Avoiding Botulism in Spring Round Baled Silage

Making silage in round bales (baleage) allows timely harvest of spring forage resulting in a high quality stored forage due to timely cutting and less rain damage. Small grains are one of the most popular forages ensiled as baleage. These forages produce high tonnage and palatable stored feed when harvested early. However, the frequency of clostridial fermentation and even botulism with small grains is greater than almost any other forage.Picture1

Clostridial fermentation can be avoided with attention to a few key details. First, there are several species of Clostridium bacteria but only C. botulinum causes botulism. Clostridium numbers in forage are normally low, but are introduced into small grain baleage mainly from dirt raked into the windrow or splashed onto the forage by heavy rain events.

Good fermentation in wrapped, high moisture small grain forage depends on the following: 1) Cutting early so there are adequate quantities of fermentable carbohydrates, 2) adequate numbers of lactic acid bacteria present on forage surfaces, 3) keeping dirt contamination to a minimum, 4) baling at moisture contents less than 65 to 70%, 5) wrapping with at least six layers of plastic within 12 to 24 hours, 6) maintaining plastic integrity until feeding and 7) testing forage to know fermentation characteristics.

Cutting early

Small grains should be harvested at the boot to early head stage for the best compromise between yield and quality. Forage at this stage will have adequate water soluble carbohydrates for good fermentation. Be very diligent to cut early with cereal rye as it rapidly declines in quality and palatability after heading.

Adequate numbers of lactic acid bacteria

Good baleage requires an anaerobic environment that fosters the growth of lactic acid bacteria (LAB) so bale pH drops quickly to 5.0 or below and high levels of lactic acid are produced (>3% of dry matter). These characteristics will inhibit the secondary clostridial fermentation and possible botulism formation. Populations of lactic acid bacteria (LAB) can sometimes be low on spring forage due to cool temperatures. Commercial silage inoculants can be applied to ensure that adequate LAB populations are present. Inoculants are best applied in liquid form at baler. Small grain forage will ferment without inoculants, but inoculant treatment will typically result in lower pH and higher lactic acid.

 Watch out for dirt

Dirt is the main way that Clostridium bacteria are introduced into baleage. Adjust rakes so that they have the minimum down pressure required to move the forage into a windrow. A forage test for ash content can determine if high levels of dirt are present. Ash values greater than 11% indicate dirt contamination and higher risk for clostridial fermentation.

 Baling at moisture contents less than 65 to 70%

Getting the moisture right is one of the best ways to inhibit or prevent clostridial fermentation. Estimating moisture content (MC) in the forage before baling is possible, but no method is both fast and accurate. Windrow moisture can be estimated by feel (the dishrag or twist test) or drying by forced air or microwave or by electronic moisture testers. Commercially available testers are an option for estimating forage moisture levels, and will test either in the windrow or the bale. Windrow testers have always been less accurate because of the difficulty of getting loose forage compressed uniformly enough for good probe accuracy. Bale probes have recently become designed so they can estimate moisture above 40% and are more accurate than windrow testers. Obtain at least three moisture readings to create an average value. Either type costs approximately $300.

It is essential that the forage wilts from its fresh MC (80%) to less than 65 to 70%. In most years, this means cutting one day with the widest possible swath (for maximum solar radiation interception) and raking and baling the next day after the dew is off. In 2019, some experienced producers that cut early had to wait multiple days because of wet soil and poor drying conditions. It is better for baleage to be too dry than too wet. More information on estimating moisture is available in AGR-235, Baleage: Frequently asked questions.

 Use enough plastic

Six layers of plastic provides the necessary oxygen exclusion for fermentation and gives protection from punctures and tears. For an individual bale wrapper, ensure that two layers of wrap are applied during each full rotation of the bale and there is 50 percent overlapping of successive layers. For an in-line bale wrapper, overlapping layers should be spaced no more than 5 in. apart if using a 30 in. roll (30 in./6 layers = 5 in. between edges of layers). When non-uniform bales are wrapped with an in-line wrapper, it may be helpful to apply extra plastic at the joints. The change in bale size makes it difficult for the plastic to seal, allowing oxygen infiltration and mold growth. Do not apply too little plastic or oxygen will penetrate the bale and cause spoilage, mold growth, and feed losses.

Maintain plastic integrity

Keep holes and tears in plastic mended, especially in the first month when most of the pH drop and lactic acid production occurs. In a recent botulism case, a large hole in plastic was the likely cause for botulism toxin formation. This lot of baleage also had very high ash (dirt) content and high moisture.

 Final thoughts

Preventing clostridial fermentation and botulism is very possible with small grains. Cut early, wilt to 65% MC or less, wrap quickly after baling, and use six layers of plastic to achieve good fermentation. All steps are important, but going to the extra trouble of assuring yourself that moisture has dropped from 80 to 65% or below is the key to preventing clostridial fermentation and botulism potential. A good forage test that reveals ash content as well as fermentation characteristics will tell if your baleage is at risk for feeding problems. Contact your local County Extension Agent for how to collect a sample for your baleage.