mg/cow/d was increased to 100 mg/cow/d for 28 d. Blood, liver specimens, feces, and urine were obtained at points during the trial.
Results: Serum and blood Se concentrations in groups receiving 20 or 50 mg/cow/d increased over time, compared with controls (P < 0.01). Increasing supplemental Se intake to 100 mg/cow/d further increased serum and blood Se concentrations (P < 0.05). Urine, fecal, and liver Se concentrations increased more markedly in response to treatment than did those of serum or blood. No effect of Se treatment was seen on blood cell counts or serum activities of hepatocellular enzymes. Likewise, neither titer response to rabies vaccination nor lymphocyte blastogenic response to nonspecific mitogens was affected by Se treatment. Objective or subjective physical signs of Se toxicosis were not observed at any Se dosage.
Conclusions: Inorganic Se intakes of up to 50 mg/d for 90 days or 100 mg/d for 28 days by adult Holstein cows do not affect the variables measured.
Clinical relevance: Intakes of Se as sodium selenite in amounts 10 to 30 times the nutritional requirements are unlikely to cause health problems in adult cows. Urine and feces are good test samples for detection of Se supplementation greater than requirements.