The material a dairy chooses to bed its cows with has many ramifications. Bedding not only has significant impacts on the animal in terms of cow comfort, lameness, and udder hygiene, but it also has economic effects due to price, cost of handling, and milk quality consequences.
Manure is a readily available potential source of bedding on dairy farms, but recycling the solids for such use is often seen as a risk, and it can be in terms of udder health. Using a bedding product that promotes milk quality starts with selecting a low-risk material, keeping it clean, and managing it well. Research has repeatedly shown recycled manure solids to be the riskiest choice, said Sandra Godden, D.V.M., of the University of Minnesota.
However, recycled manure doesn’t always result in lower milk quality. There is significant variation in success among farms that use this material. The professor at the university’s College of Veterinary Medicine cited many herds that do quite well with recycled manure bedding. What are these farms doing differently?
At the National Mastitis Council Annual Meeting, Godden and two farms that have navigated recycling manure solids for bedding discussed how to make the process work for maintaining good udder health and milk quality.
Monitor content closely
Being successful with recycled manure solids requires keeping an eye on two metrics, Godden began: bedding bacteria count and dry matter level.
Bedding bacteria counts can be analyzed in a laboratory, and Godden noted that farmers must be aware of what unit of measurement their lab uses when comparing results to benchmarks. In general, she advised that a sample should have no Staphylococcus or Klebsiella species and low levels of coliforms and Streptococcus species.
As for dry matter content, she said to aim for at least 35% and preferably up to 50%. When bedding is wetter than that minimum level, coliform counts will climb. Providing dry bedding is crucial with all materials, but it is especially important when recycling manure solids where bacteria and pathogens would love to live and replicate.
Ken Buelow, D.V.M., experienced that firsthand on his two dairies in Wisconsin that now milk a combined 7,300 cows. They started using biosolids for bedding on one of the locations shortly after the dairy was built in 2001 with an eye toward sustainability. “Biosolids was one small part of that,” Buelow explained.
While running manure solids through a digester and then a separator before sorting the material outside, it was becoming too wet. “That was one of many problems we faced,” Buelow said of their set up. The solids were spread on top of mattresses three times a week, but by 2007, they decided to move to deep-bedded recycled manure solids.
Gradually, somatic cell count (SCC) went up, there were more mastitis cases (particularly due to Klebsiella), and more animals were leaving the herd. Beulow said that raking the stalls more frequently, using an additive, and their vibrating fluid dryer did not solve the problem. Cows kept having issues, and culling rates quickly climbed.
Get it dry
There are many ways to recycle manure solids, including using a digester, separating, composting, and drying, or utilizing some combination of these processes. Ultimately, the goal is to ensure the solids are separated from the liquid, but it is hard to reach that 35% dry matter target with only some type of press, Godden said. While a press is a necessary step, it does not get you closer to truly clean bedding. That’s why she recommended adding a digestion, composting, or drying step afterward.
Buelow had the digestion and separation parts — so why was the farm still having problems?
With the benefit of hindsight, we can look to more recent research Godden’s team did that compared bacteria counts in green manure solids, material that was digested, material that was digested and drum composted, and material that was digested, composted, and hot-air dried. Unsurprisingly, the green solids had the highest bacteria load. But as each additional step was performed, more pathogens were removed. This had a clinical effect because the same trend was observed for herd intramammary infections. When bedding was more processed and cleaner, there was less disease.
Digestion, Godden explained, results in variable pathogen removal due to factors like overloading the digester, poor mixing, or uneven temperature control. Digestion works best to clean bedding in combination with another secondary step that heats bacteria up; it isn’t so much drying that reduces pathogen load but rather high heat. “Dryers and composters are far more consistent in udder health benefits [than just digestion],” Godden noted.
Buelow eventually determined this logic, and the farm installed a drum dryer to further process its manure solids. This is what they use today for the bedding at both locations, and the veterinarian-slash-dairyman described that they saw steep declines in both SCC and mastitis cases when the new dryer was added. In fact, if the dryer ever malfunctions or is offline for a period of time, they see their old problems return, and the effects can last for two months or more.
With this dryer, they are able to achieve a dry matter content of 55%. All processed bedding is stored inside, and they use it within two days of being processed. This is crucial because the longer dried bedding sits, the more likely bacterial regrowth is.
A new opportunity
Don Niles, D.V.M., of Pagel’s Family Businesses echoed Buelow’s statements about drying and rapid use. “This is not something you stockpile,” Niles said of recycled manure solids. Use them as quickly as you make them, or you will see problems with mastitis.
Niles admitted that their two farms were committed to sand bedding from the beginning. It was a choice he had advocated for with his clients, and they felt strongly about the cow comfort benefits sand provided. When they built their dairies in Wisconsin, sand was the obvious choice.
At the same time, they were also committed to the digester they had installed to take advantage of the opportunity to generate and sell electricity. For years, both sand and the digester worked hand in hand. Sand went through settling lanes and was dried out on the feed pad to be reused. Niles admitted that in their cold climate, the flumes sometimes froze, and it was occasionally a struggle to get enough bedding during those winter months. Largely, though, the system worked. That is, until policy changes eroded the market for the electricity generated by their U-shaped pit digester.
Eventually, the farm found a new use for the digester to be profitable: generating biogas. There was one stipulation from the equipment company that would handle the gas, though. No sand could be in the manure.
“That forced us to switch over to biosolids,” Niles explained.
Their farm now uses a tumble dryer in addition to the digester, but it has the same function as the drum dryer Buelow uses. Getting more moisture out of the manure makes it safer for use from an animal health perspective. Niles noted that their goal for the solids is a lofty 70% dry matter. “If we’re wetter than that, we’ll have mastitis,” he said.
The farm now beds with the solids every day to prevent them from sitting longer and to keep stalls fresh because the cows pack it down more compared to sand, which had been added three times a week. Daily, stalls are raked and lime is added. According to Godden, this is the best way to use lime and other bedding conditioners to lower bedding pH because the effects of such materials only typically last for one day.
For both of these farms, using recycled manure solids successfully required investments of thought, money, and equipment. The systems must be monitored regularly to remain effective. But whether you are looking for a more sustainable bedding solution to close the waste loop on your farm or new revenue opportunities, they prove that you can meet those goals without sacrificing udder health or milk quality.
• Making manure solids work
• Management considerations for new multisite dairies
• Our options for anesthesia
