The variety of ingredients in a ruminant diet, including cereals, protein feed, forages, legumes, sorghum etc., exposes dairy cows to a wide range of contaminants at different dosages and at different times. Mycotoxins—fungal metabolites toxic to animals and humans produced by common molds found in almost all types of grains—can cause significant damage to animal health, performance and productivity. Furthermore, some mycotoxins can be carried over from ingested feed into animals’ milk, such as the case with aflatoxins.
The 2015 BIOMIN Mycotoxin Survey covers agricultural commodity samples from over 60 countries to identify the presence and potential risk posed to livestock animal production by mycotoxins worldwide. Corn silage samples were tested for aflatoxins (Afla), zearalenone (ZEN), deoxynivalenol (DON), T-2 toxin (T-2), fumonisins (FUM) and ochratoxin A (OTA). Figure 1 shows the prevalence of six major mycotoxins in corn silage. More than 40% of samples tested positive for DON at concentrations above the recommended threshold for cows. Nearly one out of four samples had ZEN ppb levels in excess of recommendations. Likewise, Afla exceeded the risk threshold 11% of the time.
Table 1 provides further details on the number of samples, average and maximum concentration levels, and recommended maximum thresholds for dairy cows.
Figure 1. 2015 BIOMIN Mycotoxin Survey results for corn silage. Bars represent percentage of positive samples. Dots display the occurrence of mycotoxins above risk threshold levels (bottom row, Table 1).
Table 1. Corn silage results, 2015 BIOMIN Mycotoxin Survey.
Consequences for cows
Aflatoxins, produced by Aspergillus, are commonly found at low dosage in forages such as maize silage and hay. It has been shown to carry-over into milk and pose a threat to humans upon ingestion—a key reason for regulatory maximum levels in milk in many jurisdictions. Aflatoxins are associated with impaired rumen function, impaired udder health, increased somatic cell count, decreased resistance to environmental and microbial stressors and increased susceptibility to diseases. Even low doses can have serious health implications in the long-term.
Due to its estrogenic proprieties, zearalenone (ZEN) can impair reproduction and have nefarious effects on the reproductive cycle and estrogen hormone regulation in heifers and calves. In the rumen ZEN is converted into two forms: α- and β-zearalenol. The a-form is even more estrogenic, and hence potentially more disruptive to reproduction, than ZEN itself.
Deoxynivalenol (DON) is the most common mycotoxin in forages, occurring worldwide sometimes at high concentrations. It is associated with impaired rumen function, diarrhea, metabolic disorders, mastitis, metritis and lameness.