by Katie Raver, M.S. Dairy Technical Services Manager and Kai Yuan, Ph.D. Senior Research and Technical Advisor
Mycotoxins have been a concern to dairy producers for many years due to the large economic impact they have on the industry. Losses are attributed to lower production coupled with potential health events. There is also often a cost associated with feed changes to help mitigate some negative impacts.
What are mycotoxins? Well, molds need nutrients to grow and they compete with the host plant for nutrients. Some research has shown that in order to gain a competitive advantage, the mold produces a toxin. Mycotoxin production is likely to be greatest when plant demand for nutrients is highest or when nutrient availability is limited. Mycotoxins can have many negative impacts on the cows including decreased feed intake, ruminal upset, decreased milk efficiency, poor reproductive performance, and reduced immunity.
When are mycotoxins produced? The production of mycotoxins can occur either pre-harvest due to crop growth conditions, or post-harvest due to feed contamination and poor ensiling processes. During the growing season, stress ranging from drought to pest infestation can increase the risk of disease. One of the biggest risk factors in a plant developing a fungal infection is mechanical damage to the physical barriers that would normally protect it. This year’s growing season has presented many challenges in all different areas across the nation, and thus could predispose the feed to having more toxin challenges. Many parts of the country saw cooler wet conditions to start out with, while others saw extreme heat and drought. Wet conditions can favor the production of Fusarium spp. while drought can favor the production of Aspergillus spp. in the field. Field prevention methods include a balanced soil fertility program, crop rotation, fungicide application, and timely harvest.
A balanced soil fertility program reduces plant stress and plant diseases. For example, either excess or low amounts N can increase stalk rot incidence. Low soil K can also increase the risk of stalk rot and production of mycotoxins. QLF carbon-based agronomy products along side a balanced fertility program can increase nutrient uptake in plants from soil and can help lower plant stress.
Corn residue that remains on the soil surface offers a host that can produce mold spores for the subsequent crop. Therefore, crop rotation to a non-susceptible crop is important.
Fungi that cause leaf diseases in corn may indirectly impact the potential for mold and mycotoxin development in other plant parts. Controlling fungi diseases may prevent mycotoxin development.
A timely harvest to get the crop out of the field is extremely important. During the fall when temperatures alternate between 45 to 75 degrees, it is optimal for Fusarium mold and mycotoxin to develop. Therefore, the longer the crop stands in the field, the more opportunity for mold and mycotoxin development.
Storage of ensiled feeds
Use of oxygen barrier film on bunkers or piles helps exclude air, reduces surface spoilage, and minimizes precipitation runoff contact with the silage. Monitor water drainage and minimize water infiltration around silage piles, bunkers, and bag storage areas after rainfall and during snowmelt. Good sanitation around silage piles, bunkers, and bags discourages pest damage to plastic covers and bags to help maintain an oxygen-free environment around the silage.
It is important to note that even though visual signs of mold may not be present on the plant mycotoxins may still be present. If a crop is thought to have fungal diseases and possible mycotoxin contamination, proper ensiling conditions are critical to decrease toxin production after harvest. Nevertheless, this cannot eliminate already present toxins. Care should be taken to make sure silage is packed properly to minimize the presence of oxygen within the silage, because most fungi cannot survive in anaerobic conditions. A rapid decrease in the pH of the ensiled crop can also help to decrease the amount of toxins, as most of the fungi are intolerant of low pH. The top layers of silage oftentimes are at the most risk as they typically have more chance of air exposure. Not feeding the top layer may help decrease the incidence of mycotoxin related health events. Manage silage bunker and pile faces carefully, as well as daily usage rates to minimize air entry and secondary fermentation. Laboratory analyses of molds, mycotoxins, and yeasts are available for at-risk feeds are recommended before feedout. If the test does show presence of toxins, there are several additives that can be used to help mitigate the negative impacts of the toxins. Follow FDA guidelines and safety recommendations for mycotoxin-containing feeds.
Table 1: Common toxins, favorable conditions of development, and animal health concerns.
|Fungi||Common Toxins Produced||Favorable Conditions||Animal Health Concerns|
|Fusarium||Trichothecenes A, (T2, HT-2), Trichothecenes B (DON),
|Field: High humidity, high temperature fluctuation (Cool, wet conditions)
Ensiling: growth unfavorable due to silage pH, however toxins are not completely destroyed in ensiling
|Gastroenteritis, intestinal hemorrhages, reduction in performance, reproductive problems, reduced protein flow to duodenum, altered rumen fermentation|
|Aspergillus Flavus||Aflatoxins||Field: High temperature, high humidity, drought stress, insect pressure; presents as a kernel infection
Ensiling: Aerobic conditions can increase toxin production, toxin can persist through ensiling
|Reduced milk production, decreased efficiency, Liver malfunction, depression of ruminal function
** FDA regulated for carryover into milk and possible carcinogenic effects
|Aspergillus (other)||Gliotoxin, Ochratoxin||Field: Hot, dry conditions
Ensiling: improper DM of silage, high silage pH, improper storage conditions, air exposure
|Decrease in reproductive performance, immune suppression, hemorrhagic bowel syndrome|
Adapted from Ogunade et al 2018