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Dealing With Moldy Hay

published: January 22nd 2010
by: Dr. Cathy Bandyk
source: Bovine Veterinarian

The conditions during harvest of this year’s corn crop brought a sharp reminder of the potential issues – and even hazards – surrounding moldy feed grain. Strategies for dealing with reduced feed value and mycotoxins are hot topics right now for producers and nutritionists. But grain farmers haven’t been the only ones impacted by challenging weather; there are plenty of producers who need answers to the specific question: What about moldy hay?

Strictly speaking, every bale of hay has some mold. But when there is enough to see, is that something to worry about? There isn’t a simple answer to that question, but – depending on the type (species) of mold, amount of fungal mass (both the stringy white mycelium and the dusty spores), and class of animals being fed – there are several areas of potential concern.

Palatability.

Significantly reduced intakes have been observed in cattle fed moldy forages. This response may be driven by taste, dust, lowered nutritional quality, or a combination of these factors. The bottom line is a reduction in nutrient supply for the animal, and often increased waste of the hay.

Reduced Nutrient Content.

As mold develops on a feedstuff, these fungi utilize nutrients from the feed itself to support their growth. That represents a net loss in energy content; the rumen microbes aren’t going to be able to feed on something that has already been used up! An additional concern is potential reduction of protein quality and digestibility. Extensive mold growth is often accompanied by heat damage, which can bind some of the protein in the hay into compounds cattle cannot digest or make use of. These effects can be significant: in work done at SDSU, when water was added to hay to create mold, nutrient value was decreased 15-20%.

Physical Response to Mold Spores.

The “dust” in moldy hay is actually a collection of the seed-like reproductive stage, or spores, of the mold. When these are breathed in, irritation and infection may result. While this is typically a bigger issue for horses (and people), it is possible for spore inhalation to trigger respiratory problems in cattle. In animals experiencing respiratory allergy or “bovine interstitial pneumonia,” oxygen is prevented from getting into the bloodstream. An infected cow will gasp for breath, and if she is pregnant, the developing fetus may die due to a lack of oxygen. Abortion usually follows in a couple of days.

Toxic Compounds.

While produced by only a handful of the thousands of fungal species that can be found in hay, mycotoxins can wreak serious damage in a herd when present. They present a management nightmare: visible mold may (but usually doesn’t) indicate the presence of these dangerous substances; the amount produced is difficult to predict; if present, they will not be distributed evenly in the feed; symptoms may not appear for days or even weeks; and in cattle the response is often chronic rather than acute, resulting in performance losses that may never be identified. All of the following have been attributed to mycotoxins produced by molds growing on hay:

-- Reduced intake/feed refusal                  -- Liver damage

-- Impa ired nutrient absorption                -- Diarrhea, bloody scours

-- Suppressed immunity                            -- Ketosis

-- Cellular death and organ damage          -- Altered rumen function

-- Altered endocrine systems                    -- Impaired fertility

-- Photosensitivity                                    -- Reduced performance

-- Death

Affiliated Pathogens

Conditins that lead to mold growth are also favorable to the development of certain harmful bacteria. A key example would be Listeria monocytogenes, the infectious agent in Listeriosis.

Special Concerns with Sweet Clover.

Sweet clover hays contain a compound called coumarol. In the presence of mold, it is converted to dicoumarol, a powerful anti-clotting agent. Cattle consuming moldy clover hays may experience hemorrhages, respiratory stress, abortion, and even death.

With all that said, most cattlemen will periodically find themselves with an inventory of moldy hay that needs to be utilized in their feeding program. In these situations, keep the following points in mind:

- Feed a balanced diet, with adequate degradable protein and soluble energy, to support optimal rumen function. Ruminal microbes are able to degrade many mycotoxins, rendering them harmless, and good nutrition will support this activity.

- Be sure the diet is adequate in selenium and vitamin E, both of which play key roles in the animals’ defense against oxidative stress. In some cases, feeding synthetic antioxidants may be justified.

- Dilute the moldy feed with higher quality feed.

- Selectively feed moldy hay to non-pregnant, healthy animals that are under relatively low stress conditions.

- Avoid feeding extremely dusty (spore-ridden) hay where ventilation is poor.

- Consider using liquid supplements to help control dust (and enhance rumen activity).

- Evaluate available commercial products that have demonstrated ability to bind to mycotoxins. These are typically select yeast fractions or extracts that adsorb to specific toxins, and carry them out of the animal undigested and unabsorbed.

As a final point, it is worth noting that many moldy hays may be fed with no apparent detrimental effects. In a pair of experiments done at the University of Manitoba, increased presence of mold caused a 40% drop in feed intake by young Holstein heifers, but then failed to elicit any changes in intake, stress measures or short term health in a group of Angus calves. Management of moldy hay needs to be planned in the context of risk management, and monitored through the feeding season.