Trace elements, Copper and Selenium in wool production

Copper deficiency

In sheep, the characteristic crimp in the wool becomes less distinct, until the fibres emerge as almost straight, hair-like growths, to which the terms ‘stringy’ and ‘steely’ wool have been applied. The tensile strength of the wool is reduced and the elastic properties are abnormal. A spectacular restoration of the crimp and physical properties can be achieved by copper supplementation.

The abnormalities are most obvious in the wool of merino sheep, which is normally heavily crimped. The crimp is dependant on the presence of disulphide bridges that provide the cross-linkages or bonding of keratin and on the alignment or orientation of the long-fibre fibrillae in the fibre. Both of these are adversely affected in copper deficiency.

Lack of pigment in black-woolled sheep is also a clinical sign of copper deficiency. The pigmentation process in sheep is so sensitive to changes in copper that alternating bands of unpigmented and pigmented wool fibres are produced.

High molybdenum and sulphur intakes further reduce copper absorption and increase the possibility of copper deficiency.

Sheep are however extremely intolerant of excess copper. Chronic copper poisoning has been found in sheep receiving large amounts of copper. Diets/licks/copper supplements containing over 15mg Cu/kg can cause poisoning. Poisoning rarely occurs with grazing sheep under natural conditions.

Selenium

In ewes, high embryonic mortality between 3 and 4 weeks after conception has been attributed to selenium inadequacy in association with white muscle disease and unthriftiness. In certain areas 20 – 50% of ewes were infertile, losses of lambs were high and fertility was dramatically improved by administration of selenium before mating.

Sub clinical manifestations of selenium deficiency in sheep show no distinctive pathological features but have an economically disadvantageous effect.

Selenium supplementation of the ewe increased the probability of lamb survival from 61 – 91%. It also significantly increased lamb weights at birth (4%) and weaning (11%). Wool production may also improve following selenium supplementation. Fleece yields from ewes increased by 3.8-7.5%, and that of their lambs by 9.5%. The mortality of weaned lambs (5 months of age), supplemented with selenium, was reduced from 27 to 8% and highly significant weight gains were observed (1.9kg more).