by Tamara Scully
Mycotoxin pressures have been high with this fall’s grain harvest, leading to concern across much of the Eastern Seaboard. Drought stress, followed by heavy rains, set the season up to be one in which molds, and therefore mycotoxins, became a serious concern. Random sampling of corn silage by Alltech scientists resulted in more than 75 percent of corn silage samples having mycotoxin levels considered moderate or high for dairy feed.
Mycotoxins are “the actual chemical compounds that the molds produce,” Dr. Alexandra Weaver, of the Alltech Mycotoxin Management Team explained during a presentation at the 2018 Penn State Dairy Cattle Nutrition Workshop.
It’s not always clear-cut as to whether these mycotoxins originated in the field, or in grain storage. Wet weather in the field is a major factor in whether or not mycotoxin development is favored, but storage of grains can add to the risk that mycotoxins can grow and proliferate.
One mycotoxin commonly found is the “vomitoxin” or deoxynivalenol. Zearalenone is a by-product of fusarium, too, and causes estrogenic responses. Aspergillus is another concern, and normally proliferates during storage. It has been found, however, in newly harvested crops this season, Weaver cautioned. Penicillium molds are also commonly found in feed. With very specific parameters for controlling the amount of mycotoxins in feed, quantitative laboratory tests which measure the contamination are needed.
“We can’t tell, just visibly, whether we have mycotoxins or not,” she explained.
Mycotoxins are often found together, meaning that contaminated feed usually has more than one pathogen present. And these pathogens have a synergistic effect, causing greater health issues and performance losses in the herd. The additive effect means that “one plus one equals 10,” Weaver said.
While a high level of mycotoxins can cause an acute reaction, it is the cumulative effect of low-level consumption that compromises herd health and productivity. Chronic mycotoxin exposure causes concerns throughout the life span of the cow, affecting reproduction, milk production, rumen function and the immune system. Depending on the life stage of the animal, the impacts of mycotoxins can vary.
“There’s a lot of different systems that can be impacted by the mycotoxins,” Weaver said. “You want to maximize their genetic potential. Are mycotoxins influencing their potential?”
In calves, the presence of mycotoxins can cause rumen lesions and decrease the height of the rumen papillae, impacting digestion. Mycotoxins can change the IgA in colostrum, so calves are not receiving the full benefits of colostrum they need from their mothers.
Gut health is linked to immunity. While outward signs may not be present, changes in the calf intestinal tract due to mycotoxin presence leave it more susceptible to Escherichia coli infection, too. Growth is impacted, and there is a negative impact on breeding ability as well.
With all of the stressors calves are experiencing, the detrimental effects of mycotoxin are “just adding to the total problems,” she said.
Heifers exposed to mycotoxins experience slowed growth and delayed puberty. There are immune system changes, and organs are impacted. Genetic potential can be decreased, perhaps as much as 25 percent or more. Breeding cows experience abortion, endometritis, and increased hyperketonemia, and take longer to get pregnant when mycotoxins are present. Smaller calf birthweight and decreased gestation length are also believed to be influenced by the presence of mycotoxins.
Additional stressors can greatly impact the cow and the calf during the stressful transition phase. At parturition, immune function is further stressed when mycotoxins are present. Immunoglobulin levels are suppressed by mycotoxins, and macrophage proliferation is decreased.
The milking herd is exposed to many demands. Adding mycotoxins to the mix can alter the milk component composition, decreasing the percentage of milk fat. Gut lesions from mycotoxins can change the ability to absorb nutrients. Rumen lesions can decrease feed intake. A decrease in total volatile fatty acids levels is also an effect of mycotoxins, and changes rumen functioning. Changes in the endocrine system also occur.
Even at low levels of mycotoxin exposure, 0.5ppm, milk production starts to decrease. In one study, data from three farms showed that cows had a 62 percent increase in somatic cell counts when consuming mycotoxins alone, resulting in a suppression of more than 13.2 lbs. of milk per cow, per day.
Alltech has a calculator which allows producers to estimate the performance changes they would see in their herds if they encounter a mycotoxin risk. This calculator is sensitive enough to predict slight changes that a farmer “might not notice on a daily basis,” Weaver said, and can help producers to better understand the economic impact of mycotoxins on the dairy’s profitability.
Minimizing risks from mycotoxins occurs from the field to the feed bunk. Crop rotation, tillage management, soil fertility and chemical or biological control of insects and diseases all play a role. The harvest environment, including proper equipment settings, as well as the storage environment also affect the outcome. Packing the bunk and feeding properly from the bunk, to reduce the exposure of the feed to oxygen, reduces the risk of mycotoxin development.
Mycotoxin presence in the dairy herd affects cows at every stage of their life. The negative impact on cow health, productivity and genetic potential have economic consequences. Mitigating the risk along every step of the feed chain can have long-term benefits.
“Low levels can be having an impact. That certainly adds up over time,” Weaver concluded. “Mycotoxins aren’t really a question of if you have a challenge, but how much of a challenge you have.”