More positive samples, higher concentrations than in previous years
posted January 1, 2010
One of Dr. John W. Hicks' clients lost about 100 swine after a 4,000-head herd ate feed produced from corn that had sustained hail damage prior to harvest.
The corn producer did not know the feed contained a relatively high concentration of vomitoxin, a fungal toxin that can develop on various grains including corn, wheat, rye, and barley.
"The pigs refused to eat feed, even though it was aptly available to them," Dr. Hicks said. He later added, "There was actually a fairly high number of gastric ulcers as a consequence of them being off feed."
Dr. Hicks, of Carroll, Iowa, has warned other clients about the risks posed by mycotoxins, and he thinks the molds will continue causing animal health problems for some producers this year. Feed mills and manufacturers are testing for mold, but it is difficult to gauge how much money and effort to put into such testing when hundreds of thousands of bushels are moving through the mills.
Dr. Steve Ensley, a clinician with the Iowa State University Veterinary Diagnostic Laboratory, said that, in any given year over the previous decade, it has been rare for more than 5 percent of samples arriving at his laboratory to test positive for any of the five most common mycotoxins. In 2009, about half of all samples tested positive, and many of them had substantially higher mycotoxin concentrations than were seen in previous years.
A press release from the university stated that cool, wet weather in the growing season and rain in the fall delayed 2009 harvests in some areas and increased the risk of mold development, which can lead to increases in mycotoxin formation. The university's veterinary diagnostic laboratory has found a higher than normal incidence of affected corn across Iowa and in samples from six other states.
Samples from previous years were unusual if they contained 1 ppm of a vomitoxin, Dr. Ensley said, but a substantial number of this year's samples contained between 1 ppm and 15 ppm. He has not heard of many animal illnesses so far, but he—like Dr. Hicks—said there is a "really good possibility there are going to be some health issues with this year's corn."
Dr. Hicks said swine practitioners are most nervous about zearalenone, which can cause breeding problems among swine.
"About the only thing you can do is just remove the source of grain that is contaminated or dilute it down to a subtoxic level," Dr. Hicks said.
Toxicologists he has consulted are "not very enthusiastic" about the effectiveness of commercial products that claim to have toxin-binding abilities.
Dr. Hicks thinks, however, most people working in the swine industry are aware of the risks posed by mycotoxins, particularly this year. He said it would be useful for veterinarians who do not perform much food animal work to have information on the most common mold toxins in grain, toxic concentrations of those substances, and the cost and availability of tests for mycotoxins.
People who are buying grain are working diligently to find corn that is unlikely to contain high amounts of mycotoxins, Dr. Ensley said. Producers are usually able to separate grain by quality and feed lower-quality grain to animals less likely to experience health problems from mycotoxins, but he does not know whether they will be able to do the same this year.
"This year, with the number of positives being so much higher and the concentrations being so much higher, we anticipate seeing more problems," Dr. Ensley said. "But at this point, I'd say I've just had a handful of people that felt like they had feed refusal or feed efficiency issues so far with 2009 grain—and mostly in pigs."
Livestock producers are intent on assessing mycotoxin concentration and keeping high concentrations out of the diets of swine, which are more sensitive to mycotoxin poisoning than ruminants are, Dr. Ensley said.
Dr. Ensley said it is unclear how effectively commercial products intended to reduce the impacts of mycotoxins can be used in response to mycotoxin poisoning, particularly with high concentrations of the toxins.
"Just don't assume that, if you're going to use a binder, you're going to be able to eliminate all problems associated with mycotoxins," Dr. Ensley said.
Dr. Garrett R. Oetzel, an associate professor of food animal production medicine at the University of Wisconsin-Madison, said mycotoxin assays are more expensive, but more useful, than yeast and mold counts in testing feed of suspect quality.
"It's likely not the mold itself that causes problems but the mycotoxins that could be produced by those molds," Dr. Oetzel said. "And we do know from experience that mold counts are not very well-correlated with actual mycotoxin levels in the feed.
"There's quite the temptation to do a yeast and mold count, but we would be much better off to do a mycotoxin screen to see if these compounds are present and might interfere with animal health," Dr. Oetzel said.
While quick yeast and mold counts are available for about $15 a sample, Dr. Oetzel said testing for an array of mycotoxins could cost $30 to hundreds of dollars per sample. Typical mycotoxin screenings likely cost about $75, he said.
Data on acceptable mycotoxin levels vary among studies, but these studies do provide some information on substances that are detrimental to livestock, he said.
Dr. Oetzel does not recommend routine mycotoxin screening, and he said feed evaluation typically starts with easier tests. Producers can check for increased heat on feed or visible mold, and Midwestern dairy farmers, for example, can monitor the response among animals when they add or remove suspect feed from mixed rations.
Aflatoxins, which FDA information indicates are most common in warm, humid regions of the south and central U.S., are known human carcinogens and regulated substances that require additional precautions.
Tolerances for mycotoxins and clinical signs of mycotoxin poisoning vary among animal species. The Food and Drug Administration has information on mycotoxin tolerances and action, guidance, and advisory concentrations at www.fda.gov/animalveterinary. Click on "Products," then on "Animal Food and Feeds," then on "Contaminants," and scroll down to "Mycotoxins in Feeds: CVM's Perspective."