More and more cattle producers are using fall and winter grazing to extend the grazing season, and for good reason. This management practice is a cost-effective option that reduces labour requirements and can keep livestock out of the corrals until just before calving season. Maximizing forage yield while maintaining forage quality is the goal for most producers. However, one area that is commonly overlooked is that of plant disease and the effects that mycotoxins can have on grazing livestock.
Crop disease is largely dependent on the weather conditions and for that reason it is very hard to manage. Cool and moist conditions when cereal crops were flowering has resulted in an increase of crop disease, particularly fusarium and ergot. Mycotoxins can be quite harmful to livestock, and while ruminants are generally more tolerant to mycotoxins than other livestock species, they are still at risk.
Fusarium will produce a several different toxins, including vomitoxin, zearalenone, and fumonisins. Each of these toxins will cause negative effects on beef cattle if present in high enough concentrations. The effects of each compound differ slightly but can be characterized by a reduction in feed intake, reduced growth and performance, suppressed immunity, and potential fertility issues such as disrupted breeding cycles and abortion. If any of these toxins are at levels of 5 ppm or higher, feeding management is necessary to avoid possible toxicity. It is important to note that straw from fusarium infected cereal crops will also contain the associated mycotoxins and can become an issue if cattle are consuming it.
When fusarium is present, it is more likely that other mould metabolites may also be present in Western Canadian cereal crops, for example aflatoxin and ochratoxin. These toxins can become more concentrated in stored feed, especially if moisture levels are elevated. Cattle consuming feed with aflatoxin may develop a suppressed immunity which could cause vaccines to fail. Moderate levels of ochratoxin can be broken down in the rumen and is of lesser concern for healthy cattle. However, it is a suspected carcinogen and can lead to liver and kidney damage, as well as abortions, if large amounts are consumed.
The incidence of ergot has been steadily increasing in recent years, and this year is no different. Most cereal crops and grass species are susceptible to ergot and for this reason both grain and forages should be considered for possible infection. Very few ergot bodies are needed to harm livestock as deaths related to ergot poisoning have been observed with as little as 0.04% in the diet by weight. Symptoms include depressed feed intake, reduced milk production, lack of blood flow to extremities resulting in the loss of ears, tails, and hooves, and eventually death.
If conditions remain wet through the fall, forage set aside for fall grazing will be more likely to become mouldy. This is especially true for crops lying in the field destined for swath grazing, although standing forage, hay and green feed should not be overlooked. Producers should have their feed tested for mycotoxins if they suspect mould may be present. With the exception of ergot, contaminated feed can usually be diluted and fed provided a feed test is completed and mycotoxins levels are known, though feeding mouldy feedstuffs to pregnant cattle is not recommended.
Sean Thompson, BSc, AAg, Regional Livestock Specialist
Watrous regional office
For more information about winter feed management, contact your Regional Livestock Specialist, or call the Agriculture Knowledge Centre at 1-866-457-2377.
