High nitrate concentrations in feedyard water supplies can pose a significant health risk to cattle. Nitrate itself is not particularly toxic, cattle convert it to nitrite, which is ten times as toxic, in the rumen.

Recently released data from the U.S. Department of Agriculture’s National Animal Health Monitoring System (NAHMS) indicates that most feedyard water supplies have low or undetectable concentrations of nitrate, but some might be marginal. NAHMS sampled water from 263 feedlots in 10 states and found that 41 percent had nitrate concentrations that were undetectable or less than 10 milligrams per liter. About one-quarter had 45 to 132 mg/L and 4.2 percent had greater than 220mg/L. None of the water samples exceeded the recommended limit of 440mg/L.

The data shows, however, that nitrate concentration tends to increase with well age and in shallow wells. Researchers note that the safe limit for nitrate concentration could depend on other factors, particularly nitrate levels in feed ingredients. They also note that while levels below the recommended limit may not cause clinical disease, they could suppress animal performance.

These results suggest that feedlot operators should monitor the nitrate levels in their water supplies, particularly if using old or relatively shallow wells.