Does RMS bedding deteriorate milk quality or udder health?
Risks, benefits and optimal management of recycled manure solids for use as bedding.
The use of recycled manure solids (RMS) as bedding in dairy operations offers significant advantages in terms of comfort and overall costs. Animal by-products (ABPs), however, have the potential to spread animal disease. If not properly disposed of they can be dangerous to both animal and human health.
Within the European Union, there are rules that regulate the movement, processing and disposal of ABPs. Under Regulation (EC) 1069/2009, ABPs are categorized according to their risks; recycled manure solids fall under a section for ‘technical use’. Many dairy farmers have enquired about the use of RMS for bedding. Does its use increase the risk of disease? It’s a good question, and one that has motivated several research projects.
AHDB Dairy (formerly DairyCo) commissioned a scoping study in 2013. At that time, researchers concluded that more data was needed in order to properly assess the potential risks of using RMS for both public and animal health. In the meantime, the Department for Environment, Food and Rural Affairs (Defra) adopted a precautionary interim position, allowing for a period of further research. Their goal: to better understand the risks and benefits of using RMS bedding under conditions specific to the United Kingdom . Currently, under Defra’s precautionary position, RMS can only be used under a set of prescribed, controlled conditions.
In 2014, another research contract was awarded to Quality Milk Management Services Ltd (QMMS), The Dairy Group, University of Nottingham and Paragon Vets to conduct another study on the risks, benefits and optimal management of RMS as bedding for cattle. Andrew Bradley of QMMS in Wells, Somerset, was part of the team that conducted the new research. He presented his findings at the World Buiatrics Congress in Dublin, Ireland in July of this year. The Welsh Government funded the study.
According to Bradley, the key aims of the study were to assess the presence and levels of selected pathogens and milk spoilage bacteria in RMS bedding in comparison with other types of bedding. It also aimed to assess the transfer of pathogens and milk spoilage bacteria from different bedding types to bulk milk, and to determine potential mitigating factors. Finally, it aimed to provide information on the relationships between bedding and udder health in dairy cows under UK-specific conditions.
The study involved the collection and analysis of data from an epidemiological survey of 125 farms using RMS, sawdust and sand as bedding where 40 farms used RMS, 41 used sand, and 44 used sawdust. It also involved a controlled study of different bedding materials and depths, as well as an observational study of the different methods of initial build-up of deep RMS beds. Finally, the researchers collected and analyzed bulk milk samples, as well as a collation of udder health data. Samples were assessed for the presence and level of selected pathogens, including: total viable count (TVC), coliforms, Streptococcus spp., Staphylococcus spp., thermodurics, thermophilic spores, psychrotrophs, Bacillus cereus, Yersinia enterocolitica , Salmonella spp and Listeria spp.
“We visited farms and we timed that visit so that it would coincide with the longest period that the bedding was in use,” explained Bradley. “We would go to a farm just before the farmer was going to re-bed the cubicles. This also coincided with the collection of bulk milk.”
Bradley and his team sampled the old bedding just before the new bedding was put in. To create consistency, a system of sampling was established; at least ten cubicles per barn were sampled.
With the exception of Streptococcus spp., bacterial counts in “used” bedding were significantly higher in RMS than they were in sand and sawdust. Bradley notes, though, that there was often as much variation within bedding type as between bedding type.
Interestingly, though, despite the fact that there were high levels of bacteria found in the “used” RMS bedding, there was no association between bacterial count in bedding and in the bulk milk sampled on the same day. The same held true for all bedding types.
“Considering we’re taking recycled manure, which is essentially the fiber component of feces, to me it was surprising that there was more variation within beddings than between beddings in terms of the bacterial numbers,” said Bradley. “So as you might expect, while we typically saw RMS typically having the highest counts, when we considered, for instance, coliform counts, then the highest coliform count in bedding was actually on a farm with sawdust bedding, and yet the 15 farms or so with the lowest coliform counts were also bedded on sawdust.”
“Yet you tended to see the highest bacterial counts in recycled manure solids, “ he continued, “but some farms on the other bedding materials still managed to get to extremely high bacterial levels. That, in some respects, was surprising.”
Despite the fact that high levels of bacteria were found in “used” RMS bedding, bacterial counts in bulk milk did not differ from the groups of farms using sawdust or sand. There was also no association between bacterial count in “used” bedding and in bulk milk sampled on the same day, across all bedding types. Across all bedding types, the researchers found that fore-milking was associated with a lower total bacterial count (TBC) in bulk milk, but not with any other bacterial species or grouping. However, Bradley found that within the population of RMS farms, higher total bacterial count in “used” bedding was associated with higher total bacterial count in bulk milk.
Bradley also found that somatic cell counts in bulk milk were not significantly different between farms and bedding types. He did note, however, that SCCs tended to be lower on sawdust farms compared to the RMS farms. On RMS farms, Bradley notes that pre-dipping likely contributed to lower bulk milk SCC.
It likely comes down to teat preparation,” he said.
When milk quality was analyzed across all bedding, Bradley said there were no significant differences detected with the exception of Streptococcus spp and Staphylococcus spp counts. Interestingly, used sand was significantly more likely to contain Listeria spp, he said. In the controlled study, it was also more likely to be isolated from milk taken from cows bedded on sand than on RMS.
“I think the total lack of relationship between bacterial counts in bedding and bacterial counts in milk is not what one might expect – we didn’t find any correlation,” he said in an interview. “I can look back and think that that sort of makes sense, given that farmers will adapt their pre-milking routines to the bedding they use, but it’s not what you think when you start.”
“The other thing that we found really surprising was the amount of Listeria spp we found in the sand farms,” said Bradley. “We really didn’t expect that. We found it in the ‘used’ sand samples in the survey, but also in the fresh sand samples in the controlled trial.”
That discovery actually made Bradley and his team change sand sources mid-study in the controlled trial. Listeria, however, was found in the new sand samples as well. This surprised the researchers and made them question how often farmers were bringing pathogens onto the farm. “We know we can find Listeria in soil, but we didn’t really expect to find it in washed sand,” he said.
In the controlled trial, Bradley and his team also evaluated all cows for new intramammary infections or an apparent cure. There results showed significant variation between the bedding types (p=0.015). “New intramammary infections were significantly less likely to occur in cows on sawdust beds than on deep RMS (47/961 vs 84/965; p=0.012) or sand beds (47/961 vs 78/965; p=0.04),” Bradley wrote in his report for the congress. “No impact of bedding material on the likelihood of a quarter curing could be identified.”
During the 16 weeks of the study, Bradley found that a total of 10 cows had developed clinical mastitis. Most frequently, Klebsiella spp was the cause. He also found that cows bedded on RMS tended to be at a higher risk of developing clinical mastitis than cows not bedded on RMS.
In conclusion, the data suggests that there is not necessarily a relationship between the number of bacteria in bedding and in bulk milk. There is also no clear relationship between the number of bacteria in bedding and udder health.
With that said, management is important for mitigating bacterial numbers in bedding. Finally, when considering bedding types, Bradley said that fresh RMS, if properly managed, need not be associated with the deterioration in milk quality or udder health.
“Any bedding material can work if used properly,” he said. “I think recycled manure solids can work and do work on many farms, but I think they probably take a much higher level of management and there’s much more potential for things to go wrong.”
“If I was putting up a new dairy unit today and designing it, what bedding material would I use?” asked Bradley. “Personally, I would still choose sand.”
