Manure solids for bedding: A viable option?

Marcia Endres, Extension Dairy Scientist

February 15, 2008

Organic bedding materials are getting more difficult to obtain. As a result, there has been recent interest in the upper Midwest in using recycled manure solids for bedding. At the recent annual National Mastitis Council meeting in New Orleans, there was a session on bedding management – using recycled manure. Presenters included Kenn Buelow, a producer veterinarian from Wisconsin; Peter Ostrum, a veterinarian from New York State; and myself. My goal as the first presenter was to give an introduction to the topic. Manure solids have been used for a long time in Western U.S., where the more arid climate allows dairies to successfully utilize separated manure solids in freestalls and lots. However, in the more humid climates of the Midwest and Northeast U.S., there has been more reluctance in using separated manure solids due to concerns with possible increase in mastitis incidence. Improved separator and methane digester technology has attracted producers to use separated solids for bedding. The impact on milk quality and udder health has varied from good to bad. It is not yet clear why some dairies have succeeded and some have failed with separated solids.

One example I presented at the conference was a recent field study conducted by Dan Meyer and colleagues at Iowa State University. They worked with a 700-cow freestall dairy in Iowa that had used a digester since 2001. A separator was installed in early 2006 when their project began. Two additional neighboring dairies received free bedding in exchange for allowing the researchers to sample their freestall bedding, manure and milk. All three dairies bedded stalls about once weekly. Dry matter content was 34% and 40% for fresh and composted solids, respectively, but was 72% when used in the stalls. Gram-negative and streptococci bacteria counts were reduced three log-scale, and coliform counts were less than 100 colony forming units/gram (cfu/g) after manure was digested. Bacteria counts were further reduced if the solids were composted and the temperature exceeded 140° F. All bacteria counts increased 10,000 to 1,000,000 in stalls during the first 24 hours after bedding addition and remained at the same level between bedding additions. Somatic cell counts (SCC) on all three dairies remained the same or decreased. There was no increase in clinical mastitis cases. Authors indicated that all producers participating in the project were satisfied with the manure solids and will continue to use it for bedding.

Kenn Buelow, who owns and operates two large dairies in Wisconsin, has also had mostly positive experiences using digested separated solids in his freestalls. One of the dairies averages about 185,000 SCC and the other that has mostly first-calf heifers, averages about 100,000 SCC. They have excellent bedding management, with stalls cleaned at every milking and bedded 2 to 3 times per week depending on bedding level. They use intramammary dry cow and incoming heifer treatment. Teat sealant is also used. They practice excellent cow prep procedures at milking time. Kenn mentioned that possibly the type of digester used can make a difference in the type of bedding material obtained. They use two plug-flow digesters at each dairy, which are maintained at 100° F with 22-day storage capacity and the ability to stir the digester with gas diffusers. This results in a homogeneously heated product. He thinks the material leaving their digesters should be lower in rapidly digesting energy substrate than if using just separated solids or digested solids that don’t reach the temperature and residence time they do with the plug-flow type.

Peter Ostrum related an experience they had with a large commercial dairy in New York State. They replaced their recycled sand bedding with dried manure solids for a period of approximately one year. Manure solids in this case were not from a digester, but separated from the effluent coming from the barn with the resulting pile left to heat and used for bedding within three weeks of storage. They observed a dramatic increase in coliform mastitis (primarily caused by Klebsiella). Various attempts were taken to reduce the risk of clinical mastitis to no avail. Monthly cull rates almost doubled during this time. The dairy decided to discontinue the use of manure solids. After sand was reintroduced, clinical mastitis rates and SCC returned to what they were prior to using manure solids. Needless to say, their experience with manure solids for bedding was not a good one.

Is it the type of manure solids used? Digested, separated, composted? Bedding and milking management? We don’t have a definite answer, but it appears that manure solids can be used successfully by some producers. It might become a more common option in the future. Are cows comfortable? Producers indicate that cows like stalls bedded with solids. So, we help cow comfort but maybe have more challenges with milk quality and udder health. However, it might be possible to make it work on that aspect too, especially if using digested solids combined with excellent bedding and milking management.