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Rutgers – Ask the Expert – Round Bales

Question: I would like to start feeding my horses a round bale in their fields in the winter; however, I have been told this is a bad idea. Why would feeding round bales be bad for horses?

Answer: Large round bales of hay, usually weighing 800 to 2000 lbs, are easy to use if you have the proper equipment to move them around, and fairly economical compared to square bales. However, a study from the University of Minnesota discovered that if they are placed directly on the ground, uncovered, the cost benefits are less because so much hay is wasted from trampling by horses. There are several round bale feeders on the market that are quite effective at reducing wastage. If bales are left on the ground, mold can form at the bottom of the bales. Although the mold is probably not pathogenic, once the mold spores have formed they will persist, even in freezing weather, and can cause allergic reactions in some horses. Most horses will avoid eating moldy hay if they can. Round bales are certainly used extensively, especially in the more arid western states, so feeding round bales is not necessarily a bad idea. However, in the humid, warm regions of the country, one needs to take some precautions.

Botulism is the main concern when feeding round bales in a humid climate. It is caused by a toxin secreted by a Clostridial bacterium under certain anaerobic, humid conditions. The bacterium is fairly ubiquitous in the soil in many regions and even in the intestinal tracts of animals. The bacterium itself is not pathogenic. However, in anaerobic environments such as that seen in a dead animal’s carcass or in moldy or fermenting hay, the bacterium sporulates and releases a toxin (Botulin). During the baling of hay (even the small square bales) small animals like mice, moles, rabbits, snakes and even baby deer can get hit by the harvesters and have their carcasses incorporated into the hay bales. As they decompose inside the tightly baled hay where there is little to no oxygen present, the decaying tissues provide the necessary conditions under which the Clostridial bacteria release toxins into the surrounding hay. Even if the carcasses are found and removed, the hay will remain contaminated and could potentially harm the horses eating it. If you do find a carcass in a bale of hay, discard all of the flakes in contact with the carcass or even better, the whole bale. It is more likely for toxicity to happen with large round bales than with small squares because it is easier to detect a dead animal when feeding the smaller “flakes” or “laps” of hay from the square bales. Horses can recover from botulism, and the severity of the disease will depend on the amount of toxin ingested. Again, most horses would avoid eating hay that “smells” like a dead animal, even if the carcass is no longer present. Nevertheless, it is strongly recommended that horses fed round bales, especially in humid climates where it seems to be more of a problem, are vaccinated against the botulin toxin. Unfortunately there are several different strains of these bacteria, and the vaccine only protects against the two most common toxins. The vaccine does not guarantee 100% protection, but it is certainly worth the cost.

Dr. Carey Williams is the Extension Specialist in Equine Management for Rutgers Cooperative Research and Extension. Her research focus is in equine nutrition and exercise physiology. She coordinates “Ask the Expert,” a feature of the Equine Science Center website.

Medical Disclaimer
This material is for educational purposes only and is not intended to diagnose, prevent, or treat any illness. Any recommendations are not intended to replace the advice of your veterinarian. Any products mentioned are not intended to diagnose, treat, cure, or prevent disease. Mention or display of a trademark, proprietary product, or firm in text or figures does not constitute an endorsement by the Equine Science Center or Rutgers University and does not imply approval to the exclusion of other products or firms.

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