Protecting cattle against nitrate poisoning

Source: Saskatchewan Agriculture and Food

There are all sorts of potential dangers from which cattle producers need to protect their herds. The hardest to defend against are those threats which can't be seen, like nitrate poisoning.

All plants contain some nitrate, but excessively high amounts are likely to occur in forage grown under stress conditions such as drought, frost, hail, low temperatures, herbicide applications or diseases.

Saskatchewan can experience all of these circumstances over the course of a regular growing season. Therefore, it's important for producers to be aware of the symptoms, preventative measures and treatments for nitrate poisoning in cattle.

The Farm Animal Council of Saskatchewan (FACS) has devoted one of its many "Cattle FACS" fact sheets to the subject to give producers more knowledge in this area.

"The information we provide through these fact sheets has been developed by committees of cattle care experts with specific knowledge in each of the topic areas covered," said FACS Executive Director Adele Buettner. "Our organization offered to co-ordinate the effort, produce the material and make it as widely available to producers as possible."

The fact sheet explains that, when growing conditions are favourable, plants take up nitrogen largely in the form of nitrate. The nitrate is rapidly converted to ammonia, which is incorporated into plant protein. Unfavourable growing conditions can interfere with nitrate use and cause it to accumulate in the plant. If the stress is removed and the plants recover, excess nitrate stored in the plant is usually metabolized over several days.

Under normal conditions, cattle convert the nitrate in the forage they eat to nitrite, which is then converted to ammonia and used by rumen microbes to make protein. Feed experts suggest that problems arise when nitrate converts to nitrite faster than nitrite converts to ammonia. When this occurs, nitrite accumulates and is absorbed into the bloodstream, where it binds with haemoglobin, thus reducing the oxygen-carrying capacity of the blood.

"In worst-case scenarios, animals can die by suffocation," Buettner said.

The amount of nitrate in plant tissue can be affected by other factors, such as the stage of growth. Nitrate concentrations in forage are usually higher in young plants and decrease as the plant matures. However, plants grown in soil with excessive nitrates, or those grown under stress might still have a higher content at maturity.

The parts of the plant closest to the ground also have the highest nitrate levels. Leaves contain fewer nitrates than stalks, and the seed (grain) and flower usually contain little or no nitrate.

Similarly, since nitrates in the soil are the source of nitrate in plants, a positive relationship exists between the two. However, the effect of nitrogen fertilization appears to be less significant in causing high nitrate content in forages than most other factors.

"Animal nutritionists say that some common cattle feed like alfalfa, vetch, trefoil, peas and clover generally do not accumulate nitrates," Buettner said. "However, they recommend that producers feed test their legumes to be sure they are not storing excess nitrates in the plant material."

According to the fact sheet, producers can still safely use feed that has higher-than-normal nitrate levels, provided they carefully manage their rations. Forage with high nitrate content can be diluted with grain or other forage low in nitrates. Feeding grain in combination with high-nitrate forage can help reduce the effect of the nitrate content because the energy from the grain helps complete the conversion of nitrate into bacterial protein in the rumen.

Frequent consumption of small amounts of high-nitrate feed can likewise increase the total amount of nitrate that can be tolerated by livestock, since it helps cattle to adjust to high-nitrate feeds. "Experts advise to feed long-stemmed forages, such as oats or barley hay, that contain high amounts of nitrate in limited amounts several times daily rather than feeding large amounts once or twice daily," Buettner said.

Under the right conditions, pastures can also accumulate nitrates. Risk can be reduced by providing supplemental feed that contains little or no nitrate, and grazing suspected pastures for limited periods each day for the first week to help cattle adapt. If possible, producers should not graze a suspected pasture until one week after a killing frost.

Should a producer's efforts to prevent nitrate poisoning fail, the fact sheet also offers some treatment instructions. "When the condition is first suspected, call a veterinarian immediately to confirm the tentative diagnosis and administer treatment," Buettner stated. "Handle the affected cattle as little and as quietly as possible to minimize their oxygen needs. Finally, remove the contaminated feed and replace it with a high-energy alternative, such as barley."

The Cattle FACS fact sheet on nitrate poisoning can be obtained from the organization's website at http://www.facs.sk.ca/ or by calling (306) 249-3227.

For more information, contact:
Adele Buettner, Executive Director
Farm Animal Council of Saskatchewan Inc.
Phone: (306) 249-3227
E-mail: facs@sasktel.net