Pasture cobalt concentration and its effect on vitamin B₁₂ status of sheep grazing upland and lowland pastures in the Kaiwera district, eastern Southland, New Zealand

Abstract

Cobalt (Co) concentrations in upland and lowland pastures of the Kaiwera district were monitored for a 13-month period from August 1985 to September 1986 and the effect of changes in pasture Co on the vitamin B₁₂ status of grazing sheep was determined. Co concentration in upland pastures was adequate for stock in winter but fell rapidly to below the critical value of 0.08 ppm Co by lambing time and remained in the range 0.03 – 0.07 ppm for 9 – 10 months until it became adequate again in winter. Co concentration in lowland pastures also fell from adequate values in winter, but more slowly than in upland pastures and was below 0.08 ppm for only 3 – 4 months. The pattern of change in serum vitamin B₁₂ of upland and lowland sheep was similar, as at each site values fell from being highest in spring to a minimum in summer and autumn and then increased again in winter. However, serum vitamin B₁₂ of upland sheep was always at a lower value and in the marginal-deficient range from November through to July. In contrast, lowland sheep had adequate serum vitamin B₁₂ throughout the trial. Liver samples confirmed the low vitamin B₁₂ status of the upland sheep. We conclude that Co deficiency is probable on upland pastures and sheep on these pastures should be given supplementary Co or vitamin B₁₂, or alternatively, they should not be grazed solely on upland pastures for long periods in spring - autumn.

Keywords:

• cobalt deficiency
• vitamin B₁₂
• sheep
• serum
• liver
• pasture cobalt
• seasonal variation