The sulfur and selenium status of pregnant ewes grazing Mediterranean pastures

Abstract

Sheep require both sulfur and selenium for normal wool growth and to protect against diseases caused by free radical damage. This work describes the seasonal changes in the concentrations of sulfur, both as glutathione and inorganic sulfur, and selenium, in pregnant ewes, and the effects thereon of a multi-element supplement containing sulfate, selenium, and vitamins A and E.

Merino ewes (420) were divided into 4 equal treatment groups, control (C), vitamins (V), minerals (M), and vitamins plus minerals (V+M), in a 2² factorial design. The control group was offered a loose salt lick NaCl at 175 g/head· day and the mineral group an equivalent amount of a multi-element mineral mix (Siromin). The vitamin groups were offered either salt or the mineral mix with added vitamins E and A. Treatments started 3 weeks prior to mating in November and lasted until 1 week prior to lambing in May. Sheep were sampled until weaning in September.

Regardless of treatment, the concentrations of glutathione in blood and liver declined by 60% and 40%, respectively, when sheep were grazing dry pasture during summer. Sulfate-sulfur concentration in plasma of ewes in the C and V groups declined by 80% in the same period to <10 mg sulfur/L, values indicative of sulfur deficiency. The mineral supplement (M) increased concentrations of plasma sulfate-sulfur at most sample times, but the V+M treatment generally did not. Glutathione concentration in blood and tissues showed little response to supplementary minerals or vitamins.

Selenium concentration in blood of ewes was inversely related to the number of years since receiving a selenium pellet. Mean concentration declined to the deflcient range (0·02 mg/L) in spring in C and V ewes. Treatment with the mineral mix raised blood selenium concentrations to 0·060 mg/L within 2 months and maintained concentrations above the deficient range for several months after cessation of treatment.

The results provide evidence of an under supply of sulfur during the dry summer period and of a need to administer selenium pellets at least twice in the lifetime of ewes.