Nitrates continue to be a concern for livestock producers as they deal with limited feed supplies over the fall and winter. Concentrations of nitrates can change as long as the plant is still growing and can respond to available moisture.
Fall cereal grains and cover crops - Wheat, rye, triticale and oats can accumulate nitrates. Test results have shown high nitrates this fall, and forages should not be grazed without testing for nitrates. This would include those that overwinter and might be grazed or hayed in the spring. Some of the brassicas such as turnips and radishes have had levels so high that their use for livestock feed will not be an option.
Crop residues - If an average or better grain yield was harvested, nitrates are less likely to be a problem in the crop residue left behind. However regrowth or volunteer growth in fields where grain production levels were substandard may contain problem levels of nitrate due to excess N fertilizer remaining in the soil. Sample the plant material you expect animals to graze, and in the case of fields with highly variable growth, collect separate samples that represent the different growth and maturity levels attained.
Baled forages with high nitrates - Sample each field or lot separately, because different fields or cuttings may have different nitrate levels present. The more samples you collect the better information you will have to make decisions. Nitrate concentrations tend to be highly variable within a field which can be reflected in individual bales. Storage will not decrease the nitrate concentration in baled forage.
The same sample that is used for a nitrate test can return information on protein and energy content. Corn hay baled earlier this summer is likely to be much higher in quality than corn residue baled after grain harvest. Applying the forage test information to a plan for feeding is an easy return on investment.
High nitrate feeds should be mixed with other feedstuffs to reduce the total nitrate concentration in the diet. Young, pregnant and stressed animals are more susceptible to nitrate toxicity. Make sure to consider nitrates from all components of the diet. This includes the water source. Introduce the high nitrate feed gradually over several days. Avoid situations where a large intake of high nitrate feed may occur in one meal. Over time, animals can adjust to higher levels in the diet. Feeding smaller amounts several times a day can be used to adapt cattle to nitrates. If grazing, gradually increase hours of access to the high nitrate feed.
A few pounds of grain (2-5 lbs) in the ration will dilute the nitrate in the total ration and provide the carbohydrates for bacteria to quickly convert the nitrogen into ammonia. Mixing of the ration should be thorough enough so that one animal does not have the opportunity to over consume the high nitrate component. Reduce the amount of the high nitrate component in the mix and begin a process of working back up if winter storms alter feeding patterns.
Silage - Test silage for nitrates before feeding. Silage can still contain toxic levels if the initial level was very high. Nitrates are reduced during ensiling however the reduction can range from 20 to 80%. Forage that was dry going into the silage pile may only have a 20% reduction.
Green forages generally provide the needed Vitamin A for cattle diets, however animal stores can be depleted in two to six months. High nitrates in feedstuffs may increase the requirement for Vitamin A. Given these considerations, providing supplemental vitamin A makes good sense and is not expensive to do. See March 2007 Beef tips for more on Vitamin A deficiency.
Horses - Horses are not nearly as susceptible to nitrate toxicity as ruminants. Some conversion of nitrate to nitrite occurs in the cecum but at a much lower rate than in ruminants. Pregnant mares can tolerate much higher levels than cattle but there is no published data on actual levels that horses can tolerate. Nitrate poisoning that does occur in horses happens more often in association with accidental fertilizer spills or water contamination.
This year has been abundant in nitrate challenges for producers. Incorporating high nitrate feeds into cattle diets can be done but it will require good management and attention to details.
Source: Sandy Johnson, livestock specialist