Aflatoxins in Feed and Milk
By Sally Flis, Ph.D. - Feed and Crop Support Specialist
Stressful growing conditions and pest pressure can increase the potential for the growth of molds on corn ears. Aflatoxin B1 (AFB1) is of primary concern because it is highly toxic and can be carcinogenic. The concentration of AFB1 in dairy diets is limited to 20 parts per billion (ppb). Feed contaminated with AFB1 can result in milk contaminated with Aflatoxin M1 (AFM1). The AFB1 is metabolized to AFM1 and 1 to 3% of the concentration in the feed will show up in the milk. Milk leaving the farm is regularly tested for AFM1 concentration and milk above 0.5 ppb is not accepted for processing for human consumption.
Where does AFB1 come from?
An olive green colored mold (Aspergillus flavus) that grows on the ears of corn is responsible for the production of AFB1. Ideal conditions for mold growth occur when temperatures are between 80° to 100° F with high humidity and high night temperatures during ear fill and pollination. Pest damage to the husks makes it even easier for the mold to infect the grain. Not all ear mold growth is from Aspergillus flavus as there are hundreds of other mold and mycotoxins that can grow on corn. If your growing conditions are a concern for the growth of mold on corn ears, scouting your fields before harvest can help you identify the fields that need to be tested. Testing prior to harvest can be difficult, but contaminated feed will be easiest to manage if stored separately.
Aflatoxin Levels
The mycotoxin panel that is available from the Dairy One Forage Lab includes AFB1. Over the last 4 growing seasons the lab has reported a wide range of AFB1 concentrations (Table 1). The large range is influenced by growing conditions for each season and the diverse geography covered by Dairy One.
Table 1. Aflatoxin B1 concentration in corn silage tested
in the Dairy One Forage Lab
|
Year
|
Average AFB1, ppb
|
Pounds
DM of Feed Allowable*
|
High AFB1, ppb
|
Pounds
DM of Feed Allowable*
|
n
|
|
May 2015 - April 2016
|
0.25
|
79.6
|
2.01
|
9.9
|
205
|
|
May 2014 - April 2015
|
0.09
|
221
|
0.82
|
24.3
|
190
|
|
May 2013 - April 2014
|
2.38
|
8.4
|
13.3
|
1.5
|
252
|
|
May 2012 - April 2013
|
1.25
|
15.9
|
6.98
|
2.9
|
454
|
*Pounds of corn silage in the diet that keep the AFB1 concentration below 20 ppb.
Ration balancing software has the ability to accept AFB1 concentrations and keep a tally of total AFB1 concentration in the ration. With a limit of 20 ppb in a ration, even moderate concentrations of AFB1 can limit your ability to feed contaminated corn silage (Table 1).
Corn silage is not the only source of AFB1 in diets. If you are having AFM1 contamination problems in your milk, test all corn based feeds. Distiller's grains and corn gluten feed may also be contaminated as the mycotoxins are not destroyed during processing. Mycotoxin testing can be expensive, but milk above the 0.5 ppb level will not be accepted by processors and the farm will not able to ship milk until it tests below 0.5 ppb. When contaminated feed is used on farm the AFM1 can show up in the milk within hours of feeding, but can take days to disappear.
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