Dried manure solids are one of the most common bedding materials used on dairies today. In the last decade, they have only become more popular. That may be surprising because they cannot beat clean sand for cow comfort or cleanliness but, when managed properly, can be comfortable and clean enough to warrant consideration. Farms choose to use them because they also have several distinct advantages over other bedding types. No management decision comes without trade-offs, and farms using dried manure solids bedding must take steps to minimize their potential disadvantages.
Advantages of using manure solids bedding
Cost
Because the raw materials are readily available, dried manure solids are often appreciably cheaper than other bedding choices. As alternative bedding materials get snapped up for other uses like biofuel or feed, they are even more expensive, which increases the cost gap. That is not to say there are no costs associated with using dried manure solids as bedding. Processing manure slurry requires an upfront investment in equipment and ongoing maintenance of that equipment. Depending on the protocol, varying amounts of fuel and labor will also be necessary. But buying straw, shavings or sand will always be more expensive. With prices rising across the board for other bedding alternatives, this can be an area of cost savings. In addition, dried manure solids does not wear out manure-handling equipment like sand does, extending the life of equipment and reducing repair costs.
Cow comfort
Sand is the gold standard bedding for cow comfort, but beyond that, the amount of material in the bed (regardless of type) has the biggest impact on cow comfort. Using enough dried manure solids to provide adequate cushion is practical because of their lower cost. Good cow comfort pays dividends in multiple areas, from reducing the number and severity of lame cows to increasing lying times. Deep bedding reduces lameness – and subsequently, all the labor, expense and lost production that comes with lame cows. Increased lying times are associated with improved conception rates and milk production. Lameness is a part of welfare evaluations and is a highly visible issue our consumers care about. In addition to the production advantages, improving cow comfort and preventing lameness is important for ensuring cow welfare.
Environmental sustainability
For some farms, utilizing dried manure solids for bedding means they do not have to find an alternative way to dispose of that manure. Soil needs and regulations dictate how much manure can be spread on cropland, so diverting some of this manure to bedding can be an important part of a nutrient management plan.
Challenges of manure solids bedding
The greatest challenge with dried manure solids is the presence of environmental mastitis pathogens in the bedding itself. Cows ideally spend 10 to 14 hours a day lying down. During these times, dried manure solids can expose teat ends to an environment potentially rich with mastitis-causing pathogens for prolonged periods of time.
Research has demonstrated that elevated bacteria counts in bedding are associated with increased cases of intramammary infection. The presence of specific pathogen groups in bedding is correlated with corresponding infections, meaning higher numbers of coliform mastitis cases occur when there are higher coliform counts in the dried manure solids.
Mastitis is an important and expensive disease, so this risk should not be dismissed. In particular, Klebsiella is an issue with dried manure solids when bedding is too wet, and it can have devastating consequences because of the severity of infections and long-term detrimental effects on the cow.
Mitigating the risk of intramammary infections requires a combination of making and keeping the solids as clean and dry as possible and maximizing the cow’s natural defenses.
Bedding preparation
Bacteria require moisture and organic material to grow. Getting dried manure solids as dry and free from live organisms as possible lowers the risk of intramammary infections. There is a huge amount of variation in the characteristics of dried manure solids used as bedding on dairies. Processing strategies may include screw presses to remove moisture, composting in drums or windrows, mechanical drying or some combination thereof.
Bedding bacteria counts
Since bacteria counts in bedding are correlated with mastitis, lowering these counts makes bedding less likely to cause infections. Composting and other heat treatments help reduce bacteria counts.
Benchmark goals for bacteria counts in dried manure solids were established by researchers at the University of Minnesota after looking at bedding samples from a large number of herds from across the country. After correlating intramammary infections with bacteria counts in bedding, they identified cut points that reduced risk of intramammary infections. At least 25% of farms that submitted samples for the trial had to be able to reach these benchmark levels to ensure these are attainable values.
The benchmarks for clean dried manure solids are as follows in cells per cubic centimeter of bedding:
- Coliforms – 500 cells or fewer per cubic centimeter
- Klebsiella spp. – 0 cells per cubic centimeter
- Staphylococcus spp. – 0 cells per cubic centimeter
- Streptococcus and strep-like species – 1,000 cells or fewer per cubic centimeter
Moisture content
Moisture content is also a risk factor for intramammary infections. Processing methods can alter the moisture content of dried manure solids, but the largest factor is climate. In arid climates, the average percent dry matter in unused dried manure solids is 84%, while in more humid parts of the country, dry matter percentages average 36%.
Dry matter percentages above 65% are considered excellent for udder health and are much easier to achieve in certain regions of the country. When dry matter is less than 35%, the dried manure solids bedding poses a much higher risk.
For humid areas like the Midwest and the Northeast, getting bedding dry matter to reach even the moderate category of 35% to 65% can be challenging. Even if bedding can be adequately dried, the increased moisture in the air can quickly undo whatever mechanical process removed the water from the slurry. Farms in humid areas need to carefully consider whether the labor and fuel for drying is worth it when their bedding may remain too moist.
Bed management
All bedding materials quickly become soiled once placed for use. Dried manure solids already have higher bacteria counts than other types of bedding, and with contamination they grow bacteria rapidly.
Well-designed stalls help but can never eliminate all the ways bedding gets wet and dirty. Daily raking or turning of bedding material helps remove the worst of the contamination. It also loosens packed bedding to improve drainage of liquid away from the udder. Adding fresh bedding at least once a week on top of the existing bedding buries the wet and soiled material.
Many farms continue to struggle with stall cleanliness on a once-a-week basis, particularly where humidity is more of an issue. In those cases, adding bedding daily or every other day may be necessary to achieve udder health goals.
Ways to reduce mastitis risk when using dried manure solids
Vaccination
Vaccination for coliform mastitis pathogens is another way to help mitigate risk when using dried manure solids as bedding. There are several USDA-approved, commercially available vaccines for E. coli mastitis as well as one for Klebsiella mastitis. Using such products may help lower cows’ susceptibility to intramammary infections from these environmental pathogens.
Other management practices
Mastitis is a multifactorial disease. Parlor procedures, cow nutrition, teat end health and other environmental factors all play a role in the development of intramammary infections. To maintain milk quality when choosing a bedding that increases the potential for intramammary infections, there can be no other gaps in udder health protocols.
Intentionally putting the udder in contact with manure can seem like a bad idea, and yet many farms achieve and maintain impressive bulk tank somatic cell counts while bedded on dried manure solids. It can be achieved with proper preparation and management of bedding and consistent adherence to other milk quality practices. However, this is easier in some regions of the country. Keeping dried manure solids dry is significantly more difficult in humid environments, and keeping them dry is critical to reducing the amount of bacteria they expose teat ends to.
Dried manure solids can be a great solution in the right climate with the right strategies in place. With limited farm dollars to go around, it can also be an economical alternative while still maintaining excellent animal welfare and environmental sustainability.
