Too much of a good feed thing
January 22, 2015
When used properly, a feed additive called monensin – trade name Rumensin – can help improve feed efficiency, according to cattle nutritionists.
When fed at levels higher than recommended, problems occur.
Nutritionist and rancher Jeremy Martin said monensin, an ionophore, is used to enhance gut activity in cattle. The Nebraska man said Rumensin selects against methane-producing bacteria, improves feed efficiency and has anti-coccidiosis qualities. "It helps prevent bloat, helps encourage a more consistent intake of feed in feedlot cattle, and in pasture cattle it improves feed efficiency," he said. Martin feeds it to his own cattle.
Watertown, South Dakota, cattle feeder Bob Mack uses the granular form of Rumensin, built into a mineral pack, to supplement steers and heifers in his backgrounding and finishing lots.
"I like Rumensin probably the best because it tends to be the best coccidiostat and has substantial benefits as a bloat preventative," he said.
Mack also uses it in pasture situations, in mineral blocks or sometimes in tubs.
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One thing he's always been careful about is stepping his doses up gradually so as not to overdose an animal right away.
The product can be fed to feedlot cattle, beef cows, developing heifers in a lot or a pasture.
"It is important to remember that any feed additive, when fed at elevated doses can cause toxicity. This is not specific to Rumensin. Even in humans we can overdose on something that is normally very useful in proper dosages," said University of Nebraska-Lincoln cattle industry professor of animal science Galen Erickson.
The former beef feedlot extension specialist said overdoses, which cause acute toxicity, are quite rare but are usually caused by human error of some sort.
"Ensuring accurate feed ration formulation and accurate feeding at the time of the feeding is critical," he pointed out.
Some feed plants offer Rumensin in a combination product that includes protein, minerals, molasses and a binder to keep it suspended. When feeding such a product, the cattle feeder should recirculate the liquid every time it is used, Erickson said. "If it doesn't stay suspended, it can concentrate in the bottom of the tank and have the same impact (as feeding levels that are too high.)
Erickson said liquids are safe to use, but he cautions that circulation is key for the feed man. The use of well-proven suspending agents is critical at the feed plant, too, he said.
In addition to a settling or separation of a liquid feed additive, human error during the feed production or in delivery are other ways the product can be overdosed. For example, a new staff member at the feed plant might inadvertently deliver bags of the product in a dry form in a level 10 times what they usually use. Checking the labels of each bag of additive is always prudent, Erickson said, as is careful mixing at the feed plant to ensure accuracy in every bag or container.
Besides human error in feeding, mixing the concentrate (or lack of), preparing, labeling or other issues, toxicity can also happen when the product isn't adequately distributed in the ration and one animal gets a mouthful that contains enough product for several head.
Replacement heifers in a lot, for example, should take in 50 to 200 mg per head per day for increased rate of weight gain, according to a Rumensin informational sheet, "Tech Talk."
Erickson said when an overdose does occur, many feeders stop feeding the product for a few days. This is fine, he said, as is returning to the correct feeding level.
When acute toxicity or overdose does happen in levels 5 times the recommended dosage or more, heart problems can kill cattle. "Usually one to seven days after insult heart damage results in animal death," Erickson said. Caridac failure is the cause of death said "Tech Talk."
According to "Tech Talk," cattle can go off feed after consuming a 600 mg dose or more. Diarrhea, depression, shortness of breath and involuntary muscle spasms then occur before death when increasing amounts are fed.
Those animals that survive an overdose often go off feed, exhibit depression and diarrhea but then slowly recover.
Erickson said for two to four weeks following an overdose, cattle will be more weak and tired than usual so any handling or processing should not be done in this time period.
Mack expects that some animals that eat too much will suffer long-term stomach issues. "Are they ever going to be as efficient as they were? Some of the rumen populations won't recover. There could be some poor doers. Cattle could be pushed back several months until they recover and can rebuild those microbial populations. They might not hold or maintain condition after calving, or especially after their second calf. That is a touchy time for cows."
But Mack added that if a heifer is healthy enough to breed, she likely will be healthy enough to calve and go on to raise a calf, as the reproductive system is one of the most sensitive in a beef animal.
Dr. Clint Kesterson, Alliance Animal Clinic, has worked extensively with feedlot cattle.
He recommends ionophores for all of his feedlot-operating clients to decrease chance of coccidiosis and to improve rumen health and function in the cattle.
Lasting effects on cattle who survive an overdose include cardiac myopathies or abnormalities in the heart muscles, he said. The Alliance, Nebraska, veterinarian said the amount of damage to the animal's heart will be in proportion to the amount of Rumensin consumed, but that problems might go unnoticed until a stressful time like calving or late gestation. He also reminded people that Rumensin is a a good product when fed at recommended levels and should be measured with extreme care. "Read the label, calculate the dosage and read the label again," he suggests.
Kesterson said he doesn't know how likely it is to save their lives, but that cattle can be given mineral oil or activated charcoal to decrease the efficacy of the ionophore, block absorption and help speed its passing after an overdose has been identified. He suggested around 1 gallon of mineral oil for a 700 to 1,000 pound beef animal. A high roughage diet of prairie hay is also recommended after a toxic level has been ingested, he said.