Evaluation of the cobalt requirement of beef cattle based on vitamin B-12,folate, homocysteine and methylmalonic acid

This investigation was designed to estimate the Co requirement of growing c attle on the basis of plasma and liver levels of vitamin B-12 and folate, p lasma levels of homocysteine and methylmalonic acid (MMA) and haematologica l variables. For this purpose thirty-four male intact cattle of the German Simmental breed (236 kg) were assigned randomly to ten groups and were fed corn silage-based diets which contained 70, 90, 109, 147, 184, 257, 327, 42 1, 589 or 689 mug Co/kg DM for 40 weeks. One-slope broken-line model analys is and a quadratic model with plateau were used to estimate the Co requirem ent. The broken-line model estimated the dietary Co requirement of growing cattle to be 257 (se 29) mug/kg dietary DM based on plasma vitamin B-12 as response criterion. The dietary Co levels needed to maximise the liver vita min B-12 and liver folate were 236 (se 8) and 190 (se 8) mug/kg dietary DM respectively. Plasma folate did not show any response to the different Co l evels. The dietary Co was inversely correlated with the plasma concentratio ns of homocysteine and MMA. Estimates of the dietary Co concentration requi red to minimise homocysteine were 161 (se 10) mug/kg DM. When MMA was used as response criterion, the linear model yielded a Co requirement of 124 (se 3) mug/kg dietary DM. The quadratic model did not provide a better closene ss of regression fit and yielded similar requirements to the linear model. Haemoglobin concentration and haematocrit tended to have a slight response to increasing dietary Co and were only decreased in cattle on diets contain ing less than 100 mug Co/kg DM. On the basis of the present data, recommend ed levels of dietary Co for normal folate metabolism and minimum homocystei ne and MMA levels can be set to be 150-200 mug/kg DM; for maximum vitamin B -12 levels, the desired Co content in the diet seems to be 250 mug/kg DM.