AIRDRIE, Alta. – Plenty of salvage feed is available this year, but producers need to watch for high levels of nitrates and sulfur.
Canola hay has more protein and energy than other forages, but it may also contain more sulfur. As well, nitrates could be high if the canola was cut because it was damaged.
“They are not difficult to deal with if you know how,” Cargill beef consultant Bryan McMurry told an Oct. 5 winter feeding seminar in Airdrie.
“It is the not knowing that will get you.”
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If tests show high levels of nitrates or sulfur, feed should be given to cattle in limited amounts and blended with other feed that doesn’t contain either toxin. Too much sulfur can lead to neurological problems and a form of polio. If the toxins are present in high amounts, he added, feed cannot be blended successfully.
Sulfur produces hydrogen sulfide gas in the rumen. Cattle can breathe most of it in, which eventually goes into the bloodstream and affects the brain.
“A certain amount of sulfur in the diet is a danger,” McMurry said.
However, polio is rarely seen and may affect only a few animals in the herd. It is not usually a problem in grazing situations but may appear in feedlot diets where the rumen acid is high and animals receive dried distillers grain. It could be exacerbated if sulfur is also in the water.
Most forage has some level of nitrates that have accumulated under stress from drought or frost or in heavily fertilized crops.
Nitrates are not toxic but nitrites are toxic. Rumen microbes use nitrogen to turn nitrates into nitrites and then into ammonia to create amino acids, which the animal needs. Excess ammonia is absorbed by the blood and passed in the urine as urea. This occurs when the nitrate breakdown system is in balance and no surplus of nitrites accumulate.
Nitrate poisoning occurs when nitrite levels in the rumen exceed the capacity of the microbes to convert it to ammonia. If there is too much ammonia, it seeps through the rumen wall and into the bloodstream, where problems develop.
The overload could asphyxiate the animal because of a lack of oxygen in red blood cells.
Monogastrics such as horses and pigs convert nitrate to nitrite in the intestine closer to the end of the digestive tract, so there is less chance for the nitrites to be absorbed by the blood.
Cereal hay and silage tend to be the most prevalent for nitrates, although they are also found in weeds such as kochia, pigweed, thistle and wild oats.
Legumes have more protein but do not store it in nitrate form.
Feed testing is important if nitrates are suspected.
There is nothing to worry about if the test comes back with levels at less than 1,500 parts per million, but levels of 1,500 to 5,000 ppm could mean problems for pregnant cows. If this is the case, feed could be mixed 50-50 with hay that is at zero levels.
Feed that tests at more than 5,000 ppm should not be fed to pregnant animals and little of it should be used. Feed should not be used at all at rates of more than 10,000 ppm. It may need to be plowed into the soil.
Nitrates do not disappear over the winter as the feed sits, so feed blends need to include a lot of starch, which is broken down into sugar to which the microbes and cattle can adapt.
“If you were feeding really low quality straw, you have some real problems because those carbohydrates are bound up in the fibre and there is very little starch available, “ McMurry said.
Silage should be tested for nitrates after the ensiling process has stopped. This could be done when other feed tests are completed.
Alberta Agriculture says nitrate levels may be reported in three different ways depending on the analytical procedure used: nitrate (N03), nitrate nitrogen (N03-N) or potassium nitrate (KN03).
