Producers intending to make silage or bale greenfeed from crops that have been frozen in the field need to take time to ensure that the feed is nitrate-safe.
“The threat to livestock from nitrate accumulation in forages is that the nitrates bind with the red blood cells in the blood, reducing the animals’ ability to move oxygen to the tissues,” says Barry Yaremcio, beef and forage specialist with Alberta Agriculture and Rural Development. “This causes the animals to suffocate from the inside and, if the concentrations are high enough, the animal will asphyxiate and die from a lack of oxygen. When feeding cows in the last 30 days of pregnancy, if nitrate levels are high during that feeding period, it can cause spontaneous abortion of the calf.”
Making silage out of frozen crops is a good practice but the silage must be tested to determine quality and nitrate content. To get a representative sample, take a handful of green chop material out of each load, put it in a five-gallon pail and mix it together. Fill approximately half of a bread bag full of the sample, squeeze the air out of the bag, seal and freeze it and then send it to a laboratory for analysis. If making greenfeed, use a forage sampler to get a representative sample for analysis.
When baling greenfeed, round or square, if moisture levels are too high, the material will start to heat and can actually reach over 40C. If that happens, nitrate will be converted to nitrite which is 10 times more toxic than nitrate. If nitrate accumulation is at all a concern, the greenfeed must be dry before it is baled.
“Work done in the early 1960s established 0.5 per cent as the toxic level of nitrates in feed,” says Yaremcio. “This level was arrived at by administering sodium nitrate directly into an animal’s blood stream, but this established a false level for ingested nitrates. Forages do not have the ability to go immediately into the blood stream in a concentrated form as it takes two to three days for the material to be digested. Therefore, nitrates at levels of 0.7, 0.9 even up to one per cent can be fed if introduced slowly and time is taken to acclimatize animals to that level of nitrates. Just remember that care must be taken.”
For further information on nitrate accumulation, visit Alberta Agriculture’s website at www.agriculture.alberta.ca/publicationsto view the fact sheet Nitrate Poisoning and Feeding Nitrate Feeds to Livestock.