Minerals are essential for ruminant health, productivity, and metabolic function, with trace minerals playing critical roles at narrow dietary margins. Cobalt (Co) is essential as it supports ruminal microbial synthesis of vitamin B12 (cobalamin), which acts as a crucial cofactor in energy and protein metabolism. This review summarizes the role of cobalt in dairy cattle nutrition, emphasizing its contribution to vitamin B12 synthesis, propionate metabolism, and milk production. Only 3–15% of dietary cobalt is converted to vitamin B12, and efficiency depends on dietary composition, forage-to-concentrate ratio, and ruminal microbiome. Deficiency leads to reduced intake, poor growth, anemia, reproductive failure, and decreased milk yield. Cow’s milk contains ~0.5 µg/L of vitamin B12, with greater concentrations in colostrum; diet composition, supplementation, and genetics contribute to variability. Current recommendations set the cobalt requirement at 0.2 mg/kg diet DM, yet multiple environmental and nutritional factors can restrict vitamin B12 synthesis. Limitations of this review include heterogeneity among the studies reviewed, such as differences in trial design, animal genetics, diet composition, and environmental conditions, which may introduce variability and affect the generalizability and consistency of the findings. Collectively, findings highlight cobalt’s pivotal role in supporting microbial activity, energy metabolism, and production outcomes in dairy cows.

This study aimed to evaluate in situ ruminal nutrient degradation, fractional disappearance rate, and effective ruminal degradation of hydroponically sprouted barley, wheat, and triticale. Two ruminally canulated lactating cows were used in a complete randomized block design with four treatments and nine incubation times (0, 2, 4, 8, 12, 24, 48, 72, and 240 h). Treatments were corn silage (control), and sprouted barley, triticale, and wheat. Quadruplicate samples (5 g each) were placed in Dacron bags and incubated in the rumen. Then, bags were rinsed and spun, dried (48 h × 55 °C; 3 h × 105 °C), and weighed to determine residual dry matter (DM). Data were analyzed using mixed models (MIXED, SAS 9.4) with treatment, time, and their interaction as fixed effects, and cow and replicate (cow) as random effects. Denominator degrees of freedom were adjusted using the Kenward–Roger method, and means were separated by Tukey–Kramer. Significance was declared at p ≤ 0.05 and tendencies at 0.05 < p ≤ 0.10. Sprouted triticale and wheat treatments had a greater rapidly soluble fraction for DM (p < 0.01), the greatest fractional disappearance rate for DM (p < 0.01) and neutral detergent fiber (NDF; p < 0.01), and greater effective ruminal degradability (ERD) for DM (p < 0.01) and crude protein (CP; p < 0.01). Sprouted wheat also had the greatest ERD for NDF (p < 0.01). In contrast, sprouted barley had the lowest rapidly soluble fractions for DM (p < 0.01), NDF (p < 0.01), and CP (p < 0.01), lower fractional disappearance rate for DM (p < 0.01) and NDF (p < 0.01) than sprouted triticale and wheat, and the lowest ERD for DM (p < 0.01) and CP (p < 0.01). Overall, sprouted triticale and wheat had greater in situ ruminal nutrient degradation, effective ruminal degradation, and nutrient degradation kinetics, indicating their potential for inclusion in dairy cattle diets to improve nutrient degradability.