Open access publications in the SLU publication database

Abstract

This thesis summarises an discusses the results of five separate trials designed to investigate the differences in the availability and retention of supplements of selenium when they were fed to dairy cattle, suckler beef cows and fattening pigs, either in the inorganic form as selenite or selenate, or in the organic form as selenium yeast. The selenium yeast supplement caused a higher concentration of selenium in the blood and the tissues of both cattle and pigs and in cows’ milk than the inorganic selenium supplement. Long-term supplementation of dairy cows and pigs with selenium yeast did not result in toxic accumulations of selenium in their tissues. No differences were observed between the activity of the selenium-dependent enzyme glutathione peroxidase (GSH-Px) in the erythrocytes of cattle or in the whole blood of pigs after they had been supplemented with either inorganic or organic sources of selenium. There was no difference between selenite and selenate as feed supplements for dairy cattle, and both compounds induced only small increases in the concentration of selenium in milk. Suckler beef calves whose dams were supplemented with selenium yeast had a higher selenium status than calves whose dams were supplemented with selenite. The activity of GSH-Px in platelets could be used as an indicator of the short-term selenium status of cattle, but because of problems with the assay it was concluded that at present the concentration of selenium in plasma is a more reliable indicator. Dairy heifers fed an unsupplemented diet had higher plasma levels of the thyroid hormone thyroxine (T4) than heifers supplemented with either inorganic or organic forms ofselenium, but the levels of triiodothyronine (T3) in the two groups were not significantly different, No evidence was obtained for the proposal that selenite might have a pro-oxidative effect in vivo.Selenium yeast can be useful as a feed supplement for suckler cows, in ecological dairying and, when fed to dairy cows and fattening pigs, as a method for increasing the intake of selenium by the human population.