Nitrate toxicity is a well-known metabolic issue in cattle associated with the amount of nitrate in the feed and water; however, it is a complex issue, especially in regards to grazing green forages. Once consumed by cattle, nitrates enter the rumen where microbes convert nitrate to nitrite in a rapid manner. Other microbes convert nitrite to ammonia, but at a much slower rate than those converting nitrate to nitrite. This rapid accumulation of nitrite in the rumen is then absorbed into the bloodstream, where nitrite binds with hemoglobin to form methemoglobin, thus reducing the oxygen-carrying capacity of the animal. As methemoglobin increases, symptoms of nitrate toxicity become worse. At low levels of methemoglobin dry matter intake and performance can be stunted. At moderate levels of methemoglobin, pregnant animals will abort. At high levels of methemoglobin incoordination and death can occur.
Nitrate values in feeds have been found to correspond to levels of methemoglobin in blood. For many years, a diagnostic test for nitrates has been recommended to determine if feed is “safe” or “toxic”. Luckily, toxic nitrate hays can be diluted to safe values with the addition of low or non-nitrate containing forages and/or grains. Depending on the testing laboratory and the method of reporting, the labs will provide a guideline for feeding of the nitrate forage. These values and recommendations are very accurate for dry, harvested forages; however, there is some question as to whether recommendations are equally appropriate for grazed, green, growing, high nitrate feeds.
As previously discussed, nitrate toxicity is a complex metabolic issue. Studies have shown several mitigation practices that can be successfully implemented in order to feed higher nitrate feeds. Some examples include providing a starchy feed such as corn, higher sulfur diets, and adaptation to high nitrate diets. In European studies, a higher level of nitrate in high moisture feeds such as fresh grass and turnips are required before similar methemoglobin levels are detected as compared to feeding hay. More research is needed to understand the complexity of nitrate toxicity and the safe use of feedstuffs containing high concentrations of nitrates.
Do you graze or hay annual forages? We need your help!
We want to hear about your experiences feeding or grazing high nitrate feedstuffs. Many annual forages /cover crops are known to accumulate nitrate in dry or cool conditions (such as during late fall or early spring). Our goal is to understand how often producers run into nitrate issues when using these forages so that we can help cattle producers through applicable research and extension programming. Fresh and dry forages act differently in the rumen, and the incidence of nitrate toxicity may reflect these differences in grazed verses hayed forages. The short survey (estimated time to answer these questions is 5 minutes) will be used to direct future research and extension programing.
Please complete the short survey by following the link below.
Annual Forage Nitrate Survey https://ssp.qualtrics.com/jfe/form/SV_2mek8zeFxbJU0Sh
This survey is a collaboration of the University of Nebraska and Kansas State Extension. Your answers will remain anonymous and confidential. We know your time is valuable and appreciate your help.