Dietary Co is essential to ruminal vitamin B12 formation by microbes. The majority of research related to dietary Co was based on temperate forages and feeding systems. Therefore, it is vital to study the effect of Co supplementation on tropical forages and feeding systems. Fifteen dairy cows (Jersey) weighing 283 ± 30.9 kg were allocated separately to three dietary treatments in a 3 × 3 Latin Square Design with 3 periods of 28 days duration, with 21 days of adaptation followed by 7 days of sampling. The dietary treatments (mg supplementary Co/kg DM) were: 0 (Control: CON), 0.2 (COL) and 0.4 (COH). The cows were fed a basal forage mix (75% Guinea grass; Panicum maximum and 25% of CO3; Pennisetum purpureum) ad libitum. Animals were individually stall tied and machine milked at 0600 and 1600 hours (h), and feed intake and milk yield were recorded daily during the sampling week. Faecal samples were collected during the final five days of the sampling period, and blood samples were collected by jugular venepuncture. Dry matter (DM) intake increased (P<0.05) with increasing dietary concentration of Co. In contrast, there was no effect (P>0.05) of dietary treatment on milk yield or fat content, with mean values of 4.01 kg/d and 41.3 g/kg, respectively. Similarly, there was no effect (P>0.05) of dietary treatment on whole tract digestibility of DM, N, or fibre. Mean plasma mineral concentrations of Co, Fe, Zn, Cu, Mn, and Se were 0.42, 36.9, 13.6, 15.5, 3.50, and 2.29 mol/L, respectively. Plasma glucose and vitamin B12 levels were not affected by the treatments and had mean values of 65.5 mg/dL and 746 pmol/L, respectively. In conclusion, the addition of Co increased intake, but did not alter performance, whole tract digestibility, plasma mineral levels, and glucose and vitamin B12 contents in Jersey cows managed and fed under tropical conditions.