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The present study evaluates blood GSHPx activity in 18 sheep flocks at range, to identify those seasons with the highest risk of selenium deficiency. Samples were taken from 1108 15-day-old lambs during the two usual lambing periods in this geographical area (autumn-winter and spring-summer). The overall mean values in the first period (146.69 +/- 3.41 i.u./g Hb) was higher than in the second one (107.50 +/- 3.53 i.u./g Hb). This may be explained by the special features of the climate in the Mediterranean area, which allow an optimum growth of grass from October to May. Therefore, the lambs born in spring-summer are from pregnancies in months when feeding is based only upon grazing. However, lambs born in autumn-winter comes from ewes gestating during the summer, when supplementation with cereal grains is given. As a conclusion, lambs born in spring-summer in this area are at higher risk to selenium-deficiency related disorders.

This work evaluated the efficacy of barium selenate supplements in the prevention of disorders related to Se deficiency in sheep maintained at pasture in the Mediterranean area. Ewes on five farms were divided into two equal groups of 1,750 animals: a) the treated group and b) the control group. The animals of the treated group were injected subcutaneously, in the first third of gestation, with a barium selenate compound at a dose of 1 mg Se/kg. The ewes in the control group did not receive any supplement of Se and/or vitamin E. The two groups were managed under the same feeding and husbandry practices throughout the experiment. After lambing, blood glutathione peroxidase (GSHPx) and serum aspartate aminotransferase (AST), creatine kinase (CK) and lactate dehydrogenase (LDH) activities were measured in the lambs born to both group. Blood GSHPx activity was higher in the treated animals, with statistically significant differences due to the response to injection of barium selenate. Mean global serum activities of AST and CK tended to be higher in the control group, as a consequence of the protection given to the treated group by the supplement, but the differences were not statistically significant. This was possibly due to the absence of clinical cases of nutritional myodystrophy (NMD) in the animals of the control group. Therefore it can be stated that barium selenate supplementation can prevent Se deficiency in sheep herds maintained at pasture in this area.