Supplementation of selenium to sheep grazing kikuyu or ryegrass : II. Effect on selenium concentration in the grass and body tissues

Abstract

The investigation entailed four trials in which selenium (Se) was supplemented to lambs grazing kikuyu (Pennisetum clandestinum) pastures during two summer periods or Italian ryegrass (Lolium multiflorum) pastures during two winter periods. Two methods of supplementing the lambs were tested, via fertilizing the pasture with Se and/or injecting a long-acting parenteral Se supplement, and compared with the unsupplemented controls. Ryegrass was more effective (P < 0.01) in accumulating Se when fertilized than kikuyu where the response was so low that the lambs could not meet their Se requirements through the supplemented kikuyu. The tissue Se concentrations of the lambs on Se fertilized ryegrass were higher (P < 0.001) than those in the controls, for example hepatic Se concentrations of the two control groups were 124 and 137 ng/g dry matter (DM) compared to 965 and 848 ng Se/g DM in the respective groups consuming the Se fertilized ryegrass. Parenteral supplementation was effective in supplying Se requirements of the lambs. However, lambs that lost weight during the second season on kikuyu had higher (P < 0.01) tissue Se concentrations than the parenterally supplemented groups during the other trials. Selenium tended to accumulate in a non-linear and decreasing rate with an increase in level of Se intake. It was concluded that with the present recommendations Se fertilization of kikuyu cannot be recommended as a method of supplementing Se to the grazing animal.