Effects of novel organic sources of cobalt on ruminal fermentation, nutrient degradation and vitamin B12 synthesis in vitro.

Cobalt (Co) is essential for vitamin B12 synthesis in the rumen and energy metabolism in cattle. Previous studies on organic Co sources have shown variable effects on dairy cows' performance, focusing primarily on Co glucoheptonate as an alternative to the traditional Co carbonate (CoCO3). Our objective was to evaluate the effects of novel organic Co sources on ruminal microbial fermentation, nutrient degradation, and vitamin B12 synthesis using a dual-flow continuous culture system. We used eight fermenters in a duplicated 4 × 4 Latin Square design, where each -fermenter was provided daily with 106 g DM of a basal diet plus the corresponding Co treatment. The treatments consisted of supplementing 1 mg Co/kg DM from the following Co sources: (i) CoCO3, (ii) Co Pectin (CoPec), (iii) Co Amino Acid (CoAA), and (iv) Co Pectin + Co Amino Acid (CoPec+CoAA). Data were analyzed with the MIXED procedure of SAS 9.4 to evaluate the effect of Co source on pH, VFA, N metabolism, vitamin B12 concentration and flows, and nutrient degradability. We did not find an effect of Co source on pH (P = 0.92) or concentrations of acetate (P = 0.32), propionate (P = 0.15), butyrate (P = 0.92), and other VFA. However, we found that D-lactate concentration was greater in CoCO3 than other treatments (P = 0.03), and total lactate was greater in CoCO3 compared to CoAA and CoPec+CoAA (P = 0.04). Vitamin B12 in liquid outflow tended to be lower with CoCO3 (P = 0.10). Moreover, there was greater bacterial N flow (P = 0.01) and also greater N use efficiency (P = 0.01) in CoAA than CoCO3 and CoPec. For nutrient degradation, we found a greater ruminal degradability of NDF (P < 0.01) in CoAA and CoPec+CoAA compared to CoCO3 and CoPec. Our results indicate that, at a supplementation rate of 1 mg Co per kg diet DM, the tested Co sources affected fermentation of ruminal contents in continuous culture. Specifically, under the conditions of this experiment with dairy cattle diets, CoAA promoted greater microbial protein synthesis, NDF degradability, and liquid-associated vitamin B12 flow compared to CoCO3 and CoPec, suggesting enhanced Co utilization by ruminal microorganisms when CoAA is included as the primary Co source in the diet.