Effect of selenium vitamin E supplement on the performance of sheep in Central Iran

Selenium (Se) is an essential trace element in animal nutrition involved in the defense against the toxicity of reactive oxygen species and the oxidation state of cells, where its deprivation reduces activities of the Se-dependent enzymes. The signs in animals depend upon vitamin E status and appear only when both nutrients are limiting where they vary according to species. Estimating actual selenium intake is often difficult due to the specific housing and feeding conditions of sheep husbandry, which is mostly in extensive system in most part of the world and in Iran as well. Indirect indices such as Se concentration in blood, glutathione peroxidase activity and production are used to evaluate Se status. Correct levels of selenium supplementation at different growth stages of sheep are essential to maximize productivity, but few studies have been conducted to determine the composition of mineral supplements for sheep in Iran. This study was designed to monitor the health status of sheep grazing in a dry land zone and to test the response of ewes to selenium vitamin E injection. Three flocks each with 120 sheep, representative as sheep husbandry system of a district zone in Markazi province in central Iran, were considered. Sheep keeping in this area is mostly based on the extensive system depends on poor rangeland, crop residues and stubbles with supplement feeding of barley grain during cool winter when the ewes are at late stage of pregnancy. In each of the selected flock, 60 ewes were identified and divided in two groups including 1) control and 2) treatment, where the ewes in treatment group received selenium-vitamin E (each dose contained 0.5 mg sodium selenate and 50 mg vitamin E) supplement by subcutaneous injections. Each ewe injected by one dose of the supplement 2 weeks before mating and again 2 weeks before lambing. Blood samples were collected, one month post injection that was occurrence to autumn and spring seasons, and analysed for glutathione peroxidase activity (GSH-px). The reproductive parameters were recorded and lamb body weight measured at birth day and weaning time as well. Results of the enzyme activity showed that the treatment had significant effect on the GSH-px at different seasons for flock I and II where the injection of Se-vitamin E increased the enzyme activity comparing to the control but no significant differences were found between the control and treatment in flock II. There were also significant variations of GSH-px among the flocks where the highest amount was found in flock III and the lowest amount in flock I. It may be a realistic explanation that no response was found in flock III as a result of injection. This finding may be indicated the probability of selenium deficiency in the flock and correction of deficiencies by supplementation. These results support the finding of other workers where they reported an increase in erythrocyte glutathione peroxidase activity (139.5 vs. 86.3 U/ml) in dairy ewes by subcutaneous injection of vitamin E and Se. Furthermore supplementation had positive effects on the reproductive performance in all flocks where the lambing rate and final lambs obtained per 100 sheep significantly (P < 0.05) increased in the treatment ewes than the control (Table II). However no differences were found between the treatment and control for the live weight of lambs at birth or weaning times. There was a positive relation between glutathione peroxidase activity and reproductive performance in ewes. It is suggested that reduced fertility and increased mortality of lambs may be related to congenital muscular dystrophy, arising from Se deficiency. (author)