As the calving season is fast approaching, it is appropriate to address one of the important causes of abortion in cattle that being mouldy feed. Mould can be a result of either fungal or yeast infection of cereals or forages grown for feed. Infection occurs in the field during plant growth or during harvest/storage. Examples of infections that occur during plant growth include fusarium head blight and ergot while those arising during hay or grain storage include mouldy sweet clover and growth of a number of fungal species that produce mycotoxins.
Fungal infections of plants usually occur when there is a cool, wet growing season. This is the case with ergot in cereal grains such as rye or barley. The plant’s flowering period is extended under these conditions which promotes infection by the fungal species Claviceps purpurea. Storage infections occur when hay is put up at too high a level of moisture (greater than 15 per cent) or there is the right combination of moisture and temperature during grain storage, particularly corn.
With respect to health and productivity of cattle, mould contamination of hay or grain supplies can result in several issues. First, moulds are living organisms and their rapid growth will reduce the energy value of the feed, particularly forages. Protein quality and content can also be adversely affected. Common energy discounts applied to mouldy hay range from five to 10 per cent.
Mouldy/dusty hay also has a negative influence on feed intake as it is simply not as palatable as fresh hay. Both of these issues influence the adequacy of the diet and if unaccounted for there is the potential for undernourished cows that lose weight over the winter. A third issue related to excessive mould contamination is its potential to cause abortions in cattle and respiratory disease in cattle and humans. Abortion due to a fungal infection is known as a mycotic abortion and is a result of feeding mould-contaminated hay to pregnant cows. The fungal infection spreads from the intestinal tract to the placenta where it localizes and causes thickening of the placenta (placentitis). Abortions tend to occur between six and eight months of gestation (Source: Manitoba Food and Rural Development).
Feeding mouldy sweet clover can also result in abortions and neonatal mortality, although the mechanism is different than with mycotic abortions. In this case, mould present on the sweet clover can generate dicoumoral, which is an anti-clotting substance. Abortions and calf death loss from excessive bleeding can occur at or shortly after calving. Moulds can also cause allergic reactions in both cattle and people who breathe dust from mouldy hay. In people, mould dust can contribute to development of Farmer’s Lung while cattle can develop pneumonia or other respiratory issues.
As serious as these issues are, moulds hold one more nasty surprise for those who ignore their presence in feeds. Mycotoxins are byproducts of fungal growth that can cause poisoning in animals. Mycotoxins can accumulate as the plant grows or during storage. 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 (vomitoxin) in wheat and barley and alfatoxin in corn. Symptoms of mycotoxin poisoning include decreased feed intake and growth, abortions, reduced milk production and increased morbidity and mortality.
Knowing that mouldy feed has the potential to cause serious disease and production issues, it would seem that the simple answer is to avoid feeding mould-contaminated feed. This, however, is not as easy as it seems. First, all feeds are contaminated to some extent with mould. Feed-testing laboratories for example conduct mould counts on feed samples with scores ranging from relative low values of less than 10,000 colony forming units (CFU) per gram of feed to heavily contaminated samples at 10 million CFU per gram of feed. While indicative of relative level of infestation, there is no clear mould count guideline that indicates safety, particularly for pregnant animals. Secondly, not all moulds produce mycotoxins and those that do require unique growing conditions to infect the plant as is the case with the fungus that causes ergot or unique temperature and moisture conditions to produce storage mycotoxins.
This gets us back to the question implied in the title of this article — “What do you do with mouldy hay or grain?” As should be evident from the above discussion, the health and productivity of all animals are at risk from mouldy feed. However, pregnant cows are particularly susceptible, with abortion one of the most serious consequences. My recommendation is to avoid feeding mouldy hay or heated grain to pregnant cows or heifers. The risk is too great! If you do have to feed hay that is heavily contaminated with mould, blending with good-quality hay can help reduce contamination. Your best option is to blend the mouldy feed into rations for feeder cattle. While these animals are less susceptible to mould and their mycotoxins, there is still a need to keep a close eye on their health and performance. In the case of suspected ergot or other mycotoxin contamination, have the feed tested at a qualified laboratory. If in doubt, seek the advice of a qualified nutritionist!
This article was originally published in the February 2016 issue of Canadian Cattlemen