Amino acid changes in plasma and liver of cobalt-deficient cattle

This study was conducted to investigate the interrelations between cobalami n metabolism and amino acids in cattle fed on a cobalt-deprived diet. Cobal t deficiency was induced in cattle by feeding two groups of animals either a basal corn silage-based diet that was moderately low in cobalt (83 mu g C o/kg), or the same diet supplemented with cobalt to a level of 200 mu g, fo r 43 weeks and the deficiency was obvious by a loss of appetite, diminshed growth gain and declined vitamin B-12 status in serum and liver. Cobalt def iciency in cattle which was primarily a combination of reduced feed intake and a tissue vitamin B-12 deficiency did not affect the concentrations of t otal protein and albumin in serum, nor was there any quantitative change in serum creatinine and hepatic ammonia. However, the cobalt deficiency promo ted an accumulation of significantly more urea in serum than cobalt adequac y, while the activities of transaminases declined. Cobalt deficiency induce d a significant number of changes in plasma amino acid concentrations. Catt le deprived of cobalt experienced a 53% reduction of methionine concentrati on in blood plasma relative to their controls, and the analysis of other es sential amino acids also demonstrated significantly reduced plasma concentr ations of valine, leucine, isoleucine and threonine. The plasma of cobalt-d eficient cattle was also characterized by significant changes in non-essent ial amino acids. These were reductions of the arginine and thyrosine levels and also of the taurine concentration. The most marked changes occurred wi th plasma serine and homocysteine. The cobalt-deprived cattle developed 2.7 -fold higher serine concentrations and 4.8-fold higher homocysteine levels in blood plasma than their controls. In contrast, the amino acid concentrat ions in the liver remained largely unaffected by cobalt deficiency. There w ere only slight increases in lysine, glutamic acid and serine concentration s. It might be concluded that changes in plasma amino acid concentrations a re associated with the diminished vitamin B-12 status, but also the reduced feed intake and the possible reduction in bacterial activity in the rumen might contribute to these alterations. However, the marked changes in level s of homocysteine, methionine, taurine and serine in blood plasma may causa lly be related to a depletion of vitamin B-12 stores and may reflect the st ate of cobalt deficiency best.