Where now in using recycled manure solids as bedding?

Published 25 June 14

Slurry separation technology is nothing new but the way it can be used is, with new improved separators capable of producing material at dry matter levels of 34-38%. As a result, interest in the separation of manure to produce cattle bedding is increasing in Great Britain – but is it safe, or even permissible, within current regulations?

A recent DairyCo-funded scoping study has tried to shed further light on the practical implications and R&D manager Dr Jenny Gibbons says it has thrown up some interesting findings…

The perceived advantages of using recycled manure solids (or ‘green bedding’) as cattle bedding include improved cow comfort, lying times and cow cleanliness, and reduced costs. However, potential risks to both human and animal health need to be considered. In particular, the EU animal by-products regulation classifies manure as a Category 2 waste product and sets out permissible disposal routes for this material – of which animal bedding is not one, unless its ‘safe use’ can be demonstrated.

Since summer last year, DairyCo has been keeping farmers informed about developments.

In September 2013, DairyCo commissioned a scoping study through QMMS Ltd, The University of Nottingham and The Dairy Group which aimed to assess the potential risks and benefits of using recycled manure solids under British conditions, by gathering the available evidence from around the world.

It was hoped this would help Government regulators make a decision about whether any risks could be sufficiently mitigated to authorise its use. In a constructive move (and in light of increasing uptake of the technology), UK regulators agreed they wouldn’t enforce the regulation while the scoping study was being conducted.

Now the study is complete, the benefits to cow comfort and the potential cost-savings are apparent, but the potential risk to herd health is also evident. The report highlights that much of our existing knowledge on the subject has been acquired through practical experience and case study rather than rigorous scientific investigation. In particular, there is a general lack of robust information in relation to the presence of different pathogens, their survival and replication in various bedding materials.

Diseases which could cause concern and have been studied include mastitis, salmonella and Johne’s disease, but mastitis is the only disease that has been studied in any detail. There are anecdotal reports of serious outbreaks of clinical mastitis, including some fatal cases of Pseudomonas, and increasing cell counts. However, these reports are outnumbered by reports of successful use.

It’s also clear where poor practice has led to problems – for example, some episodes have been linked to cases where the bedding hasn’t been dry enough, others to cases where waste milk has been included in the slurry for separation.

To date, there are no reports on the microbial population of raw slurry before and after separation. Several studies have been conducted to investigate the impact of various treatments - including composting, anaerobic digestion, drying, heating and altering pH, on restricting bacterial growth.

Manure solids from anaerobic digestion is the most common source in the US, unlike in GB where fresh manure solids are used without any heat treatment. In general, pathogen levels are considerably reduced but the temperature in the digester is critical, and temperatures between 30-38°C can actually increase bacterial numbers. Further drying, for example, with fans or other heat treatment, is likely to reduce risks of disease spread, but it will also increase the cost of the operation.

Studies in the Netherlands and further afield have demonstrated that the use of acid or lime has a short-lived effect on bacterial growth, so it should not be assumed that the use of lime or acid protects the cow against disease risks.

For the report, the experiences of 19 British dairy farmers with an average herd size of 413 cows (ranging from 180 to 1,200 cows) were gathered by telephone survey. The three most common reasons given for using recycled manure solids as bedding were cost, cow comfort and difficulties with supply of alternative bedding materials.

Operating a recycled manure solids system has economic benefits too, according to calculations carried out in the report; these are largely dependent on cow numbers and on the finance arrangements for the equipment. For example, indicative costs are in the order of 71p/cow/week with a 400-cow herd, which can be compared with sand (140p/cow/week), straw (160p/cow/week) and sawdust (75p/cow/week); but on a 200-cow herd the cost of bedding with manure solids increases to 130p/cow/week. These calculations are based on a number of assumptions and on autumn 2013 prices, and will be individual to each farm situation. 

Studies have demonstrated a clear benefit to cow comfort, with cows lying down for longer, especially in the transition from a mat or mattress to deep-bedded cubicles using manure solids bedding. Longer lying times can lead to fewer lameness problems, better health and improved production. Anecdotally, cows are often described as ‘cleaner’ than on their previous bedding. Cow cleanliness and hygienic milking routines are an essential part of management on all dairy farms, and extra attention to these areas is required on farms using recycled manure solids.

As far as food safety is concerned, recycled manure solids is a potential source of bacterial contamination of raw milk. The spores of certain bacteria, particularly those that are heat-resistant are encouraged by composting.. Too high a concentration of spores can lead to losses during the manufacture of cheese and reduce the shelf life of pasteurised milk. Recently, in the Netherlands, farms composting manure solids have shown high levels of spore-forming bacteria in the bulk tank milk, which has led to a restriction from one milk buyer on its producers composting the bedding material before use.

In summary, there are still lots of unanswered questions and much to learn on how to mitigate the potential health risks.

Recommendations were made in the report for risk management, based on current interpretation of best practice. The evidence gaps need to be filled before definitive conclusions can be drawn on the safe use of recycled manure solids as bedding. While a proportion of these gaps could be addressed in a medium time scale, several would require longer term perspectives (for example, the risk of developing antimicrobial resistance).

After consideration of the initial report, the policy position of Government regulators is to adopt a precautionary approach which will allow the use of manure solids as bedding, but ONLY under a set of prescribed and controlled conditions. This is to allow a further period of data collection for the gaps in knowledge and evidence to be addressed. At the time of writing, discussions are underway between Defra and industry bodies to finalise the conditions to which users will be expected to adhere.

The scoping study only addressed scientific issues. However, the supply chain is acutely aware of the potential negative public reaction to the use of recycled manure solids as bedding. Taking a responsible, precautionary approach and by collating all the available evidence enables the facts to be presented.

However, it is also clear that should new research identify further risks to public or animal health that cannot be sufficiently mitigated, Defra may no longer permit the use of manure solids as bedding material under the EU Regulation.

Several parties are active in the marketing of the slurry separators suitabale  for making bedding. These have actively been engaged throughout this process and have agreed to demonstrate and communicate best practice guidance to farmers. But the successful adoption of this technology will end up being largely determined by dairy farmers themselves  – who will need to act responsibly in light of the opportunities and associated risks.

There is widespread recognition of the intrinsic importance of getting this right. It is believed that an approach based on robust data collection to inform best practice, but most importantly to safeguard the reputation of our industry, is the correct way to proceed.

Further up to date information on recycled manure solids, download the executive summary of the report.