Safety and efficacy of two sustained-release intrareticular selenium supplements and the associated placental and colostral transfer of selenium in beef cattle

One hundred fifty Se-deficient, pregnant, crossbred beef cows were assigned to 1 of 4 treatment groups: group A, Se-deficient control; group B, 1 Se bolus at 0 and 119 days; group C, 1 Se bolus at 0 days; and group D, 2 Se pellets at 0 days. The Se bolus is an osmotic pump designed to release 3 mg of Se/d into the reticulorumen. The Se pellets weigh approximately 30 g and contain 10% elemental Se, which is liberated in the reticulorumen. The Se bolus is designed to provide Se supplementation for 120 days and the Se pellets provide supplementation for up to 18 months. Cattle were maintained on Se-deficient pasture or forages prepared from these pastures for the duration of the experiment. Blood samples were collected from cows prior to treatment (time 0) and at 28, 52, 119, and 220 days thereafter and analyzed for blood Se (BSe) concentration. Body weights were recorded at each sampling time. Blood Se concentration of cows from all supplemented groups were significantly (P < 0.01) higher than control values at all sample dates after treatments began. By the end of the 220-day study, treatment group-B cattle had significantly (P < 0.01) higher BSe concentrations than any other group. Body weights of treatment groups fluctuated throughout the study, but did not differ (P > 0.05) between groups. One cow and 6 calves born to cows during the experimental period died. Necropsy of 5 calves provided no evidence linking these deaths to treatments. A difference (P > 0.05) in mortality between groups was not detected. Blood samples were collected from calves prior to suckling, and were analyzed for BSe concentration. Colostrum samples were collected from dams and analyzed for total Se concentration. Additional blood samples were collected from calves 24 to 48 hours after suckling and analyzed for BSe concentration and serum creatine kinase activity. Birth weight, gender, and health were recorded for all calves. Calves from cows in Se-supplemented groups had significantly (P < 0.001) higher BSe concentrations, both before and after suckling, than did controls. Postsuckle BSe concentrations within the groups of calves were not significantly (P > 0.05) different than presuckle BSe concentrations for any of the groups. Selenium concentrations in colostrum from Se-supplemented cows were significantly (P < 0.001) higher than from control cows. A difference (P > 0.05) was not determined in serum creatine kinase activities or birth weights between groups.