Selenium in Swedish sheep production

Sammanfattning: Selenium (Se) is an essential trace element that is involved in several physiological functions in mammals. Mostly, Se is bound to proteins, many of them with enzymatic functions. A group of seleno-depending enzymes, glutathione peroxidases (GSH-Px’s), are important as antioxidants and protects against free radicals. The activity of GSH-Px is strongly regulated by Se storage in the liver. Deficiency of Se can cause disturbances such as nutritional muscular dystrophy (NMD), lameness, reduced fertility and growth. During pregnancy, Se is efficiently transferred over the placenta and prioritized to the foetus. The bioavailability of Se depends of the origin and inorganic Se in the form of sodium selenite and sodium selenate has lower bioavailability than organic Se in the form of selenium yeast. It is generally known that Swedish soils have low Se contents and for sheep, which mostly have a roughage and pasture based diet, this can cause Se deficiency. In this master thesis, different studies were carried out to investigate the Se status of Swedish sheep and the amount of Se available in feeds. One study contains a set of sheep blood samples taken in 2003-2005 where Se was subsequently quantified. The results suggest that younger ewes have a higher requirement of Se than older ewes. Secondly, a small farm study was performed during the winter 2013/2014 where blood samples were collected at two times, in November and January, from seven ewes. The analyses of Se in whole blood indicate that the ewes’ blood levels were within the reference interval 0.1-0.5 mg/L but at the lower end. Although the Se requirement was met, there was an unexpected decrease in blood Se levels from the first to the second sampling, probably due to a reduced consumption of the mineral feed. Data obtained by Växa Sverige concerning Se content in Swedish roughage are also presented in this thesis and a smaller market survey summarizes the Se content in the most common mineral feeds for sheep that are available at the Swedish market. According to the results found in this study, one can discuss if the daily recommended intake of Se has to be increased and that the age of ewes also should be taken into account, when planning diets and daily allowances of mineral feed.