However, proper barn design and excellent daily management are essential for successful composting and to avoid negative animal health outcomes. A successful CBP begins with three key principles: bedding, stocking density and airflow.
Bedding
In a CBP barn, bedding is more than an absorbent lying surface for your cows. Bedding acts as the carbon source, or essentially food, for the microorganisms within the composting bed. Before deciding to construct a CBP barn, consider where and at what cost you can acquire a continuous supply of bedding material. A mixture of kiln-dried sawdust and shavings remains the “gold standard” for CBP bedding. Other bedding alternatives exist, though may require more frequent additions and result in less efficient composting. Moisture content (and not time) determines when additional bedding needs to be added. The CBP should be between 45% and 55% moisture. To quickly test moisture, grab a handful of compost material and squeeze it. If water drips out of the ball, the CBP is too wet and you should add more bedding. If the material cannot form a ball, the CBP is too dry and you can wait before adding more bedding.
Stocking density
Animal numbers can fluctuate on a dairy. A CBP is not always forgiving to those fluctuations. Stocking rates in a CBP are driven by the urine and fecal outputs of the cows. Producers should aim to provide 125 to 150 square feet per Holstein cow. Smaller framed cows, such as a Jersey, require less space. Overcrowding the barn results in too much moisture, dirty cows and potential for udder health consequences. High stocking rates can also pack down the CBP, restricting air flow to the microbes and reducing composting efficiency. When planning the footprint of the barn, design for the peak number of animals and not the average to ensure adequate space year-round.
Airflow
The aerobic composting process requires oxygen. Adequate airflow is not only important for cow health and comfort, but also to feed air into to the CBP. Designing the barn with high sidewalls and fans provides natural and mechanical ventilation. Proper ventilation ensures microbes are supplied adequate oxygen essential for proper composting. Limiting the air available to microbes can reduce or stop composting. Twice daily stirring of the pack (without fail) is also essential for composting success. A field cultivator accomplishes deep aeration (10 to 12 inches). A rototiller provides more shallow aeration (6 to 8 inches) with more breakdown of larger compost chunks and a more uniform surface.
Key points
- Is there a source of year-round bedding material that is affordable and consistent?
- Add additional bedding based on CBP moisture content.
- Provide 125 to 150 square feet per cow (Holstein; less for Jersey).
- Design the barn for peak animal numbers.
- Stir the pack twice daily, without fail!
- Ventilate barn with natural and mechanical ventilation to ensure an aerobic environment for composting.
—Excerpts from California Dairy newsletter, August 2019
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Randi Black
- Agriculture and Natural Resources
- University of California
- Email Randi Black
PHOTO: A successful compost-bedded pack barn begins with three key principles: bedding, stocking density and airflow. Photo courtesy of the University of California.
