FALL GRAZING PROBLEMS by Mike Mehren Ph.D.

FALL GRAZING PROBLEMS
by Mike Mehren Ph.D.

During the fall, some operations are lucky enough to have irrigated meadows, hay fields, and other sources of green feed available for the cows and calves. I have already had calls regarding fog fever and nitrates. These two nutritional maladies can take the humor out of extending the grazing season and providing good rates of gain. Both happen quite rapidly, and can lead to the death of many animals at once.

Fog fever, cow asthma, or grunts are the names given to a disease also known as pulmonary emphysema. It occurs when cattle have been grazing dry feed and are suddenly moved to lush meadows or irrigated pasture. Many cattle in the Northwest have been grazing very dry mature feed for quite some time this summer. The problem seems to be caused by a high concentration of the amino acid tryptophan in the forage.
This amino acid is a normal portion of the amino acids that make up forage protein, but apparently when the animals have grazed dry mature forage, that had little tryptophan, are moved to lush, high protein forage that has an abundance of Tryptophan the microbes in the rumen don’t break it down into it’s normal compounds that are non-toxic. Instead it is broken down into a toxic compound that affects the lungs.

Typically this disease affects the most aggressive animals in the herd. Mature cows are the ones most susceptible to this disease as opposed to calves or yearlings. The symptoms include breathlessness and open-mouthed breathing or panting. It is obvious that the animals are in distress. The disease progresses rapidly and can kill many animals. It occurs during the first week or two after the cattle have been moved onto the lush feed.

Years ago, when grazing turnips was very popular, I believed it was related to something in the turnip, but that isn’t the case. It can occur on grass, triticale, alfalfa, and other irrigated crops. Frost changes the forage in such a way that there is much less chance of the animals getting pulmonary emphysema if grazing can be delayed until then.

I know of no treatment for pulmonary emphysema. If possible, the animals should be moved to a drylot and fed hay. Unfortunately, pushing the sick animals may cause their death. Your Veterinarian may give them something to ease pain and give them a chance to recover on their own. Animals having this disease never fully recover because of damage to the lungs. They may have to be culled.

Since there is no treatment, the best that can be done is to practice prevention. This can be done in several ways. Turning yearlings or sheep in ahead of the cow herd helps, because those animal will graze the ‘lushest’ forage, leaving the less toxic plants for the cows to graze. Cows can be introduced to the forage over a week to ten days. You might turn the cows into a pasture that you believe is dangerous for the first time in the afternoon when they are full, and then only allow 1 or 2 hours grazing time. This process could be continued so that by the 10th or 12th day they are allowed to graze full time.
Another means of prevention is to feed a supplement containing one of the feed additives known at Rumensin or Bovatec. Both of these products affect the microbes in the paunch so that the toxins aren’t produced. A supplement with either of these products should be offered to the cows two weeks prior to grazing the suspect pasture and continued for at least two weeks after they are turned in. The trick to using one of these feed additives is to get all of the cows to eat it on a regular basis. With any free choice supplement, sometimes that just doesn’t happen no matter what you try. You might try using extra feeders to give as many animals as possible access to the supplement at any one time.

Nitrate is a form of nitrogen that accumulates in many different forages. We normally think of turnips, sudangrass, oats, pigweed, and lambsquarter as being crops that accumulate nitrates. However other grasses and alfalfa can accumulate nitrates. I recently ran across several cuttings of alfalfa that had very high levels of nitrates. They had been irrigated with waste water from one of the vegetable processing plants Nitrate accumulation occurs during periods of stress, such as frost and high temperature, following herbicide application, some plant diseases, drought, or hail damage. It may also occur when a field has been fertilized with nitrogen that the plants have not been able to metabolize into plant protein. Nitrates are only dangerous to ruminants such as cattle, sheep, llamas, deer, and elk. Nitrates are not dangerous to horses or pigs. The reason nitrates are dangerous is that the bugs in the paunch convert the nitrate to nitrite, which is then absorbed into the bloodstream. Once it gets there, the nitrogen replaces oxygen, so the animal suffocates because oxygen doesn’t reach all of the cells. If you happen to see animals suffering from this problem, they will be gasping for air; most of the time they are down before they are found.

Nitrates are also found in water. We usually hear about it in relation to drinking water for humans. High nitrate levels have been associated with the birth of ‘blue babies’ so mothers are warned against drinking water high in nitrates. Livestock can also be harmed by high nitrate water when the feed also has a high nitrate level. The nitrate in the water is additive to the nitrate in the feed. Either feed or water alone may not be toxic, but when both are consumed, they may be dangerous. I have not encountered water that was high enough in nitrates to be dangerous to livestock. That isn’t the case for feed.

If you suspect a possible nitrate problem; take a forage sample and send it to a feed testing lab for nitrate analysis. The report will look something like the table below.

POTENTIALLY LETHAL LEVELS OF NITRATE IN FEED DRY MATTER
Analytical Value	Percent	Parts Per Million
	.............100% dry basis..............
Nitrate Nitrogen(NO3-N)	0.21	2100
Nitrate Ion (NO3)	0.9	9000

Labs report nitrates in one of the two ways shown above. If your feed sample has one of the values shown above, it is TOXIC! Unfortunately nitrates aren’t uniformly distributed around a field or lot of hay. Do a good job of sampling, and if your results are near those shown, consider taking action to prevent toxicity.

I use an upper limit of 0.11% or 1100 ppm for NO3-N, and 0.45% or 4500 ppm for NO3. This is about one half the level considered to be toxic. Fortunately for us the animals will adapt to nitrates in a manner similar to urea. If you dilute the nitrates by feeding some other feed having no nitrates, the high nitrate feed can be used. For example:

Alfalfa Hay, 18% protein No Nitrates found.
Sudangrass Hay, 14% protein. NO3-N 4000 ppm found.

Week 1. Feed a mixture of 75% alfalfa hay and 25% sudangrass hay. Nitrates have been reduced to 1000 ppm in the total feed ration
.
Week 2. Feed a mixture of 65% alfalfa hay and 35% sudangrass hay. Nitrates are now at 1400 ppm.

Week 3. Feed a mixture of 40% alfalfa hay and 60% sudangrass hay. Nitrates are now 2400 ppm
.
Week 4. Feed 100% sudangrass. Nitrates are now 4000 ppm; the animals have adapted to the nitrate nitrogen and will use it like any other source of nitrogen.

Your Veterinarian should treat nitrate toxicity. If you just happen to have a gallon of vinegar on hand and know how to tube a cow, you can prevent the nitrate from being converted to nitrite. This conversion is slowed considerably when the paunch is acid rather than neutral or basic which is normal when cattle are grazing forages.

You can test for nitrates before feeding or turning cattle into a forage that you suspect might be high in nitrate. It costs about $10.00 and can usually be reported to you the following day. Unfortunately there is no test that will help you with fog fever. If you feel lucky, just go on with it. If you have my luck you might make sure the animals are full and turn them in during the afternoon. You might even consider penning them that night and repeating this process but allowing longer grazing each day for the first week or so.

Michael J. Mehren hasn’t had fog fever yet, but admits to a mild case of buck fever now and then. He may be contacted by Email at mehrens@eotnet.net.