Drought-damaged crops can be a suitable alternative feed but be careful of nitrates. When soil nitrogen is high and readily available, but the plant isn’t able to further metabolize it because of stress, nitrates can accumulate. Heavy nitrogen fertilization, drought stress, shading, cool and cloudy weather, high plant populations, shortages of soil phosphorus and potassium, hail, and grasshopper infestation can contribute to the problem. If it rains, nitrates will increase immediately, but after about two weeks of normal precipitation the plant will have resumed normal growth and nitrates won’t be a problem. In ruminants (cattle, goats and sheep), nitrates are reduced to highly toxic nitrites, which are reduced to ammonia. Bacteria in the rumen utilize ammonia to make protein. However, when too much nitrate is consumed, nitrite overloads the system and can’t all be converted to ammonia. As a result, nitrites get into the bloodstream, and reduce the ability of the blood to carry oxygen.
Nitrate levels are highest at the bottom of the stalk or stem, with less found up the plant. Grain and fruit will not accumulate nitrate. Examples of crops that can have nitrate problems are corn, oats, rye, flax, wheat, rape, soybean, alfalfa, and sweet clover. Certain weeds can contain high amounts of nitrate, too. You can use drought-stressed crops if you’re careful and if the nitrate level isn’t too high. Ensiling the crop for the proper amount of time (at least 3 weeks) can reduce levels by half or more. Green chop, on the other hand, must be fed the day it is cut because al-lowing it to heat will increase the nitrate toxicity potential. When making silage, chop to 3/8- to ½-inch length. This will help pack the silage more tightly and keep oxygen out as much as possible. High nitrate corn will produce more silo gas. Increase your cutting height to eight or 10 inches to avoid the lower part of the stalk. The ideal moisture content is 60 to 70% moisture.
If conditions persist, be careful when turning cattle out on corn stalks. If nitrates were high in the plant when corn was harvested, nitrates will stay high. When cattle graze corn stalks, they will eat the lower-nitrate and safer parts of the plant, such as the leaves, husks, cobs, and grain. As those parts diminish in the field, the cattle are forced to consume the higher-nitrate portions of the plant. If we have thin corn stalks caused by drought stress, cattle may consume more of the lower portion of these small stalks, making the potential for toxicity higher. If you baled any crops, nitrates will not generally decline in those, either. The situation may actually worsen if the crop is baled when wet, or if it gets excessively soaked at the bottom of large bales and stacks, because bacterial action can convert nitrates to toxic nitrites under those conditions.
Fortunately, ruminants can adapt to increasing amounts of nitrate if given time to adjust. Add suspect feeds into the diet slowly. In the case of corn stalks, cattle are exposed to higher-nitrate portions of the plant as the grazing period progresses and should be able to adapt over time. Feeding some grain will help them utilize ammonia and speed up the conversion of toxic nitrite to ammonia. Even though ruminants can adapt to high-nitrate feeds, there is a limit to the amount they can safely consume. The only way to know for sure if a feed is safe is to have it test-ed. A quantitative analysis, performed by a laboratory, can determine the amount of nitrate in a sample, telling you if the feed is safe for livestock. Call your local extension center for information on labs that can perform the nitrate analysis and for help interpreting the results.