SELENIUM SUPPLEMENTS FOR GRAZING SHEEP .4. THE USE OF INTRARUMINAL PELLETS CONTAINING ELEVATED QUANTITIES OF SELENIUM

Possible problems which might arise when using intraruminal pellets containing up to 20% selenium to supplement grazing sheep were examined in two experiments. In Experiment 1, 90 lambs (10 lambs per treatment) were given 1 pellet containing 2-10% selenium or two pellets containing 3-5% selenium. Blood selenium concentration was monitored for 30 months. In Experiment 2, 50 adult sheep were either unsupplemented or given a pellet containing 5, 10, 15 or 20% selenium. Blood and plasma selenium concentrations and liveweight were monitored over approximately a year, and at the end of the experiment wool production and fibre diameter were determined, the sheep were slaughtered and the selenium content of the liver, kidney and the diaphragm muscle were determined. The pellets were recovered at slaughter and were analysed for selenium. Pellet longevity was assessed from blood selenium concentration, and increased with the selenium content of the pellet. Blood selenium concentration was elevated for a shorter period when two pellets containing 3, 4 or 5% selenium were given than when a single pellet containing 6, 8 or 10% selenium was administered. Growth, wool production, fibre diameter and health were not adversely affected by giving pellets containing up to 20% selenium. Selenium concentrations in the diaphragm muscle, liver and kidney were elevated by selenium pellets but did not exceed maximum concentrations laid down by regulatory authorities for products intended for human consumption.