Last year’s weather was not particularly kind to growing corn on the eastern Prairies. A late spring planting, cold weather in July, and topped off by a cloudy fall created millions of bushels of corn that was not initially dry enough for storage.
Some of this wet corn was dried down and augered into a bin, much of it was also put up as high-moisture corn, and even a small portion was left out in the field until harvested earlier this year. Regardless of how this corn was eventually handled; mould (and mycotoxins) seem to hit this previous corn crop particularly hard. Without taking the necessary actions and precautions when it does occur, feeding mouldy corn to dairy cattle can be very dangerous.
Mould growth in corn can develop in a grain bin when grain moisture levels are above 14 per cent, the storage temperature is above freezing and the corn is exposed to air (oxygen). High-moisture grain corn also can be at risk for mould growth, if the moisture content of storage is incorrect (recommended at 25 to 28 per cent moisture for oxygen-limiting tower and 30 to 35 per cent moisture for ag-bags and bunks) or pH of the corn mass is not quickly stabilized to an acidic 4.5 by proper respiration (oxygen removal) and fermentation processes.
Three major moulds
Of the many moulds that can grow and proliferate in harvested corn due to improper storage conditions; three major moulds pose the greatest dairy cow threat with associated deadly mycotoxins are: Aspergillus fluavus that produce aflatoxins, Fusarium moulds that produce vomitoxin and zearalenone, and Penicillium fungi that produce related penicillium mycotoxins.
Most Canadian climates do not to favour the growth of Aspergillus fluavus and therefore Aflatoxins are of little threat to our dairy cattle. Fusarium-derived mycotoxins are more of a danger to our livestock than aflatoxins, because they grow in cooler conditions found in Western Canada.
Initially, it was thought fusarium-derived vomitoxin was toxic to dairy cattle, yet various field trials fed up to 66 ppm (parts per million) vomitoxin in dairy diets and most dairy cattle failed to exhibit any visible signs of reproductive or health problems. Most of these trials did show that once vomitoxin reached over three to five ppm in different tested grains; there was a detrimental effect upon respective grain bushel weight and resulted in lower-energy feed for lactating dairy cows.
In contrast, zearalenone, another fusarium mycotoxin has estrogen-like properties, which will cause infertility in dairy cattle. As little as 300 ppb (parts per billion) in the total dairy diet (dmi, basis) from z-contaminated corn has been implicated in disrupting heat cycles, reducing conception rates, causing visible symptoms such as swollen vulvas, and prolapsed vaginas, and spontaneous abortions. Furthermore, zearalenone can cause liver damage and has been shown to suppress the immune system in dairy cattle.
An honourable mention should be given to other fusarium mycotoxins such as T2 and fumonium that can cause reproductive and health problems in cattle but are seldom found in Canadian feedstuffs. Similarly, penicillium mycotoxins have also been linked to reproductive and health problems in dairy cattle.
No smoking gun
Unfortunately, without “the smoking gun” of large known amounts of mouldy corn consumed by ailing dairy cattle and causing direct negative effects, it is very difficult to many dairy producers to know that they might have a mouldy corn problem in the first place, for two major reasons.
First, mouldy corn kernels are often not uniformly distributed in a bin of corn, but are located in isolated pockets or along the bin walls. Even if a significant shot of mouldy corn goes into the total mixed ration (TMR) for dairy cows, most people may simply not notice as it gets hammered or rolled and then mixed along with the “good corn” in the TMR and become invisible anyway!
Secondly, symptoms of mould and mycotoxins poisoning in cattle is likely non-specific and often the result of a negative progression of health, reproductive and performance problems caused by the contamination. Even a post-mortem examination of a dead cow may yield inconclusive results, which could mistakenly be attributed to another cause such as malnutrition or disease.
If one suspects a mouldy corn problem on the farm such as: mouldy corn is seen coming out of bin or cows are off their feed/lack of cud-chewing/loose manure/substantial breeding problems after feeding suspect corn, it is a good idea to send a representative corn sample from the bin for laboratory mould testing.
Mould count tests are inexpensive, but their usefulness as sound information is limited, since most moulds are not poisonous and it says little about the presence of any mycotoxins in grain corn. A more reliable test called a mould-screen test is very useful in identifying and eliminating what mould species and their mycotoxins that might be present.
If test samples of corn come back positive for mould and mycotoxin such as vomitoxin, one option is to feed the contaminated corn to dairy cows, but adjust the nutrient density of the dairy diet, given the bushel weight of the corn. If the corn samples come back with zearalenone, which is detrimental to dairy cattle reproduction; the best solution is not to feed this mouldy corn at all. Although the dangerous dietary threshold is 250 to 300 ppb for dairy cattle; lower concentrations might be equally avoided, because of its potential toxicity to specific groups of cattle, particularly young and pregnant animals.
Mixing mouldy corn (re: zearalenone) with “clean” feed is not a good idea, because this does not eliminate the problem and reduces the quality and safety of the available good feed. In situations of vomitoxin, commercial mould binders might offer a suitable solution, when there are no other viable dairy feeds are available.
Mould and mycotoxins found in last year’s corn and mixed into a dairy diet might be very harmful to the health and performance of all dairy cattle. It is important to identify if any dangerous moulds and mycotoxins are present and keep them out of feed bunk.