Nutritional deficiencies in mineral metabolism have been described or suspected in managed and wild ungulate populations. In blesboks (Damaliscus pygargus phillipsi), clinical signs of copper deficiencies have been described in the wild as well as in captivity. Plasma concentrations of cobalt (Co), copper (Cu), iodine (I), manganese (Mn), selenium (Se), and zinc (Zn) were measured over a 6-mon period by inductively coupled plasma mass spectrometry in two groups of five apparently healthy blesboks from a single zoological collection. The control group did not receive any treatment, whereas animals from the treatment group were given an oral drench in October with two sustained-release trace element ruminal boluses (Oligovet ovin-caprin 6 g bolus, Vetalis, 16100 Chateau Bernard, France). Plasma samples were obtained prior to the start of treatment (October) and in November, February, and April following treatment. No significant differences were found between treatment and control groups for any of the measured minerals over the course of the study. The plasma concentrations of Co, Cu, Se, and Zn were significantly different (P < 0.05) over time for all individuals, but this effect could not be linked to a change in the diet or husbandry. Copper plasma values fluctuated between deficient and normal ranges for cattle. Zinc plasma values were within a range consistent with deficiency in cattle. The great variability of these results should prompt caution in the interpretation of the efficacy of oral trace mineral intake or the expected effect of a dietary modification on trace mineral status based on plasma values.