While the real time to start planning in order to minimize mycotoxin impacts is during hybrid seed selection, now is the next time to start identifying whether you may have challenges with this year’s feed.
During silage harvest, we have received a few pictures from around the state of Gibberella ear rot, which is the first sign that we may have Deoxynivalenol and Zearalenone in our corn silage this year.
The presence of Gibberella ear rot will tell you that there is a high likelihood of at least low levels of DON and ZEA but not what those levels will be. In order to know what the levels in your feed are, you may want to sample now to prepare and sample again at feed-out to know exactly what you are dealing with.
While DON levels stabilize after fermentation, levels can change during the first 60 days of fermentation, especially during the first 30 days. During this time, the fungus may continue to produce DON for a short time, but the form of DON changes from a less toxic, modified, masked form Deoxynivalenol 3-glucoside (D3G).
Deoxynivalenol 3-glucoside is formed when the plant detoxifies deoxynivalenol by attaching a glucose molecule to it; however, during fermentation or digestion, this glucose molecule can be removed, returning it to its more toxic form. Good storage practices, such as oxygen exclusion and high packing densities, can reduce the amount of DON that increases during the first 60 days of storage.
Unfortunately, knowing exactly what level of DON, ZEA or other mycotoxins will cause issues for your herd is challenging because they rarely appear alone; they often occur as a mycotoxin complex that affects your cows. Maximum dietary level recommendations vary by country, with Canada regulating DON levels for lactating dairy cows at 1 ppm while the U.S. recommends diets be below 5 ppm and Europe recommending less than 5 ppm.
Your diet and the rumen environment can also affect how efficiently the rumen can detoxify DON into Deep-deoxynivalenol (DOM-1), which is a derivative of DON that exhibits less toxicity to the intestinal barrier function. ZEA has minimal form change in a 6.8 pH rumen environment while levels increased under acidosis with a rumen pH of 5.8. Under this same rumen pH DON detoxification to DOM-1 also changed.
In a lactating rumen, the lower pH decreased DON levels more slowly than the higher pH. In Dry cows the low pH only reduced DON levels by about 30% while at a 6.8 pH most of the DON was converted in DOM-1 in 24 hours.
While DON often does not reduce milk production pounds, it can have many other adverse effects, including reducing milk protein levels. At the cellular level, including the rumen microbial level, it can inhibit protein synthesis. When DON binds to ribosomes during translation, it can cause a ribotoxic stress response that activates the expression of proinflammatory cytokines. DON causes oxidative stress in the liver, kidneys, lymphoid organs, intestines and in the mammary gland there was a reduction in alveolar cell proliferation. When DON is not fully degraded in the rumen and passes into the forestomach and intestines it can cause gut damage that increases bacterial translocation.
In some studies, long-term exposure has shown damage and reduced size in rumen epithelial cells. Overall, DON has been shown to reduce rumen pH, reduce protein production, lower cheese yield and firmness, alter rumen microflora, lower fiber digestibility, and increase somatic cell counts.
While DON can also alter reproduction, the bigger challenge for reproduction comes from ZEA, which is an estrogen-mimicking toxin. ZEA binds to estrogen receptors, interfering with animals’ reproductive function. Unlike DON, which the rumen detoxifies, one of the metabolites of ZEA is 60 times more potent, while the other is 0.2 times as potent. Diet levels as low as 0.3 mg/kg lowered oocyte quality in heifers, and other studies found inflammation in the reproductive tract and lower oocyte maturation.
The detoxification of DON and ZEA is different from that of other mycotoxins, as organoclays do not bind well to DON or ZEA. However, organic clay and the cell wall of green seaweed can reduce ZEA exposure when fed together. DON levels in diets are best managed through products that improve gut health and encourage the biotransformation to the less toxic metabolite DOM-1.
However, the rumen environment, such as pH and passage rate, can affect the efficacy of most products. Antioxidants and other feeding strategies that reduce inflammation and improve immune response can benefit high-DON diets.
(Jason Hartschuh is an assistant professor and field specialist in dairy management and precision livestock at Ohio State University Extension. He can be reached at hartschuh.11@osu.edu.)
