The summer of 2012 has presented us a great deal of challenges. This fall’s crop will be characterized by lower than expected yields in many places as well as dryer than expected crops. These concerns could lead to quality and quantity issues when harvest high-moisture crops such as corn silage and earlage and even dry kernel corn.
Common issues regarding crop quality include molds and mycotoxins. Myotoxins in feedstuffs can reduce performance in cattle and can have detrimental effects on both finishing animals and reproducing males and females.
Aspergillus, an olive-green powdery mold, is favored by hot, dry conditions at pollination. These conditions were present in many areas this summer. Aspergillus begins to grow when corn moisture is around 32 percent, and will continue to grow until moisture drops below 15 percent.
Aspergillus itself is not the greatest concern. The greater concern occurs when Aspergillus fungi produce the mycotoxin aflatoxin. Aflatoxin growth is promoted with high temperatures during grain fill and pollination, and may also be promoted when high overnight temperatures (greater than 70 degrees) are present.
As kernel moisture decreases, aflatoxin production increases. Optimum aflatoxin growth occurs at 18-20 percent kernel moisture and stops at around 15 percent kernel moisture. If Aspergillus is a potential concern, producers should scout their fields at 5-10 locations throughout the field. If powdery-green molds are present on greater than 10 percent of the ears sampled, the field should be scheduled for immediate harvest and ears should be sent in to a testing laboratory for analyses.
If suspect feed is tested and aflatoxin concentration is below 200 parts-per-billion (ppb), the feed should be safe for all classes of cattle. At 200 ppb, calves may show reduced intake and weight gain, while adult cattle may not be affected until concentrations reach 500 ppb or greater.
These feeds can be utilized, but should be diluted so that aflatoxin concentrations do not exceed 20 ppb in the total ration for calves, 100 ppb for breeding cows, and 300 ppb for finishing cattle.
For the reproducing animals, the myotoxin zearalenone (ZEA) is also of concern. Zearalenone is produced by the fungus that causes gibberalla ear rot, Fusarium graminearum, and often co-exists with the myotoxin deoxynivalenol (DON), also known as vomitoxin. Zearalenone has many profound impacts on reproductive function due to its estrogenic actions.
Zearalenone competes with the naturally produced hormone estradiol-17‚ for binding sites (estradiol receptors) in various organs in the body of both males and females. Although the efficiency that ZEA will bind to the estrogen receptor is low (< 10 percent the affinity), it can interfere with normal reproductive functions. By mimicking the actions of estradiol, ZEA can cause estrogenic effects even when natural estradiol concentrations should be low.
Additionally, ZEA can obstruct normal steroid hormone (estradiol, testosterone, progesterone) synthesis in the ovaries and testicles of livestock.
Prolonged exposure to ZEA through consumption of contaminated feed is a concern in heifers. Effects of extended exposure to ZEA may be similar to the effects of implanting heifers at birth or at weaning with estrogenic implants and may negatively impact subsequent reproductive function.
Beef and dairy producers should be cautious when feeding ZEA-contaminated corn (5+ ppm) to developing heifers, since the estrogenic activity of ZEA can compromise normal endocrine function and uterine development. Heifers consuming as little as 1.5 ppm of ZEA in the feed have exhibited swelling of the mammary gland and increased incidences of vagintitis.
This would also include creep rations for beef calves. In females during the breeding season, ZEA concentrations greater than 10 ppm in the feed can result in failure to conceive and increased incidences of abortions. Diets of non-lactating cows in late gestation should not contain more than 20 ppm of ZEA.
If you are concerned your feedstuffs may be contaminated with a mycotoxin and/or animal are exhibiting aliments associated with mycotoxins contact your nutritionist or extension specialist. They can provide additional information on handling feeds that may be infected with aflatoxin or zearalenone.
For more information on this and other beef-related topics, visit the University of Minnesota Beef Team website at www.extension.umn.edu/beef.