Recently, I walked with a beef producer into a hayfield cut a few days earlier and since had been rained on a couple of times. When I lifted a swath in the middle of the field the hay was dark brown on top and still green underneath. The producer said he was going to bale it tough that afternoon, because the weather forecast called for rain that evening. It wouldn’t surprise me if these bales will be mouldy when he cuts them open these bales this winter.
That shock on a cold winter morning should remind us: moulds/mycotoxins found in forage, grain and feed byproducts are a constant threat to beef cattle health and performance. As a result, people should learn the types and effects of specific moulds/mycotoxins that affect beef cattle, and sample and test suspect feed. If warranted, corrective action can be taken.
Not very palatable
One of the first lessons I learned is mouldy feeds are unpalatable to cattle. They often contain substantial mould levels with lower feed digestibility and reduce overall nutrient content. At their worst, a variety of moulds/mycotoxins cause mycosis (fungal infections) or cause mycotoxicosis, which encompass abnormal metabolism, damage organs, infertility and literarily can shut down the cattle’s entire immune system.
Of the many moulds in nature, three major ones pose the greatest beef feed threat. Aspergillus fluavus produces aflatoxins, fusarium moulds produce vomitoxin and zearalenone, and penicillium fungi produce related penicillium mycotoxins.
Our Prairie climate does not favour the growth of aspergillus moulds and therefore aflatoxins are of little threat to local home-grown forages, silages, and grains. This contaminate grows under high ambient temperatures coupled with high humidity and sometimes in drought conditions. The only real threat might be contained in dried distillers grains brought up from the southern United States.
Fusarium-derived mycotoxins are more of a threat to our livestock than aflatoxins, because fusarium moulds grow in cooler conditions. The fusarium mycotoxin deoxynivalenol (DON), commonly referred as vomitoxin, became widespread in Manitoba during the early 1990s, when a few years of cool summers and damp harvest weather favoured its growth in barley and wheat kernels. Since then it has spread to all three Prairie provinces.
Affect of mycotoxins
Field trials fed up to 66 ppm DON in dairy lactating rations did not result in significant adverse effects, aside from feeding lower grain quality and therefore feeding lower-energy dairy feed. Other research has shown one ppm DON reduces dry matter intake and disrupts feed digestibility, which led to a 1.5-2.0 kg drop in milk production. Some German work showed fusarium interferes with protein digestion in the rumen, which leads to higher ammonia levels.
However, zearalenone, another fusarium mycotoxin, mimics estrogen hormones can directly lead to infertility in beef cattle. Zearalenone-contaminated corn has been shown to cause erratic or silent heats, reduce conception rates and cause physical anomalies such as swollen and prolapsed vaginas, and spontaneous abortions. Furthermore, zearalenone causes liver damage and suppression of the immune system. Other fusarium mycotoxins such as T2 and fumonium will cause reproductive and health problems in cattle but are seldom found in our feedstuffs.
Unlike aflatoxins and fusarium mycotoxins, penicillium mycotoxins are a result of poorly stored feed or poor bunk management rather than challenging field conditions. They are not only suspect in causing reproductive problems in cattle, but also can hamper feed digestion.
One University of Minnesota experiment added graduated concentrations of patulin (a penicillium mycotoxin) to artificial fermenters containing rumen fluid collected from experimental cows. Researchers found the addition of patulin to these cultures significantly reduced organic matter, fibre and protein digestion of an added pelleted diet as well as depressed rumen microbe populations. Other studies show these mycotoxins can only be partially metabolized by rumen bugs.
Take it seriously
Luckily, most people are apprehensive when feeding visible mouldy feed to their beef cattle. However, they should realize not all mould contamination in forages, grain or protein concentrates are visible or consistent throughout individual bales or truckloads.
If a one or more feed ingredient (including the final beef diet) is suspected for mould, a mould-count test is recommended to conduct any initial investigation. This lab test counts the number of mould spores for any given feed sample. Mould count tests are inexpensive, but their information is also limited. They show the presence of mould, but fail to reveal the presence or extent of any mycotoxins.
Testing feed is a good thing, yet the final decision to feed mouldy feed to beef cattle comes down to common sense. The golden rule for me is to avoid feeding contaminated feed to beef cattle, especially to young calves, replacement heifers and pregnant cows. It’s that dangerous.