MFA TECHNICAL BRIEF
Challenging hay conditions will affect feeding efficacy and safety
We had some interesting hay-making conditions this year. There was plenty of hay down during summer pop-up thunderstorms or more prolonged rain events, and, as always, there was plenty of humidity regardless if it rained or not. Fall cuttings weren't much different. Such conditions are the beginning of many undesirable things: reduced subsequent forage growth, loss of nutrients, mold growth, increased harvesting loss, increased harvesting costs, hay being put up at a higher moisture, heat damaged protein, brown spots, barn fires, etc.
Given high humidity, expected forage drying in storage may not occur and the hay may have high enough moisture to permit mold growth. On untreated hay (hay that is untreated with mold killers such as propionic acid, ammonia, sorbic acid/salts, etc.) mold will grow at moisture levels above 14 percent to 15 percent. The PhD forage geeks will wring their hands and remind us that the measurement should really be water activity rather than moisture. But measuring "water activity" is a tedious and hard-to-arrive-at-in-the-real-world formula. Moisture is easier to measure and is close enough to let you make management decisions.
Mold growth produces heat and can result in large amounts of organic matter loss. Under some conditions mineral can be lost-leaching out potassium is common.
In some situations heating can be great enough to cause auto-oxidation, "charring" or spontaneous combustion leading to full-fledged hay fires. By rights, hay burns somewhere around 350F. But if you see what looks like steam, which is water vapor coming off the center of bales, you need to take immediate action. If you have a thermocouple or thermometer that pegs a temperature of no greater than 130F, the temperature will drop. If it hits 150F, the hay temperature may go down, which is good, or it may go up, which will be troublesome. If the temperature is greater than 175F, take immediate action. Here, immediate action means call the fire department. Then you call me and ask about carrying cows through winter on a low hay inventory.
Drying of stored hay is increased by:
1. Ventilation: Having air space between bales increases air movement.
2. Adequate head space: Providing enough gap between the top of the stack and the roof allows moisture to move up and out the top of the stack.
3. Avoiding other wet products in the same area: In areas of low air circulation, additional wet material raises the humidity of the storage area.
4. Having smaller stacks.
5. Using alternating direction of stacked bales.
6. Avoiding use of tarps: Tarps on the top of a hay stack trap moisture via condensation and supports the growth of mold.
Molds commonly found in hay include Alternaria, Aspergillus, Cladosporum, Fusarium, Mucor, Penicillium, and Rhizopus. In hay, mold growth-structures are comprised of two components: mycelium and spores. Mycelium is the stringy growth structure of fungi. It looks sort of like the strands of a cotton ball. Spores are the reproductive, seed-like structure. A principal concern for cattle is the total amount of mycelium and spores combined or the total "fungal biomass." In hay, the white mold in the bale is the mycelium and dustiness is from the tiny spores. These mold-produced spores are the "dust." They can cause respiratory problems, especially in horses or other animals fed in poorly ventilated areas. The physical dust problem associated with moldy forage can be reduced by ensiling, mixing with a high moisture feed or wetting the hay.
Most molds are harmless; they don't produce known mycotoxins. But the fungi did use some forage energy-it is lost for livestock purposes. Under some conditions, Aspergillus, Fusarium and Penicillium will produce mycotoxins. Many of the commonly diagnosed mycotoxins are produced in the field prior to harvest. Here in the humid Midwest, we are well-acquainted with infected fescue. In harvested or stockpiled infected fescue, the toxic alkaloid concentration will decline over time. There is substantial discussion about mycotoxins in forages because several species and or mycotoxins may be present. Try as we might, control methods are not consistent nor are the diagnostic methods. Same goes for treatment recommendations. More research is needed.
Feeding moldy hay to livestock is a frustration. The effect of mold on livestock health can vary depending on the type of livestock and fungi. Horses seem to be most sensitive to mold. Mold spores exacerbate respiratory conditions such as heaves and digestive problems like colic. Cattle can generally tolerate and eat a mold on hay without problems. Canadian work on molded hay showed limited reductions in digestibility and intake of molded hay, even up to as high as 10 percent fungal biomass in the hay. Hay harvested and stored under ideal conditions often contains 1 to 2 percent total fungal biomass while severely molded hay may contain up to 10 to 12 percent total fungal biomass.
The researchers concluded, "Presence of fungal biomass in alfalfa hay does not affect the rate and extent of DM, CP, and NDF degradation of feedstuffs commonly used in ruminant rations but may affect rate and extent of DM degradation of highly lignified feedstuffs such as barley straw." To avoid livestock problems, the conservative approach is to minimize feeding hay to more sensitive livestock.
The interpretation of spore counts which have been suggested are:
< 500,000 per gram: low risk
500,000 to 1 million: relatively safe
1 million to 3 million: feed with
3-5 million, dilute: feed with caution
> 5 million: do not feed
(Richard et al 1993)
Dr. Jim White is ruminant nutritionist for MFA Incorporated.