Besides limiting forage production, dry weather can create another problem for producers to deal with, that of nitrate toxicity. Nitrogen is one of the big three macro-nutrients, along with potassium and phosphorus, that plants use in large amounts. While all plants use nitrogen, some tend to be more likely to have high nitrate levels than others. Annual grasses like cane, millet, oats, and even corn often have elevated nitrate levels. So do certain weeds like pigweed, kochia, and lambsquarter.
When growth stops due to stress like drought, plants continue to uptake nitrogen if they can. However, with nowhere for this nitrogen to be used up, it collects in the lower part of the stem as nitrate. When livestock consume this high nitrate forage, we have issues.
While the return of moisture can revitalize plant growth and provide a place for extra nitrate to be used, it doesn’t happen all at once. In fact, for several days after a drought breaking rain, nitrate levels in plants may be higher than they were during dry weather. The moisture has allowed for the plant to begin absorbing nitrogen through the root system again, but often times growth is slower to start up again. If your plants still look stressed and haven’t returned to normal growth after a rain storm, chances are you still have higher than normal nitrates.
As with any feed issue, the best way to protect against nitrate risk is to know what we have to deal with. Testing any feed suspected of being high in nitrates is a good idea. Even when tests come back high, it doesn’t mean these feeds are unusable, we just have to deal with them appropriately.
Most recommendations for the level of nitrates in forages that cause issues are based on hay, with levels above 2,100 ppm N03-N considered toxic. Often grazing cattle can tolerate greater concentrations of nitrates than those consuming hay. The amount of nitrates cattle can consume without an issue depends a lot on the situation and management. First, fresh forage releases nitrates slower into the rumen than hay. Second, we can manage grazing so lower portions of the plant where the highest concentration of nitrate is found are not utilized. This is especially important early on in the grazing period. Rumen microbes can adjust to high nitrate levels and adapt over time, detoxifying higher and higher levels of nitrate. Allowing animals to be selective when grazing high nitrate forages can aid in this transition. Finally, additional energy in the rumen can help microbes increase detoxification. Safely supplementing some grain to animals grazing mature high nitrate forages can lower risk.
Hay produced from high nitrate forage may be the most difficult to deal with. Properly cured and stored, hay will lock in nitrate levels at where they were during harvest. It’s essential in these cases to get a nitrate test on any questionable hay so we can plan to feed these bales safely. Diluting the diet with grain or low nitrate forages is most common way to utilize high nitrate hay. Frequent, small meals that slowly increase the amount of nitrate fed helps cattle adapt to high nitrate hay, especially if low nitrate forage can be supplied beforehand to prevent overeating. Ensure access to low nitrogen fresh water. Last, don’t feed wet or damp high nitrate hay. Moisture will speed up digestion and can case toxicity where we may not have had an issue with a dry bale.
Our final harvest option is ensiling. Silage harvest, unlike grazing or hay, has the potential to actually reduce nitrate levels in a feed up to 50%. Proper fermentation is essential for this to happen and to ensure a quality feed, so make sure to watch moisture levels, pack well, and cover silage once chopped. Silage that we consider high in nitrate shouldn’t be sampled until it has fermented and we are ready to feed out to get an accurate assessment of nitrate levels.
Nitrate concerns are nothing to sneeze at, but with the right tools, can be managed safely. Keep animals from using lower portions of a plant that have highest concentrations and work them up to high nitrate feeds slowly. Test hay you think may have an issue, especially annual grasses and hay with a high percentage of weeds. If tests come back high, plan to feed safely by dilution. Silage may be the preferred option for those looking to reduce nitrate levels as opposed to managing risk.
-Ben Beckman is a beef systems Extension Educator serving the counties of Antelope, Cedar, Knox, Madison and Pierce. He is based out of the Cedar County Extension office in Hartington. You can reach him by phone: (402) 254-6821 or email: ben.beckman@unl.edu