The application of a selenium fertiliser for the correction of marginal deficiencies in grazing sheep

A commercial fertiliser, consisting of a poorly soluble barium selenate core with a coating of highly soluble sodium selenite, was evaluated in 2 trials for the provision of selenium (Se) to grazing sheep. The fertiliser was administered at a level of 1 kg per hectare to 3 of 6 kikuyu paddocks during 1995 and 1996 in Trial 1, while the other paddocks were left untreated. The Se status of SA mutton merino ram lambs, as reflected by whole blood, liver and kidney Se concentrations, was elevated (P < 0.01) for at least 5 months after application of the fertiliser. Whole blood and liver Se concentrations of animals grazing unfertilised control paddocks were indicative of a subclinical Se deficiency at times (<100 ng Se/ml whole blood and <300 microg Se/kg liver dry matter). In Trial 2, 4 of 7 paddocks on which an oat fodder crop was established were treated with the Se fertiliser during 1995 and 1997. The remaining 3 paddocks were left unfertilised as controls. Groups of 10-15 pregnant SA mutton merino ewes were introduced to these paddocks within 2 weeks of parturition. These ewes and their progeny utilised these paddocks for a mean (+/- SD) period of 41 +/- 8 days after parturition. The whole blood Se concentrations of these ewes and their offspring were elevated (P < 0.01) relative to their contemporaries utilising control paddocks. No suggestion of a subclinical Se deficiency was discernible in animals grazing control paddocks, although whole blood Se levels approached 100 ng Se/ml during 1997. The application of Se fertiliser did not result in improvements in ewe reproduction or lamb growth. There was a suggestion of an improvement (P = 0.21) in mean (+/- SE) lamb survival on paddocks receiving Se fertiliser compared to control paddocks (71.5 +/- 4.6% vs 62.2 +/- 5.3% respectively).