Compost barns: What have we learned so far
Published in Dairy Star January 14, 2006
I think that by now all of you have heard or read about compost dairy barns. Many more were built this past year in Minnesota. There are still questions about these barns. Therefore, we at the University of Minnesota decided that the first step to learning more about how compost barns were functioning was by interviewing producers using the system. During this process we also collected bedding and milk samples, observed and evaluated cow behavior, summarized cow records, and scored cows for locomotion, body condition, hygiene and hock lesions. Our goal was to collect some hard numbers on cow comfort and udder health related aspects, bedding characteristics, facilities, etc. Follow-up studies are planned that will address some of the concerns raised during the study we conducted.
Following are some preliminary results of our study:
Some herds have been able to achieve low levels of somatic cell counts (SCC) in this system. The chart below shows a SCC range on 11 farms from 200,000 to 650,000, with an average of 325,000. So there is still room for improvement. Excellent cow prep milking procedures are a must, especially with a compost dairy barn facility. Bedding bacterial counts averaged over 9 million colonies/mL with some culture results as high as 23 million. It is also important to aerate the pack at least 2 times per day to eliminate cow pies and dry the bedding surface.
Most producers mentioned cow comfort and longevity as the main reasons to adopt this housing system. We scored cows for locomotion and hock injuries as indicators of cow comfort. We also observed and recorded cow lying behavior; however, those results are not summarized yet.
In relation to hock injuries, we were pleased to find that only 0.97% of cows had swollen hocks. That compares with 1.8% for sand stalls and 14.1% for mattress stalls in a study we conducted last year. Even more dramatic are the results we found for lameness prevalence. Only 7.8% of the cows were lame, with 2 herds having no lame cows at the time of our visit. That compares very favorably to 24.6% lameness prevalence in a study we recently conducted with cows housed in free stalls. This is a strong indication that cow comfort is improved in compost dairy barn facilities.
One concern expressed by some producers and their veterinarians was the presence of dust which could cause eye irritation or pneumonia. This raises the question about air quality in these barns and, therefore, our team has submitted some grant proposals for follow-up studies that will include air quality analysis.
For the producers we interviewed, bedding availability was their main concern. Most producers inquired about what other sources of bedding besides sawdust could be used. We plan on conducting follow-up studies to investigate what other materials could work. We have been contacted by a couple of dairy producers who are using ground soybean straw with success. One of the producers indicated that the material is actually less dusty than sawdust and it can be stirred as well as sawdust. Our University of Minnesota agronomists and soil scientists were concerned about the removal of straw from the fields and the resulting negative carbon credits. One of the soil scientists also cautions that, "with soybean straw it is not recommended harvesting it from sloping fields, since there would be nothing left to protect the soil from erosion."
In summary, results so far have shown that compost barns can be a very good alternative for housing dairy cows. Like any system, they require optimum management to work properly. Special attention should be given to milking prep procedures and maintenance of minimum space per cow (ideally more than 85 sq. ft/cow) to avoid high levels of somatic cell counts.
These results are part of a presentation during the annual Minnesota Dairy Days held in January at nine locations around the state. The results will be posted in our website (http://www.extension.umn.edu/dairy/dairydays06) in the near future. If you have any questions, please feel free to contact me.