November 19, 2004
Poor Corn Crop Concerns Livestock Producers
The weather’s impact on North Dakota corn crops this year has livestock producers concerned about using corn for pasture grazing livestock, particularly beef cows.
Summer and early fall 2004 was wet and unusually cool in most of the state. Frosts occurred in early June and on Aug. 19-20, resulting in thousands of acres of corn that did not reach maturity. Besides some potential problems of grain overload and acidosis, the major question is whether moldy corn will cause problems with pregnant beef cows.
The safest response is not to feed moldy feedstuffs to livestock, according to a North Dakota State University Extension Service beef specialist, plant pathologist and veterinarian. Molds or fungi can release mold spores that can cause lung irritation. Pregnant cows fed and/or bedded on moldy vegetation potentially are susceptible to mold infections (particularly Aspergillus mold infections) that can result in mycotic abortions.
More importantly, molds may produce secondary chemicals or mycotoxins that can result in a variety of harmful effects in animals, said beef specialist Greg Lardy, plant pathologist Marcia McMullen and veterinarian Charles Stoltenow. Some of the more common mycotoxins can be tested for in feed, but other mycotoxins have not been well identified and are not included in toxin analyses of corn.
Sampling standing corn is a difficult process, the Extension specialists said. Molds and mycotoxins generally grow sporadically throughout a field, with some areas of clean corn and other areas of high mold and mycotoxins or ‘hot spots.’ Take ear corn from several areas of the field and the laboratory can subsample it for testing.
This year, the appearance of black molds on the stalk, husks and corn is very common. Typically, the molds responsible for the black discoloration are Cladosporium, Rhizopus and Alternaria. These molds are not recognized as being contributors to mycotoxin problems in livestock. However, with the moisture content of grain at greater than 14 percent and alternating warmer days and cooler nights, a succession of different molds can grow on the corn. The presence of Fusarium molds causing pinkish discoloration to stalks and corn (“pink ear rot”) and some whitish mold growth are a big concern.
The Fusarium molds are known producers of mycotoxins, particularly the trichothecene mycotoxins, that affect livestock. Generally, ruminants can break down some of these Fusarium mycotoxins within the rumen and have few clinical problems. However, when mycotoxins are in high concentrations or multiple mycotoxins are present, particularly the more toxic compounds, ruminants can develop clinical signs (see accompanying table).
This year, the Veterinary Diagnostic Lab at NDSU has been testing ear corn samples for about 17 common Fusarium mycotoxins. Results ranged from no detectable mycotoxins to low levels of vomitoxin or DON (deoxynivalenol) and zearalenone to finding some very toxic mycotoxins, theT-2 and HT-2 toxins. These mycotoxins are very stable compounds and will remain in the corn even after it has undergone ensiling.
Tests also have detected aflatoxins, but at very low levels. The U.S. Food and Drug Administration set the upper level for aflatoxins in foods for pregnant cattle at 100 parts per billion. Aflatoxin production requires a very warm growing season, which wasn’t present in North Dakota’s corn production areas. Therefore, aflatoxins should not be a concern when considering whether to graze damaged corn fields, the Extension specialists and veterinarian said.
If moldy corn has to be used for cattle grazing, examine the corn periodically to check for any pinkish or whitish mold growth, which can indicate Fusarium molds. The NDSU Veterinary Diagnostic Laboratory representative can test samples of ear corn for mycotoxins. Some laboratories use mold or yeast spore counts to indicate moldy, deteriorated feed. However, a mold count does not identify the type of mold (e.g., Cladosporium, Rhizopus, Fusarium) or whether any mycotoxins are present and at what level.
To reduce the potential problems, limit or dilute the cattle’s exposure to moldy feed by feeding additional nonmoldy hay or grain, the specialists and veterinarian advise. More importantly, check the cattle periodically.
Clinical signs of mycotoxin exposure include lack of appetite, weight loss, skin or muzzle irritation/ulcers and diarrhea, as well as bloody diarrhea, poor response to antibiotic treatment, and in some cases, abortions. If producers observe problems, they should stop exposing their cattle to the moldy feed and consult their local veterinarian. These problems are not exclusive to moldy feed, but could indicate possible mold involvement.
For more information, contact Lardy at (701) 231-7660, McMullen at (701) 231-7627 or Stoltenow at (701) 231-7522. For questions about testing, call Michelle Mostrom, NDSU Veterinary Diagnostic Laboratory toxicologist, at (701) 231-8307. The cost of a trichothecene mycotoxin screen for North Dakota producers is $50, with about a three- to four-day turnaround for mycotoxin analyses of ear corn.
Greg Lardy, 231-7660, firstname.lastname@example.org;
here for a printable PDF version of this graphic. (8 Kb b&w table)