Recycled manure solids offer dairy producers an attractive combination of availability, cost savings and manure-management benefits. But there is an obvious trade-off: the material starts as manure, meaning it arrives with bacteria and provides an organic environment where bacteria can grow.
“This is in fact recycled manure. And so not only is it an organic bedding material that will support bacterial growth, but it already comes pre-seeded with bacteria,” says Dr. Sandra Godden, professor at the University of Minnesota College of Veterinary Medicine.
That inherent risk has made recycled manure solids (RMS) a concern for udder health. Yet Godden suggests the question isn’t simply whether RMS is a good or bad bedding material. How the material is processed and managed can change the bacterial load that ultimately reaches the cow.
This was the subject of conversation when I sat down with Dr. Godden at the American Association of Bovine Practitioners Annual Conference last week. To hear more from her, along with other veterinary experts, on the newest technique and technology advancements in bovine health, tune into the latest episode of The Bovine Vet Podcast.
Recycled manure solids bedding: Potential benefits and drawbacks
Recycled Manure Bedding and Mastitis Risk
Cows spend 12 to 14 hours per day lying down, making bedding an important source of teat-end exposure to environmental mastitis pathogens. Research has consistently associated higher bedding bacteria counts (BBC) with greater bacterial loads on teat skin and increased risk of intramammary infection, including clinical and subclinical mastitis.
The pathogen groups of greatest concern include coliforms, Klebsiella spp., environmental streptococci and strep-like organisms, and non-aureus Staphylococcus spp.
For green, or raw, RMS, the concern is that the material is already contaminated before it reaches the stall, and its organic nature can support additional bacterial growth. Studies generally find higher bacterial counts in RMS than in inorganic bedding, such as new sand.
Godden says producers switching from conventional bedding to raw RMS have historically reported increases in somatic cell counts and clinical mastitis. The question is whether processing can change that equation.
How Processing Affects Recycled Manure Bedding Bacteria
For years, some producers using processed RMS reported better udder health, but formal research lagged behind adoption of the technology.
“We didn’t have any data, no formal studies,” Godden explains. “It was all just testimonials from early adopters of the technology.”
Godden and colleagues at the University of Minnesota have since conducted observational studies examining different approaches to processing RMS, including anaerobic digestion, hot-air drying and drum composting.
The results suggest that the processing method is very important.
Anaerobic digestion can reduce some mastitis-associated bacteria, particularly coliforms and Klebsiella, but it is less effective against environmental streptococci and strep-like organisms, which are also important mastitis pathogens.
The reason may be related to temperature. In U.S. systems, manure typically moves through the digester over two to three weeks at approximately 100°F. That can reduce some organisms, but does not provide the same heat treatment achieved through dedicated drying or drum composting.
“It actually doesn’t work as well as you would hope,” Godden laments.
In a pair of University of Minnesota studies using 29 freestall facilities in Minnesota and Wisconsin, researchers compared green, digested, drum-composted and dried RMS. Farms were visited in summer and winter, with researchers collecting bedding samples for bacterial culture and dry matter testing along with herd health and management data.
Hot-air drying and mechanical drum composting consistently reduced BBC compared with green RMS. Digestion reduced coliforms and Klebsiella, but did not significantly reduce Streptococcus-like organisms compared with green solids.
The differences extended to udder health. Herds using dried or composted RMS had better measures of udder health than herds using green or digested solids, including lower measures of intramammary infection and chronic high linear scores. There was no significant difference in clinical mastitis rate among processing groups.
Because these are observational studies, the findings do not prove that one processing system will prevent mastitis. They do, however, provide evidence that processing can substantially alter the bacterial environment cows are exposed to.
Why Some Dairy Farms Using Recycled Manure Bedding Have Better Udder Health
RMS herds tend to have higher bedding bacterial counts and poorer udder-health measures than herds using other bedding materials. But that doesn’t describe every farm. In a 168-herd study, some farms using RMS had relatively low BBC and good udder health.
That variation suggests management plays an important role.
The first goal is producing clean, ready-to-use bedding. For RMS, dry matter is one important indicator. Godden’s recommended target for ready-to-use RMS is 35% to 50% DM. Bedding below 35% DM is considered too wet, while extremely dry material can create dust and other management problems.
In literature, the proportion of RMS samples with high coliform counts is substantially greater when bedding has less than 35% DM.
Monitoring Recycled Manure Bedding for Mastitis Risk
Bedding culture can give veterinarians another tool for investigating mastitis problems and establishing a baseline for herd monitoring.
“If you haven’t been routinely culturing, but you’ve got some mastitis problems going on and you’re trying to troubleshoot a mastitis problem, one of the steps in your investigation might be to culture the bedding and just see if you can rule that in or rule that out as a contributing factor,” Godden explains.
The goal is similar to routine bulk-tank culturing: establish a baseline so changes can be detected before they become a larger herd problem.
For ready-to-use RMS:
- Coliforms: Considered low at 10,000 CFU/cc or less; high at more than 200,000 CFU/cc
- Streptococcus-like organisms: Considered low at 500,000 CFU/cc or less; high at more than 2 million CFU/cc
Sampling should also be consistent. Godden recommends collecting samples from multiple pens rather than relying on a single location and using a standardized approach so results can be compared over time.
Managing Recycled Manure Bedding in the Dairy Stall
Even processed bedding can become contaminated after it reaches the barn.
Godden recommends getting fresh RMS into stalls as quickly as possible after processing, ideally within 24 hours, because bacterial populations can increase while material sits in storage. Once bedding enters the stall, frequent addition of fresh material and removal of contaminated bedding become important.
Stall management, manure removal, stocking density and ventilation also influence how quickly bedding becomes contaminated.
Processing lowers the starting bacterial load. Management determines how long that advantage lasts.
What to Consider Before Recommending Recycled Manure Bedding
The decision to use RMS should begin before a producer invests in processing equipment.
“The first conversation I’d want to have with the producers is ‘do you understand that this is a risky bedding material to adopt?’,” Godden says.
For herds where maintaining a very low somatic cell count is a high priority, Godden recommends thinking carefully before switching to green, or raw, RMS.
“If you are used to having low mastitis and clinical mastitis rate; if you’re used to having a low somatic cell count, and if that is a priority for you, then you might want to think twice about adopting a green or a raw recycled manure solids bedding system,” Godden says.
She makes the potential consequence especially clear with a hypothetical example:
“If your cell count is 100,000 today, it’s likely going to be over 200,000 within six months of adopting the system.”
That statement is Godden’s assessment rather than a quantified prediction from the studies, but it underscores the risk she believes producers should consider when adopting raw RMS.
For farms that choose recycled manure bedding, the current evidence points toward drying or drum composting as more effective approaches for reducing bacterial loads and supporting udder health than anaerobic digestion alone. Combining digestion with secondary drying or drum composting may provide greater reductions in bacterial counts.
Recycled manure bedding may offer economic and sustainability advantages. But the material going under the cow needs to be clean and appropriately dry, and the farm needs a plan to keep it that way.
The question isn’t simply whether recycled manure bedding can work. It’s whether the farm can manage the system well enough to make it work.
