Marginal Lack OI Cobalt Thought Widespread

Press, Volume XCVIII, Issue 28920, 13 June 1959, Page 9

Marginal Lack OI Cobalt Thought Widespread

“Marginal” cobalt deficiency exists over large areafc of . Canterbury and possibly over much of the South Island as well. This was stated by Dr. J. W. McLean, head of the veterinary department at Canterbury Agricultural College, Lincoln, in a paper prepared in association with Messrs G. G- Thompson and J. H. Claxton, of his department, which he presented to the farmers’ conference.

Dr. McLean said that significant responses x to cobalt had been obtained this season on the light, shingly soils of the college’s Ashley Dene property and on the medium to heavy cropping land of the Crop Research Division at Lincoln. Whether this was likely to occur every year under varying seasonal conditions they did not, however, know. “From the results /of other workers it seems pretty clear now that this kind of ‘marginal’ cobalt deficiency exists at least over large areas of Canterbury and may be over much of the South Island,” he said. “It sets an upper limit to growth rate in young sheep in some seasons only, and perhaps only on certain types of pasture, and yet is insufficient in degree to produce overt signs of classical cobalt deficiency, except in a small proportion of the flock—that is,the ‘tail-end.’ It would seem to be, therefore, one of the important factors in the overall problem of poor thrift in this area. “Our results this year show fairly clearly that obvious depression of growth does not take place until November or when the lambs have reached about 10 to 12 weeks of age. Whether this critical time is related to the cobalt content of pasture or to the requirement of the growing animal is not clear. Apparently, it is not often required before this, and this may be an important factor in determining the best time to apply cobalt supplements, so that the most effective and economical use may be made of it when it is applied as a spray to the pasture in late spring. “It has been authoritatively stated that such marginal cobalt deficiency cannot be established by chemical analysis qf pasture or liver, and that the only certain way is to observe the response in the growing animal to cobalt supplements. Farmers have, therefore, been recommended to conduct trials of their own with cobalt bullets before applying

remedial measures. While this is an excellent procedure it obviously has certain limitations. It cannot easily be carried out on unweaned lambs and in weaned lambs it takes about two months to find out and in this time , considerable losses may be sustained and responses may be obtained only on certain paddocks and in some seasons. What is the farmer therefore to do? “In the meantime —until more is found out about the nature and extent of seasonal changes in chemical composition of pasture with regard to cobalt—a more practicable procedure would seem to be the application of remedial measures when the condition of young stock, pastures or liver analyses and local knowledge and professional advice suggest that a marginal cobalt deficiency is likely to exist,. If the stock still do not thrive, one possible cause has been eliminated, at little expense, and no harm has been done.'*'

Discussing the position in South Canterbury, Mr M. C. Armstrong, veterinarian of the' Department of Agriculture at Timaru, said that the existence of a seasonal deficiency of cobalt over extensive areas of improved light land had been indicated during the summer of’ 1957-58 by low deficiency levels in livers and by the results of cobalt trials on unthrifty lambs on various pastures and on rape. However, no responses had been obtained in any of the 44 trials which had been started since February on mainly heavier soils. Pasture for the first few weeks had been short and dry but when growth did begin in March and April it was not rapid, long and lush.

Mr Armstrong said that occurrence of incipient cobalt deficiency was undoubtedly induced by the rapid, abundant growth of foliage on leached soils adequately topdressed with lime and phosphate: No molybdenum had been used on these soils but some had been heavily treated with lime at levels of six tons to the acre within six years. No correlation could, however, be established between the severity of ill-thrift and the quantity of lime used during the .previous .six years. More information was required to show what detrimental effects various levels of pH might have on cobalt availability in Canterbury soils. It had been shown in two trials that the presence of a moderate cobalt deficiency could be alleviated by, short pasture or sparse grazing where soil contamination of food occurred. Because soil contained about 30 times as much cobalt as pasture it was considered that ingestion of soil with short or heavily grazed pasture provided sufficient cobalt for lambs under moderate deficiency conditions.

In Ashburton county, Mr K. G. Haughey, senior veterinarian of the Ashburton Veterinary Club, said that 30 trials had been conducted using cobalt drench and bullets. In only three trials—all in the same year—a significant response had been obtained. Two of these properties had, however, experienced severe ill-thrift the following year after topdressing with cobalt. Low liver cobalt levels had been recorded on a number of occasions but cobalt therapy had failed to produce a weight gain on these properties. Recently it had been shown that there was sometimes an interaction between selenium and cobalt and this was now under active investigation. Mr Haughey concluded, however, that cobalt deficiency did not contribute primarily to failure of lambs to thrive in the county.