Observations on the thrift of young sheep on a marginally Cobalt-Deficient area

Abstract

Weight changes of cobalt-dosed and untreated sheep were compared in seven trials, carried out over a seven-year period at the Wallaceville Animal Research Centre, on land consisting mainly of stonier phases of Heretaunga-Gollans silt loam soils.

Significant weight responses of sheep as lambs were obtained in four out of seven trials (in 1952, 1953, 1954, and 1957, but not in 1951, 1955, and 1956). Sheep responded as two-tooths in two trials but not in another. In the one trial in which it was used, there was a small though significant response to hexoestrol, but no interaction between the effects of hexoestrol and cobalt treatments.

In some years there was considerable unthriftiness and mortality among lambs, irrespective of cobalt treatment. It is considered that a number of factors other than cobalt deficiency, notably internal parasitism, contributed greatly to the unthriftiness and mortality experienced. It was noted that for the years 1953 to 1957 inclusively, during autumn, cobalt-treated lambs at Winton in Southland grew much better than did cobalt-treated lambs at Wallaceville. The years in which lamb growth was poorest were also the years in which no responses to cobalt occurred.

The concept of marginal cobalt deficiency is described. Results of analyses of soils, pastures, and livers for cobalt, and of livers for vitamin B₁₂, are given, and limitations of the diagnostic value of analytical data, with particular reference to marginal deficiency, are discussed.

An important aspect of the present work is considered to be the focusing of attention on the possibility of marginal cobalt deficiency affecting young sheep, over extensive areas of light stony soils related to Heretaunga silt loam, notably in Wairarapa and Canterbury.