Basils include approximately 150 species, mostly from Asia, Africa, and South America that have spread throughout the world as culinary and ornamental herbs. Basil is grown as an annual in most zones under 8 since it dies down at the first frost.
Nitrite toxicity to livestock consuming excessive concentrations of nitrates in forages has been well documented in the scientific literature. The following excerpt by Ball, et al. (1991) summarizes the knowledge on this topic.