Vomitoxin: How much is too much in dairy diets?

By Rod Martin
This year’s weather conditions have been conducive to the development of vomitoxin in wheat.   The price for this wheat grain can be significantly discounted depending on the contamination level.  Consequently, dairy producers are asking how they can feed wheat grain in their dairy diets without incurring negative production and health effects.

Furthermore, wheat straw is likely to have vomitoxin contamination if the grain tests high.  Producers need to be aware of this as wheat straw is commonly fed at relatively high levels in dry cow and fresh cow diets.  It may also be used in lactation diets, but to a lesser extent.

Vomitoxin contamination is caused by a Fusarium mold.  Swine are most susceptible to this toxin and current recommendations suggest an upper limit of 1 ppm of the total diet dry matter for hogs.

Dairy cattle are less susceptible to vomitoxin and current guidelines suggest an upper limit of 5 ppm in the total diet dry matter.  However, some recommendations suggest the upper limit should be in the 2- to 3-ppm range.  Click here for a list of mycotoxin guidelines.

Keep in mind, the presence of vomitoxin in feeds may also indicate the presence of other mycotoxins.  Weather conditions conducive to vomitoxin production are also conducive to other mycotoxins that may cause production and health issues.

Before feeding any potentially contaminated wheat grain and/or wheat straw, sample the product to determine the contamination level.  We have seen vomitoxin levels as high as 12 to 16 ppm in both wheat grain and straw.  Once you know the contamination level, you can determine how much you can feed before you reach the upper vomitoxin limit in your dairy diets.

Typically, ground wheat is fed at a 3- to 5-pound feeding rate as long as other starch sources in the diet are not highly soluble in the rumen.  For example, a diet containing 3 to 5 pounds of ground wheat dry matter with finely ground dry corn along with a 60-percent corn silage and 40-percent haylage makes sense.  In contrast, a diet with 3 to 5 pounds of ground wheat in combination with wet high moisture corn and 80-percent corn silage is problematic due to high levels of soluble starch in the rumen.

Let’s use an example.  You decide to feed 3.5 pounds of dry matter from wheat and you know the vomitoxin level is 10 ppm.  This means that 6.6 percent of the diet dry matter is from wheat (3.5 pounds wheat / 53 pounds dry matter intake (DMI)).  Multiply that by 10 ppm and you find a 0.66-ppm contribution of vomitoxin from wheat.  The total diet should be less than 5 ppm vomitoxin.  Thus, as long as the rest of your feedstuffs are clean or have minimal vomitoxin, you should be fine.  However, to be on the safe side, you can send in a sample of the complete TMR to determine the final vomitoxin level.

Since wheat straw is proportionally fed at a higher rate in dry cow and transition diets, it is also important to run a wheat straw analysis to determine the vomitoxin level.

Let’s use another example following the same logic as above.  You determine that you have 8 ppm of vomitoxin in the straw and you are feeding 6 pounds of straw diet dry matter.  The straw would contribute 1.70 ppm of vomitoxin to the total diet ((6 pounds / 28 pounds DMI) x 8 ppm = 1.7 ppm).   If the dietary threshold is 5 ppm, you should be fine as long as the other feeds in the dry cow ration are clean.  But again, to be on the safe side, you can always test the complete TMR to see what the final vomitoxin number looks like.

In summary, test susceptible feeds for vomitoxin and work closely with your nutritionist to make sure you are not reaching the vomitoxin threshold in your diets.  Even though it is tough to determine if higher levels of vomitoxin are actually problematic in dairy herds, it just makes good sense to not push the envelope and stay within the current recommended guidelines.

About the author: Rod Martin is a dairy specialist and a member of the Vita Plus dairy technical services team.  He grew up on his family’s diversified livestock farm in southwest Wisconsin and attended the University of Wisconsin-Madison, where he earned a bachelor’s degree in agricultural education and animal science, and a master’s degree in animal nutrition.  He has 24 years of experience in consulting with Midwest dairy operations.