Plasma vitamin B12 and reproductive performance of cows on cobalt-deficient pastures in the Rift Valley of Kenya.
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Plasma vitamin B12 and glucose in beef and dairy cattle were determined in a well-managed and poorly-managed farm in the cobalt-deficient pastures of the Naivasha area of the Rift Valley of Kenya. These values were compared to those obtained in a well-managed farm from cobalt-replete pastures outside the Rift Valley. Whilst plasma vitamin B12 from the well-managed farm in the Rift Valley (371 +/- 20 pg/ml) were comparable to those from the cobalt-replete pastures (288 +/- 19 pg/ml), those from the poorly-managed farm were significantly lower (156 +/- 13 pg/ml, P less than 0.001). It was noted, however, that even the well-managed farm in the Rift Valley had herd differences indicating how easy it is for the animals to slip into deficiency in the affected pastures. There was no difference in plasma glucose in any of the herds. Fertility, however, was very different. The conception rate at the poorly managed farm was only 30% (with high calf mortality) as compared to 67% in the well-managed farm in the same vicinity. It is suggested that apart from provision of cobalt salt licks, periodic monitoring of plasma vitamin B12 would be a useful safeguard against the onset of unintended, subclinical deficiency.