Cobalt deficiency is associated with increased susceptibility to disease development and reduced immune system function, as this mineral enhances the action capacity of neutrophils in sheep, and vitamin B12 deficiency, which results from it, can lead to a reduction in CD8+ Th lymphocytes and NK cells, thereby reducing the effectiveness of the immune system and increasing the likelihood of contracting diseases, especially of an infectious nature [44,45]. The gene discussed is CD8A; the disease is vitamin B12 deficiency.