Are you harvesting more than you think?

There is an exhaustive list of agronomic, storage, nutritional and anti-nutritional factors associated with forage quality that could be considered the most important metrics. From crop yield to disease and insect resistance, to density and shrink, to ash and lignin, and further on to neutral detergent fiber (NDF) digestibility, starch availability, total tract starch digestibility (TTSD), chop length, particle size, etc., and the list goes on. But does “forage microbial hygiene” make the list? If so, where does it rank among all the other considerations?

Keith A. Bryan

Technical Services Manager – Ruminant DFM and Silage Inoculants / Chr. Hansen Animal Health & Nutrition

Email Keith A. Bryan

Eric Dorr

Epiphytic micro-organisms

On plants growing in the field just prior to harvest, the naturally occurring population of microbes (epiphytic micro-organisms) can exceed 10 million colony-forming units (CFU) per gram of forage – and not all are beneficial organisms (Table 1).

Typical populations of epiphytic micro-organisms on plants prior to ensilling

Generally, lactic acid bacteria (green) are considered desirable for fermentation, whereas acetic and propionic bacteria occur in so few numbers they are thought to be of little significance (yellow). The micro-organisms listed in red, however, tend to be undesirable for fermentation, storage and feedout.

Furthermore, both disease-causing (pathogenic) and non-disease-causing bacteria and fungi (yeasts and molds) can be brought in with the harvested crop or can flourish during storage or at feedout. These organisms, along with their waste products or metabolites, have the potential to be anti-nutritional factors that can negatively impact health and productivity of your high-producing dairy cows.

Bacteria: Beyond listeria

Regardless of the source or timing of their proliferation, spoilage micro-organisms can rob your cows of highly digestible nutrients or, more importantly, cause digestive upsets, chronic disease or even death.

The classic bacterial contaminant of silage has been Listeria monocytogenes leading to listeriosis; however, as we learned more about listeria and how to manage or even control it, it fell from our radars. Now, we are more likely to contend with clostridia and enterobacteria, as well as yeasts and molds from the standpoint of “forage microbial hygiene.”

Clostridia

Clostridia contamination of forage, primarily wet alfalfa haylage leads to extensive dry matter loss, elevated butyric acid levels and potential negative impacts especially for fresh and transition cows. While clostridia species that produce butyric acid in silage (e.g., butyricum, tyrobutyricum, sporogenes, etc.) can be reduced and effectively controlled with a reputable, science-based, research-proven bacterial silage inoculant and improved management practices, Clostridium perfringens may also be present and can have significant anti-nutritional effects on high-producing dairy cows.

Clostridium perfringens type A has been implicated in hemorrhagic bowel syndrome (HBS), as well as other digestive disturbances. The loss of cows is obvious, but what about the chronic subclinical losses that potentially occur daily without noticeable effect? Are you harvesting and providing your cows with “clean forage?”

Enterobacteria

Enterobacteria, such as salmonella, E. coli, klebsiella and shigella, are organisms typically found in the intestines of humans and animals. These organisms are undesirable in silage because they compete with beneficial bacteria for nutrients prior to and during ensiling. Their growth is known to increase the buffering capacity of the crop once ensiled, which raises the pH and lowers aerobic stability. Conversely, enterobacteria are essential for the degradation of nitrate (NO3) to other nitrogenous compounds that can inhibit the growth of clostridia and reduce the production of butyric acid.

Although most of the enterobacteria are regarded as non-disease-causing, some do contain a toxin that has been associated with feeding problems on dairy farms. Also, if soil or manure ever contaminates your silage, there is an increased chance your feed will contain one or more enterobacteria species.

Fungi: Yeasts and molds

We all know the scenario where conditions were less-than-ideal at harvest. You were rushed to get the crop in and didn’t pack it as well as you wanted, and it is heating upon exposure to air at feedout. Heating is primarily a result of “wild-type” yeast growth as they consume lactic acid and other nutrients meant for your cows to make milk. This consumption of lactic acid increases silage pH, which makes it easier for molds such as aspergillus, fusarium and penicillium to grow and further reduce silage quality.

Not only are you losing silage dry matter, but the yeasts and molds pose other potential hazards, such as interfering with the natural microflora of the rumen and presenting mycotoxin contamination. Yeasts are capable of significantly altering normal digestive and metabolic processes in the rumen, especially by decreasing NDF-D (fiber digestibility), and they are suspected of contributing to milkfat depression.

Just because there are molds doesn’t mean there are mycotoxins, and just because there are no visible molds doesn’t mean there aren’t mycotoxins. It is important to note, however, that aspergillus, fusarium and penicillium molds are thought to be the most problematic with regard to mycotoxin production. Molds originating on the crop in the field or resulting from poor ensiling practices are undesirable for two primary reasons:

They result in spoilage that alters nutrient composition, feeding values and feed inventory.
They produce a variety of mycotoxins that can cause moderate to severe disease-like conditions in lactating dairy cows due to low-level consumption over extended periods of time.

Today’s high-producing dairy cows have a faster turnover of rumen contents due to higher dry matter intake than the lower-producing cows of the past. Because of this, they have less ability to detoxify feedstuffs because feed spends less time in the rumen where the natural detoxification process occurs.

The effect of mycotoxins generally is characterized by reduced dry matter intake or feed refusal, decreased nutrient absorption and impaired metabolism, suppressed immune function and altered microbial growth. Since many of these symptoms can also result from other types of diseases, or environmental challenges, the presence and effect of mycotoxins can easily go unnoticed.

Potential solutions

We know numerous field-borne and storage, anti-nutritional or pathogenic micro-organisms are inhibited when pH in the silage pile or bunker drops below 4.5. This is usually achieved by applying a science-based, research-proven silage inoculant with exhaustive research demonstrating effective pH decline.

Just as important is maintaining a healthy environment within the digestive tract of high-producing dairy cows. This is most effectively accomplished by feeding science-based, researched-proven probiotics that provide essential microbial support to the natural digestive, immunological and barrier function properties of the rumen and intestinal epithelium.

Conclusion

Bacteria, along with mold and yeast, have the potential to contribute significant anti-nutritional components to forages. These naturally occurring micro-organisms may come in with the harvested crop or they may become established and grow during storage and feedout. Although shrink or digestible nutrient loss is a potential outcome of undesirable spoilage micro-organisms, they are also likely to have a negative effect on the digestive system and the overall health of your high-producing dairy cows.

Are you harvesting more than you think? Is “forage microbial hygiene” on your list of key metrics for quality forage? If not, you may want to consider the positive impact of having “clean feed” for your dairy nutrition program and put a system in place to make needed improvements.