using dried digestate as bedding

Published 31 March 15

As many will know, the use of recycled manure solids (RMS) as bedding has been agreed by Defra and Scottish Government, while further data is collected under prescribed management conditions. This research is currently ongoing.

However, while latitude has been granted on RMS, this has not been extended to the use of AD digestate solids for bedding. RMS refers to raw slurry passed through specialised slurry separation technology, to produce a fibre product with dry matter levels above 34%. This fibre is used for cattle bedding. Digestate solids are produced after raw slurry is passed through an anaerobic digester (AD) to produce a nutrient-rich slurry called digestate. Next, the digestate is passed through a slurry separation unit to produce a fibre product. This fibre can be dried using the heat generated from the AD.

The use of digestate solids or dried digestate solids as bedding is not currently permissible in the UK. This arises from particular concerns in the Netherlands over the generation of heat resistant bacterial spores during the composting process of composted bedding materials.

In the Netherlands, composted bedding materials includes any bedding materials that are composted to 70°C for 60 minutes before being distributed as bedding for dairy cattle housed in deep bedded yards or cubicle sheds. A recent Dutch study reported the use of compost and it was found that composted bedding materials had detrimental effects on concentration of heat-resistant spore forming bacteria. An increase in spores was reported in both composted bedding material and in bulk tank milk from farms using composted bedding material compared to sawdust bedding. The bacteria spores are very heat resistant (up to 100°C), can survive pasteurisation and adversely affect milk quality. For this reason, from January 2015, Dutch milk processors no longer accept milk from farms using composted bedding material.

The reason for the continuing moratorium on AD digestate solids is that the same concerns hold for the heat produced during anaerobic digestion. To date, there is a large gap in the scientific literature of research conducted on the use of this as bedding.

DairyCo is currently in discussions with the AD industry regarding research in this area and we hope to start investigations the summer of 2015. If you are aware of any ongoing work, please let me know ( Many unanswered questions remain but, hopefully, we are on our way to providing some of the answers through current and planned research.

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