The effects of injectable sodium selenite on immune function and milk production in Sardinian sheep receiving adequate dietary selenium.

The aim of this preliminary study was to determine the effects of selenium (Se) injection on Se status, cell-mediated immunity (CMI), milk yield and milk somatic cell count (MSCC) of ewes fed adequate amounts of Se, and on Se status, passive immunization and CMI of their offspring. Thirty days before lambing, 36 Sardinian ewes were assigned to one of three groups. One group (NT) was not treated; a second group (BL) was given 5 mg of Se on day 30 before lambing; a third group (BLL) was given 2.5 mg of Se on day 30 before lambing and at lambing. Selenium was given intramuscularly as sodium selenite. Selenium status was assessed by measuring glutathione peroxidase activity of erythrocytes (GSHpx-E). The CMI was measured by determining the increases in double skinfold thickness after intradermal injection of phytohaemagglutinin (PHA). Compared to their NT counterparts, ewes belonging to BL and BLL groups and their offspring had significantly higher GSHpx-E (P < 0.01). The GSHpx-E values of lambs were positively related to those of their mothers (P < 0.0005). Ewes of group BL had a greater (P < 0.01) response to PHA 6 h after injection than ewes of the NT group. Lambs born to BL and BLL ewes had a greater (P < 0.0001) response to PHA 24 h after injection. Responses of ewes and lambs to PHA 24 h after injection were positively related (P < 0.05). Serum immunoglobulin at 10 days of age did not differ significantly among the three groups of lambs. Compared to the NT group, milk yield on day 70 of lactation was significantly higher in BL ewes (P < 0.05). The MSCC was not affected significantly by Se injection. Immunoresponsiveness and milk yield might represent additional and appropriate criteria to consider when re-evaluating Se requirements of dairy sheep.