Effects of “marginal” deficiences of copper and selenium on growth and productivity of sheep

Abstract

Six hundred 6–week–old Romney Marsh ewe lambs were individually allocated at random to one of four treatments and received (a) no treatment; (b) selenium (11.96 mg anhydrous sodium selenate); (c) copper (568 mg CuSO₄.5H₂O); or (d) copper plus selenium (as above), orally, at the commencement of the experiment, and at monthly intervals thereafter until the animals lambed at 2 years of age.

At 11 months of age selenium–treated sheep were 9% heavier and clipped 12% more wool than untreated animals, and at 23 months of age they were 4% heavier and clipped 8% more wool. Fertility, as measured by barrenness in 2–year–old ewes, was unaffected by selenium therapy, but fecundity was significantly improved, the incidence of twinning being 8% higher in selenium–treated ewes.

Significant (p<0.05) copper–selenium interactions occurred, in which live weight, fleece weight, and fecundity responses were induced by copper therapy, but only in selenium–treated sheep. At 11 months of age animals which had received both minerals were 5% heavier and clipped 4% more wool than those which had received only selenium. At 23 months of age they had a 3% live–weight advantage, clipped 6% more wool, and the incidence of twinning was 9% higher.

The greater incidence of twinning among ewes treated with selenium or selenium plus copper was possibly attributable to the improved live weight and hence ovulation rate of treated ewes, rather than being a direct effect on reproductive physiology. Wool growth responses, however, could not be satisfactorily explained on the basis of improved body size alone; they suggested that selenium, and perhaps copper, were involved in physiological processes which could directly affect the rate of wool fibre synthesis.

Clinical symptoms of selenium and copper deficiencies were not seen in either experimental or non–experimental sheep or their progeny during the investigation, nor was the live–weight response to mineral therapy visually discernible, except for a short period before weaning, but the significant production responses were indicative of the economic significance of marginal trace mineral deficiencies in sheep.

Present findings suggest factorial designs should be used in trace mineral studies with grazing animals.