Evaluation of the cobalt requirement of beef cattle based on vitamin B12, folate, homocysteine and methylmalonic acid

Abstract

This investigation was designed to estimate the Co requirement of growing cattle on the basis of plasma and liver levels of vitamin B12 and folate, plasma levels of homocysteine and methylmalonic acid (MMA) and haematological 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, 421, 589 or 689 μg Co/kg DM for 40 weeks. One-slope broken-line model analysis and a quadratic model with plateau were used to estimate the Co requirement. The broken-line model estimated the dietary Co requirement of growing cattle to be 257 (SE 29) ΜG/KG DIETARY DM BASED ON PLASMA VITAMIN B12 AS RESPONSE CRITERION. THE DIETARY CO LEVELS NEEDED TO MAXIMISE THE LIVER VITAMIN B12 AND LIVER FOLATE WERE 236 (se 8) and 190 (se 8) μg/kg dietary DM respectively. Plasma folate did not show any response to the different Co levels. The dietary Co was inversely correlated with the plasma concentrations of homocysteine and MMA. Estimates of the dietary Co concentration required to minimise homocysteine were 161 (se 10) μg/kg DM. When MMA was used as response criterion, the linear model yielded a Co requirement of 124 (se 3) μg/kg dietary DM. The quadratic model did not provide a better closeness 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 containing less than 100 μg Co/kg DM. On the basis of the present data, recommended levels of dietary Co for normal folate metabolism and minimum homocysteine and MMA levels can be set to be 150–200 μg/kg DM; for maximum vitamin B12 levels, the desired Co content in the diet seems to be 250 μg/kg DM.