Almost as predictable as the coming of the winter season will be the quickly spread horror story of the death of several cows from a herd that was fed "the good hay" for the first time after the snow storm. Ranchers that have harvested and stored potentially high nitrate forages such as forage sorghums, millets, sudangrass hybrids, and/or johnsongrass, need to be aware of the increased possibility of nitrate toxicity. Of particular concern, is the scenario whereby the cows are fed this hay for the first time after a severe winter storm. Cattle can adapt (to a limited extent) to nitrate intake over time. However, cattlemen often will feed the higher quality forage sorghum type hays for the first time during a stressful cold wet winter storm. Cows may be especially hungry, because they have not gone out in the pasture grazing during the storm. They may be stressed and slightly weakened by the cold, wet conditions. This combination of events makes them even more vulnerable to nitrate toxicity.
The rancher is correct in trying to make available a higher quality forage during severe winter weather in an effort to lessen the loss of body weight and body condition due to the effect of the wind chill. But if the forage he provides to the cows is potentially toxic, his best intentions can backfire.
The best approach would be to know ahead of time what is the concentration of nitrate in the hay. Have representative sample of the hay tested by a reliable laboratory. If the producer is confident that the hay is very low in nitrate content then use of the hay should be safe. If the nitrate content is unknown, then precautions should be taken. Feeding small amounts of the hay along with other grass hays during the fall and early winter days can help to "adapt" the cattle to the potential of nitrate. This is not a sure-fire, 100% safe concept. If the hay is quite high in nitrate, it can still be quite dangerous. Diluting the high nitrate feed with other feeds can reduce (not eliminate) the likelihood of problems.
If the rancher has no choice but to feed, unknown sorghum-type hays during a snow storm, he or she should plan to watch the cattle carefully for 8 to 12 hours after feeding to be ready to remove the cattle from access to the high-nitrate forage, if symptoms of nitrate toxicity appear. Nitrate toxicity causes the blood to be lose its oxygen-carrying capability. Watch for cattle that are panting, staggering, disoriented, or other signs of asphyxiation.