Supplementing lactating dairy cows with a vitamin B12 precursor, 5,6-dimethylbenzimidazole, increases the apparent ruminal synthesis of vitamin B12

Abstract

Cobalamin (CBL), the biologically active form of vitamin B 12 , and its analogs, are produced by bacteria only if cobalt supply is adequate. The analogs differ generally by the nucleotide moiety of the molecule. In CBL, 5,6-dimethylbenzimidazole (5,6-DMB) is the base in the nucleotide moiety. The present study aimed to determine if a supplement of 5,6-DMB could increase utilization of dietary cobalt for synthesis of CBL and change ruminal fermentation, nutrient digestibility, omasal flow of nutrients and ruminal protozoa counts. Eight ruminally cannulated multiparous Holstein cows (mean ± standard deviation = 238 ± 21 days in milk and 736 ± 47 kg of BW) were used in a crossover design. Cows were randomly assigned to a daily supplement of a gelatin capsule containing 1.5 g of 5,6-DMB via the rumen cannula or no supplement. Each period lasted 29 days and consisted of 21 days for treatment adaptation and 8 days for data and samples collection. Five corrinoids, CBL and four cobamides were detected in the total mixed ration and the omasal digesta from both treatments. The dietary supplement of 5,6-DMB increased (P = 0.02) apparent ruminal synthesis of CBL from 14.6 to 19.6 (s.e.m. 0.8) mg/day but had no effect (P > 0.1) on apparent ruminal synthesis of the four analogs. The supplement of 5,6-DMB had no effect (P > 0.1) on milk production and composition, or on protozoal count, ruminal pH and concentrations of volatile fatty acids and ammonia nitrogen in rumen content. The supplement had also no effect (P > 0.1) on intake, omasal flow and apparent ruminal digestibility of dry matter, organic matter, NDF, ADF and nitrogenous fractions. Plasma concentration of CBL was not affected by treatments (P = 0.98). Providing a preformed part of the CBL molecule, that is, 5,6-DMB, increased by 34% the apparent ruminal synthesis of CBL by ruminal bacteria but had no effect on ruminal fermentation or protozoa count and it was not sufficient to increase plasma concentrations of the vitamin. Even though the efficiency of cobalt utilization for apparent synthesis of CBL was increased from 2.0% to 2.7% by the 5,6-DMB supplement, this improved efficiency was still very low. Further research is needed to identify the factors affecting efficiency of utilization of cobalt for synthesis of CBL by the bacterial populations in rumen.Keywords: dairy cow, vitamin B 12 , cobalt, 5,6-dimethylbenzimidazole, ruminal microflora ImplicationsUnlike other B vitamins, vitamin B 12 is not present in plants and is produced only by bacteria if cobalt supply is adequate. Therefore, dairy cows rely on synthesis of the vitamin by the bacteria present in rumen to cover their requirements. However, the proportion of cobalt used for these syntheses is low. Providing a preformed part of the vitamin B 12 molecule (5,6-dimethylbenzimidazole) increased by 34% apparent synthesis of the vitamin by ruminal bacteria but failed to increase substantially efficiency of cobalt utilization. The results highlight the lack of knowledge on nutritional factors driving ruminal pr...

High-concentrate diets based on forages harvested at different maturity stages affect ruminal synthesis of B vitamins in lactating dairy cows

“…Plant maturity and ruminal B-vitamin synthesis to ARS reported by Castagnino et al (2016) and Brito et al (2014). However, ARS reported in current trials were approximately eightfold less than values reported by Santschi et al (2005a) and Schwab et al (2006), even though the total cobalt concentrations in our diets (ranging from 1.27 to 1.64 mg/kg DM) were similar to those studies.…”

Relationship between Vitamin B12 and Cobalt Metabolism in Domestic Ruminant: An Update

“…The molecule is made up of four main parts: the corrin ring (similar to that found in heme, chlorophyll and cytochromes); the remaining nucleotides; the aminopropanol residue that binds the nucleotide to the corrin ring and the ligand B attached to the cobalt atom as the central nucleus of the corrin ring [ 12 , 13 , 14 , 15 , 16 ]. In cyanocobalamin (CBL), 5,6-dimethylbenzimidazole (5,6-DMB) is the base in the nucleotide fraction ( Figure 1 ) [ 17 ].…”

“…Even the ciliated protozoa present in the rumen need vitamin B12, which they obtain from ruminal bacteria that synthesize vitamin B12 [ 17 ]. In addition, these bacteria, present in the rumen, use dietary cobalt to produce vitamin B12 analogs, molecules chemically related to cyanocobalamin but devoid of biological activity [ 17 , 21 ].…”

“…Even the ciliated protozoa present in the rumen need vitamin B12, which they obtain from ruminal bacteria that synthesize vitamin B12 [ 17 ]. In addition, these bacteria, present in the rumen, use dietary cobalt to produce vitamin B12 analogs, molecules chemically related to cyanocobalamin but devoid of biological activity [ 17 , 21 ]. The production of vitamin B12 by ruminal microflora, as with folates, is generally considered sufficient to avoid deficiency symptoms in ruminants [ 12 , 22 ], although, in steers, it has been shown that the ruminal microflora extensively destroys dietary folic acid and vitamin B12 [ 22 , 23 ].…”

“…The amount of cobalamin synthesized depends on multiple factors, including the composition of the ration (ratio of forage to concentrate; fiber content) and dry matter intake [ 20 ]. However, it has long been recognized that the most important factor for the production of vitamin B12 and analogs synthesized by ruminal bacteria is the concentration of cobalt in the diet [ 9 , 17 , 20 ]. Without cobalt in the diet, ruminal production of vitamin B12 decreases rapidly (within a few days).…”