Which combination of grasses is commonly associated with high nitrate accumulation leading to methemoglobinemia?

• A. Timothy, fescue, bluegrass
• B. Rice grass
• C. Johnson grass, Sudan grass, millet
• D. Bermuda grass

Answer: (C)

High nitrate accumulation in forages is most characteristic of grasses in the Sorghum family when they’re stressed, such as during drought or with heavy nitrogen fertilization. In ruminants, nitrate is reduced to nitrite in the rumen, and nitrite converts hemoglobin to methemoglobin, which cannot carry oxygen effectively, leading to methemoglobinemia. Johnson grass, Sudan grass, and millet are classic high-nitrate accumulators and are well known to cause this condition when grazed or fed. By comparison, cool-season grasses like timothy, fescue, and bluegrass typically don’t accumulate as much nitrate under normal conditions, and Bermuda grass is less commonly implicated. So the combination of Johnson grass, Sudan grass, and millet best fits the scenario of high nitrate–associated methemoglobinemia.