Winter forageWritten by Christy Hemken
Although there may be a tendency to neglect analyzing winter forage for nitrates after a wet summer, those in the beef forage and nutrition industries say nitrates are always a concern.
“Nitrates are always a concern, especially when hay prices are high and people are trying to find cheaper hay sources for their cattle,” says UW Beef Extension Specialist Steve Paisley.
Plants take up nitrogen from available soil sources during normal plant growth and they use soil-source nitrates to form protein. Since photosynthesis-formed sugars are also components of protein, anything that influences normal plant growth (such as drought) will reduce protein synthesis and nitrate can accumulate in the plant in higher than normal amounts.
In the animal digestive system, nitrate is converted to nitrite, which is absorbed into the blood and interferes with the normal transport of oxygen in the body. At low diet levels, nitrate poisoning produces sub-clinical conditions, which result in poor animal performance and a general lack of condition.
Jack Settlemire of Ranch-Way Feeds says nitrates can affect anything with red cells, and that horses and sheep aren’t nearly as likely to experience problems as cattle, but they are susceptible.
“It’s always a safe practice with non-grass or non-legume hays, like oat hay, to have them tested for nitrate levels as a safety concern,” says Scott Keith of the Wyoming Business Council.
“In most cases, the forages we are most concerned about are drought-stressed warm season annual forages such as sorghum/sudan cane hays and millet hays,” says Paisley. “Weed species such as kochia, lambsquarters, sunflower and pigweed can also accumulate nitrates, so emergency feed resources should be watched closely.” He says under extremely stressful conditions additional crops such as corn, wheat, oats and barley can also accumulate nitrates.
Settlemire says producers should never let their guard down with nitrates. “Even though someone tells me they have the forages more prone to nitrate toxicity under a sprinkler or flood irrigation, it’s always my strong recommendation to test anyhow,” he says.
“Do we need to be concerned?” asks Settlemire. “Theoretically? No. Responsibly? Yes.” He adds he thinks it’s of the utmost importance to test for nitrates even under the best conditions.
Paisley says high nitrate feeds are definitely a concern, but the concern and risk can be reduced by testing forage for nitrate level and managing the feed accordingly. “Plant nitrates are generally located in the lower one-third of the stalk. Raising the cutterbar when swathing, or reducing the grazing pressure so animals are not forced to graze the lower portion of the stalk, will help reduce the nitrate concerns,” he says.
Settlemire says the areas left for grazing after hay harvest are the most toxic parts of the plant, because nitrates are concentrated in the lower portion of the stalk. “A producer should turn his animals out on that pasture when they’re already full on grass or hay, and he should turn them out for a short period of time,” he says, recommending only 15 to 20 minutes at first. “The animals can be exposed slowly and adaptively to nitrates without overwhelming their systems.”
He says it’s important to fill the cattle before turning them out, because if they’re hungry they can consume enough forage to reach toxic levels even in the short time period of 15 to 20 minutes.
Feeds high in nitrates can also be diluted with a low-nitrate feed to reduce or eliminate risk. “I’ve recommended in the past that, when we know we’re going to use a feed with high nitrates, but not toxic levels, we feed the forage with alfalfa,” says Settlemire. “A person can dilute the amount of the forage high in nitrates by only feeding them as a fourth or a fifth of the diet.”
“When managing high nitrate forages, it is better to feed frequently, and don’t allow the cattle to go hungry,” says Paisley. “Also, it is important to manage feeding closely, especially during severe weather. If cattle go without feed for a day, they may go back and pick through the coarse stalks from previous feedings. Those lower stalks are where most of the nitrate is located, increasing the risk of nitrate problems.”
Settlemire adds the nitrate levels can be slowly raised. “The animal can adapt to high nitrates in the diet over a period of weeks, and we can increase the amount of forage high in nitrates without the worry of death loss.”
Feeding susceptible forages to growing, or non-pregnant, animals is the safest route, says Paisley. He also says producers should remember that nitrates remain in the plant no matter how long the hay is stored.
“Be aware of all sources of nitrates,” recommends Paisley. “Some stock water sources can be high in nitrates, adding to the risk. Also, poor water sources may reduce the herd’s water consumption, also adding to the problem.”
Settlemire says the best treatment for nitrate toxicity is prevention. He says there are treatment options available, but unless they’re on hand and administered immediately they do little good.