When it comes to feed quality, we usually think in terms of nutritional properties such as energy, protein or mineral content. There are, however, other feed characteristics that have an impact on quality, one of which is mycotoxin contamination. Depending on crop type, environment, location, harvest and storage management, there are a wide variety of mycotoxins that can potentially contaminate the feed supply. Examples include ergot alkaloids in rye, deoxynivalenol in wheat and barley and alfatoxin in corn. These mycotoxins result from fungal infections of plants and develop as the plant matures and/or during storage. Symptoms of mycotoxin poisoning include decreased feed intake and growth, reduced milk production, and increased morbidity and mortality in calves as well as adult cattle.
Mycotoxin contaminated feed is not a new issue. However, if we use the last few growing seasons as a yardstick, it appears that the extent of the problem is increasing, particularly for Central and Western Canada. The re-emergence of this issue has been attributed to a number of factors including favourable environmental conditions in the spring and the emergence of more aggressive fungal strains contaminating today’s crops. In the August 2014 issue of Canadian Cattlemen, Dr. Reynold Bergen addressed concerns with ergot. In this column, I will focus on fusarium contamination of wheat and other cereals and the implications for your feeding program.
Fusarium infection of wheat, barley and corn results in a plant disease known as fusarium head blight (FHB). This disease of cereals has been established in Central Canada for several decades and is slowly moving westward. This fall, for example, there are a numerous reports throughout Manitoba and Saskatchewan of FHB contamination of winter wheat, durum and Hard Red Spring wheat. In cereals such as wheat, FHB targets the seed head and results in shrunken, off-colour kernels, known as fusarium-damaged kernels (FDK) or more commonly “tombstones.” In corn it is sometimes referred to as pink ear rot. For the grain producer, crop yield, quality and end use can be negatively affected. For livestock producers, the issue is mycotoxin contamination.
Fusarium-damaged kernels can be contaminated with a number of mycotoxins that collectively are called the trichothecenes. Included in this group are deoxynivalenol (DON), nivalenol, T-2 and HT-2 toxins. The specific mycotoxin or combination of mycotoxins found in contaminated grain depends on the fusarium species that infected the plant. For example, infection by fusarium graminearum will result in the production of DON as well as a number of DON-like derivatives. Under certain conditions, it can also produce T-2 toxin.
Toxins such as T-2 and HT-2 are potent protein inhibitors whose ingestion at levels as low as one part per million (ppm) can result in issues with reduced feed intake, poor growth, ulceration and hemorrhaging of the digestive tract, and even death. Canadian Food Inspection Agency (CFIA) guidelines for cattle limit the intake of HT-2 toxin to 0.1 ppm while the recommended tolerance level for T-2 toxin is less than one ppm (DM basis).
Deoxynivalenol, while not as potent as T-2 or HT-2 toxin, is the most common mycotoxin encountered in fusarium-contaminated grain. Deoxynivalenol is commonly called vomitoxin due to the fact that pigs exhibit severe feed refusal and vomiting at very low levels of intake. Fortunately, cattle are less sensitive, likely due to degradation of DON by rumen bacteria. Reduced feed intake and growth and poor immune function are the major issues associated with feeding DON-contaminated grain to cattle. The upper dietary inclusion limit for DON is not as clear-cut as it is with other mycotoxins. The CFIA guideline for DON in the diet of beef cattle is a maximum of five ppm. For pregnant heifers or cows, this is a reasonable guideline. However, for growing and finishing cattle, it may be on the low side. A Manitoba Agriculture factsheet from the 1990s summarized a number of DON-related research trials which demonstrated that DON levels at nine ppm in backgrounding diets and as high as 18 ppm in finishing diets did not negatively influence growth, feed intake or feed efficiency.
One issue to consider when feeding DON-contaminated grain is that the presence of DON can be a warning sign that other mycotoxins are also present. For example, I have seen test results from 2014 wheat samples that showed DON at 2.5 ppm and HT-2 toxin at 1.3 ppm. Similarly a wheat screening sample containing 11 ppm DON had a combined total of 2.5 ppm for HT-2 and T-2 toxins. Not a lot is known about the combined effects of these mycotoxins, in some cases they may act in a synergistic fashion increasing the negative effects of one or more of these mycotoxins. In such situations, caution is advised, even if one is blending the contaminated grain to “safe” levels.
There are a several laboratories that offer testing services for mycotoxins in grain and forage samples. If you suspect issues, have your feed tested prior to purchase and/or feeding. For larger operations receiving grain on a regular basis, work with your nutritionist to set up a purchasing protocol that sets limits to the level of ergot or fusarium contamination that you will accept.