The effect of length of pastures on cobalt-deficiency disease in lambs

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Abstract
Preliminary investigations in 1951 at the Winton Experimental Farm, Southland, on a soil type classified as Otapiri silt loam showed that cobalt-deficiency disease was much more marked among lambs on one particular paddock in which pasture was long, than on adjacent paddocks where pastures were short. Experiments to compare the effects on cobalt deficiency of long and short pastures, as determined by light and heavy grazing respectively, were made during the next tWO seasons. Interpretation of results was based on evidence from the analyses of pasture and liver samples for cobalt content, weight changes of lambs, and weight responses of lambs to cobalt dosing. It was found that longer pastures could not account fully for the more marked unthriftiness of lambs in the one particular paddock. Nevertheless, short heavily-grazed pastures appeared to reduce the severity of cobalt-deficiency disease among lambs in the one particular paddock, and prevented it entirely in other more mildly cobalt-deficient paddocks. It is considered that increased cobalt intake from soilcontaminated pastures offers the most probable explanation of the protection afforded by heavy grazing. It was estimated that within a range of conditions similar to those of the trials the minimal level of pasture-associated cobalt needed by lambs is about 0.11 p.p.m. Evidence from other farms on Otapiri silt loam coupled with results obtained at the Winton Experimental Farm shows that this soil type can be classified as marginally cobalt-deficient.

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