Pennsylvania Ag Connection - Animal Health Risks from Feeding Flood-Damaged Forages

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Animal Health Risks from Feeding Flood-Damaged Forages
By: Robert Van Saun, Penn State Extension Veterinarian - 10/20/2011

With the significant drought issues in the West, forage availability and cost is at a premium this year. This situation further adds to current high feed cost problems. Yet, another challenge now confronting dairy producers here in Pennsylvania is recent flooding conditions and its impact on forage quality and animal health. The Pennsylvania Department of Agriculture is reviewing the flood damage situation carefully to evaluate potential toxic compounds and sewage contamination of forage to be harvested for feed. Beyond the concerns of toxic contamination, a greater concern for the dairy producer is risk issues related to quality forage production and subsequent animal health. Producing high quality forage is the cornerstone to more profitable production in an environment of high feed costs. What are the concerns to forage production and animal health with flood damaged forage?

The primary concern with flooded forage is increased soil sediment on the plant to be harvested. Amount of soil contamination will depend upon duration and degree of flood water coverage. One issue with increased soil contamination is greater ash or mineral content of the harvested forage. Increased mineral acts as a buffer to acids generated during the ensiling process. Thus the fermentation process will not generate a low enough silage pH to effectively inhibit activity of yeast or mold organisms. The resulting silage will be aerobically unstable; recognized as excessive heating in the silo or secondary heating when removed from the silo. These conditions would also be conducive to mycotoxin production by contaminating mold organisms. Severity of soil contamination can be evaluated by total ash, iron, or acid-insoluble ash determinations from forage analysis testing. Work with your nutritionist or forage testing laboratory to interpret one or more of these values. To compensate for higher buffering activity from soil contamination one would need to increase the fermentation process by applying bacterial inoculants to the harvested forage. You may also need to evaluate plant nonstructural carbohydrate (NSC) content to ensure adequate substrate to drive the fermentation process. Additional sugar or starch sources may be added to the harvested forage when filling the silo.

A greater concern with soil contamination of harvested forage comes from the potential risk for soil-borne bacterial spores adding to the plant's epiphytic bacterial population. Spores from Clostridium and Listeria bacteria are of greatest concern relative to animal health risks. A wide range of Clostridium bacteria are found in nature with some being well-recognized disease pathogens of animals. Many dairy farms routinely vaccinate for seven to eight different Clostridial diseases. Over-eating disease or enterotoxemia (C. perfringens), tetanus (C. tetani), blackleg (C. chouvoei), and botulism (C. botulinum) are examples of disease causing Clostridial bacteria. Talk with your veterinarian about clinical signs for these different disease conditions, though many are seen in animals only as acute death. Clostridium species are common inhabitants of the animal's intestinal tract and are prevalent in manure, thus water contaminated with manure has the potential to increase Clostridia spore exposure in contaminated forage. It is recommended that animals consuming contaminated forage are current relative on their Clostridium vaccine status. There is no practical way to determine clostridium pathogen exposure from silage. Diagnosis is made in the affected animals.

In addition to pathogenic Clostridium species, there are other Clostridium bacteria that can adversely affect silage quality and secondarily animal health. One specific organism, Clostridium tyrobutyricum, is primarily responsible for abnormal silage fermentation resulting in elevated quantities of butyric and isobutyric acids being generated. This organism will consume lactic acid and protein in silage to produce butyric acids and ammonia resulting in low lactic acid concentrations and higher silage pH. Growth of this organism is favored by high moisture (>70%) silages. Cows consuming butyric acid silage are at risk for ketosis as the butyric acid is converted to beta-hydroxybutyrate, one of the ketone bodies, in the rumen. Thus transition cows should not consume butyric contaminated silage in an effort to minimize metabolic disease risks in early lactation.

Butyric silage can be readily recognized by its rancid butter/milk smell and green slime color. However, butyric acid content of silage can range from <0.01 to >8% of dry matter. Values of 2% and higher are high risk forage and should not be fed to transition cows. Suspect silage can be recognized by its low dry matter content (<30%) and high soluble protein (>60%). Ammonia as a percent of crude protein will also be elevated (>20%) in these forages. Butyric acid can be quantified directly in forage samples by completing a fermentation profile analysis with most forage laboratories. Prevention of clostridial fermentation starts with proper moisture when harvesting. Use of bacterial inoculants may also be of value in promoting a more homogeneous fermentation pattern. Butyric silages are aerobically stable, therefore recommendations suggest removing silage prior to feeding and "aerating" to allow volatilization loss of butyric acid. Alternatively, blend silage sources to reduce total intake of butyric acid (<75 gm butyrate/day) and minimize the feeding to transition cows.

Another risk often associated with clostridial fermentation comes from another spore-forming bacteria currently in the news, Listeria monocytogenes. Like Clostridia, Listeria is a soil-borne spore-forming bacterium that is ubiquitous in the environment. Listeria is a significant zoonotic disease that typically causes circling disease in cattle, but can induce abortions and meningitis in both cattle and humans. The spore can develop into the infective vegetative state only under the right environmental conditions. Listeria prefers high pH (>5.0) and low oxygen environments. With good fermentation, corn silage pH should not approach 5.0, though alfalfa or clover silage can easily approach this value. However, if a clostridial fermentation has taken place, then silage pH may be elevated enough to allow Listeria spores to develop. Typically, Listeria is a sporadic disease entity, but outbreaks within a herd can occur. Poorly packed areas of the silo (along walls or in corners) are high risk areas for Listeria growth. Prevention is focused on ensuring a good fermentation with stable and low pH in the final silage product. Inoculant usage as well as silo filling practices are critical management issues to address.

Flood damaged forages add yet another challenge to the dairy industry this year as fall harvest gets into full swing. Soil and soil-borne bacterial spores can pose significant health risks to animals consuming flood damaged forage. The key to preventing any health problems is to ensure proper forage harvesting practices are implemented, especially emphasizing correct moisture level and chop length to ensure proper packing ability. Bacterial inoculants to promote a good fermentation generating low pH with high lactate content should be strongly considered.

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