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Watch Out For Mouldy Hay


Picture this: it’s the middle of winter and a couple of months from calving. You go to where your haystacks are stored and go through the morning feeding routine. As bales are rolled out, much of the hay is white and dusty, sure signs of mould. You pick out one or two more bales and they’re mouldy too. Your first thoughts might be, “What are risks of feeding mouldy hay to pregnant beef cows?

This scene will play out on several cow-calf operations across the Prairies after a wet summer made putting up good mould-free hay, difficult. Not only did scattered showers and high humidity force longer drying periods, but when this hay was finally baled it was most likely not dried below 14 to 15 per cent moisture to prevent mould growth in storage. Opening a bale and finding it mouldy doesn’t always mean it contains dangerous mycotoxins (poisons produced by mould), but the significant presence of mould can still negatively affect beef cow health and performance.

The white mould covering stems and leaves of hay is the stringy growth of the fungi and its dusts, which are actually reproductive spores. Together, they make up the total fungal biomass of the mould organism.

Some field trials with hay moulds show cattle will eat most hay with about one to two per cent storage mould without much problem. Put hay with over 10 per cent contamination in front of them, and cattle will likely reject it or at best slow consumption. Subsequently, it makes sense that beef cows that don’t eat their daily forage allotment are probably not receiving all essential nutrients to get them through a cold winter.

Aside from a cow herd’s predictable poor consumption, most mouldy hay is not the most nutritious feed in the first place. Mould is a living organism and literally competes with the cattle for the same essential nutrients such as carbohydrates (energy source) and available protein found in otherwise good-quality forage. For instance, it is conservatively estimated that established mould reduces the energy content of hay and other types of forage (i. e.: silage) up to 15 to 20 per cent. As a result, producers might provide extra energy and protein supplements, so overwintering cows will consume this forage and meet increasing nutrient requirements as they get closer to calving.

This loss of good feed intake and nutritious feed are only two problems when feeding mouldy forage. Granted, cattle and other ruminants might have a higher tolerance to the adverse effects of mouldy feed compared to other livestock such as pigs and chickens, but an exact safety level in cattle is not established. Many researchers have demonstrated beef cattle can breakdown most feed mould organisms and detoxify a percentage of their mycotoxins, but there are several factors that determines any such measurable and definite capacity.

It must be first known how the mouldy forage is to be fed and how badly this forage is contaminated. After mouldy hay is eaten by cows, we must assess the digestibility of the forages by the ruminal microbes as well as negative impact of mould upon natural fermentation. This estimation is then followed by calculating the speed or rate of forage passage through the rest of the digestive tract of the cow.

There are animal factors that determine how well individuals in a cow herd are able to detoxify mouldy forage as well. Healthy cows in good body condition, who easily tolerate cold winters, have a natural higher ability to detoxify molds compared to cows either fighting a disease, reared on a poor feeding program, or just trying to stay warm. Consequently, it’s a general consensus that mouldy hay and other forages should not be fed to beef cows undergoing any considerable stress.

Despite the cows’ ability to detoxify forage mould, it doesn’t mean they can’t be adversely affected in other ways. They can be infected with mycosis, which are associated diseases caused by feed moulds that easily invade various body locations such as the lungs, udder, uterus or intestines. Several respiratory infections in cattle have been traced to mould spores from mouldy feed. Likewise, coughing, shortness of breath and chest pains are common symptoms of “farmer’s lung” and a dire warning to producers working with mouldy hay.

Luckily, most people are apprehensive when feeding visibly mouldy hay to their cow herd. They should also realize not all hay mould contamination is always visible or consistent throughout individual bales or among several bales in a load. If mould is obvious or suspected, a mould-count test is often recommended, which literarily counts the number of actual mould spores in forage samples.

Mould count tests are rather inexpensive, but their usefulness as sound information is also limited. The results tell producers there is mould present and the magnitude of infestation, yet it fails to reveal the presence of mycotoxins, regardless of mould count. If one suspects problematic mouldy forage for pregnant beef cows, it is a good idea to conduct a more extensive mould-screen test in order to identify mould species and mycotoxins. Since, specific mycotoxins found in mouldy feed have been known to cause spontaneous abortion, reduced future reproductive performance, and infertility in beef cows, some producers don’t take the chance and test their forages, accordingly.

To be absolutely safe when dealing with mouldy hay, the golden rule has been to avoid feeding it to pregnant beef cows!

However, if producers are forced to feed mouldy hay, these steps can minimize its impact upon cows: (1) collect samples and conduct a mould count and mould-screen tests, (2) avoid feeding mouldy hay to stressed animals, (3) dilute it with clean forage and feed to less than 25 per cent of the diet, (4) gradually introduce diet with mouldy forage and (5) supplement energy, protein and extra minerals and vitamins. Keep in mind these steps are not a long-term solution, because although a single concentrated dose of mycotoxins from mouldy hay can poison beef cows, it’s likely that low-level consumption can cause unseen chronic troubles.

PeterVittiisanindependentlivestocknutritionist andconsultantbasedinWinnipeg.Toreachhim call204-254-7497orbyemailat [email protected]

About the author


Peter Vitti is an independent livestock nutritionist and consultant based in Winnipeg. To reach him call 204-254-7497 or by email at [email protected]



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