Compost barns: Success takes work

Reproductive performance, foot health and culling rates appear to be the biggest winners for dairies that converted to ‘compost’ barns, but the facilities require good management to overcome other challenges.

by Susan Harlow

Whether a larger producer seeking more comfortable special needs housing, or a smaller dairy wishing to expand or upgrade cattle housing, a compost bedded pack dairy barn may be an alternative. University of Minnesota dairy scientists warn, however, that this isn’t loose housing from days gone by –- good management is necessary to make the system work.
Marcia Endres, with the University of Minnesota’s department of animal science, and her graduate student Abby Barberg studied 12 compost pack barns. The herds averaged 74 cows, and all except one herd previously housed cattle in tiestalls.
Dairies showed benefits from the change, including higher milk production, better foot and leg health, more freedom of movement for cows, and, possibly, better herd social interaction. But sawdust bedding –- cost and availability –- was a big concern.
Endres’ research found:
• Milk production increased substantially in the new barns, an average of 2,105 lbs. per cow per year, although other factors may have contributed. Milk yields were higher than in the tie-stall arrangements, but not necessarily higher than they would have been in comfortable, sand-bedded freestalls.
• Hygiene and body condition were similar to that of cows in other types of barns.
• More than half of the dairies –- 57% –- showed an increase in heat detection rates.
• 71% of dairies increased pregnancy rates, improving from an average of 13.2%, to an average of 16.5%.
• Average herd turnover rates dropped from 25.4% to 20.9%.
• SCC averaged 325,000, about the same as Minnesota’s statewide average. About 67% of the dairies reduced mastitis infection rates in the compost barns, but only 43% showed a significant drop in bulk tank SCC, which averaged 261,000.
• Foot and leg health was good. Nearly 8% of cows were clinically lame, compared to about 25% reported in freestall barns and 19.6% in tiestalls. About 75% of cows had no hock lesions.
• Pneumonia and eye irritation were sometimes problems, caused by dust when too much sawdust bedding was added at one time.

General construction
Most barns in the study were constructed like three-row barns, with concrete feed alleys. Bedded packs were built on clay bases surrounded by 4-foot perimeter walls. The walls between the feed alley and pack had two or more walkways for cows and equipment to pass through.
To remove heat and maintain a dry bedding surface, excellent ventilation is a must. Sidewall height is recommended to be higher than that for a freestall barn to accommodate the lost space of the sidewall opening due to the manure pack walls. Half of the barns studied had 14-foot sidewalls, and the other half had 16-foot sidewalls. Some with the 14-foot sidewalls said they would go to 16-foot sidewalls for their next barn to provide better access for bedding trucks.
The barns had 3-foot eave overhangs to minimize roof runoff and rain being blown onto the bedded pack.
Open ridges ranged from 1 to 3 inches per 10 feet of building width. Mixing fans are important to blow air downward toward the middle of the composting bedded pack. They need to be hung high enough to provide room for stirring equipment at the maximum bedded pack height.
Waterers located in the feed alley must be separated by distance or a wall from the composting bedded pack to minimize wetting the pack and keep waterers cleaner.

Managing the pack
Producers started out with a clean pack in the fall, bedded about 1 foot deep with dry shavings or sawdust. The bedded pack is actively managed to rapidly compost the manure and urine. Microorganisms, including bacteria and fungi, break down organic matter into simpler substances.
The effectiveness of the composting process depends on environmental conditions present within the pack, including oxygen, moisture, temperature, amount of organic matter and the size and activity of microbial populations. Essential elements include carbon, nitrogen, oxygen and moisture. If any of these elements are lacking, or if they are not provided in the proper proportion, microbial activity will be hindered, and the compost will not generate adequate heat.
Achieving high temperatures within the pack is important to killing pathogens and keeping the pack surface dry. Temperature is directly proportional to the biological activity within the composting bedded pack. As the metabolic rate of the microbes accelerate, the temperature within the bedded pack increases. Maintaining a temperature of 130 F or more for three to four days favors the destruction of weed seeds, fly larvae and pathogens, and conversion of odor- and pathogen-free organic matter into compost.
Herds in Endres’ study added a load of sawdust every two to five weeks. The packs were aerated to a depth of 8 to 10 inches when cows were being milked, a job that took about five to ten minutes. Producers used chisel plows, aerators or roto-tillers to turn the compost, drying it out and creating a fluffy surface. “That made the system work,” Endres said.
Endres recommends 80 to 85 square feet of space per cow for Holsteins, and 60 to 65 square feet for Jerseys in the bedded pack area.

Bedding costs higher
Bedding costs averaged about 60¢-80¢ per day, three to eight times more than it costs to bed freestalls, Endres said.
Some material was removed in the spring; all of it was taken out in the fall and spread on fields or sold as compost. But temperatures in the pack weren’t high enough to get rid of pathogens sufficiently for good compost, Endres said. The bedding would have to be finished off at higher temperatures first.
Udder health and milk quality are still question marks, Endres said. Although bacteria counts in the bedding material were high, udder health and milk quality weren’t necessarily compromised. “We found a lot of mastitis pathogens in the bedding –- a lot of exposure –- but not necessarily infections,” she said.
Dairies must have excellent milking preparation procedures and healthy teat ends to make the compost pack barn work.

Table 1.
Analysis of bedding samples in compost barn study
Recommended
Average         Range                 for compost
Temperature, F                   108              76-138                  130-150
Moisture, %                        54.4             28-78.9                   50-60
pH                                      8.5              6.5-9.9                    6.5-8
Nitrogen, %                       2.54              0.57-4.22                   NA
Phosphorus, ppm             3,247            378-6,668                  NA
Potassium, ppm             15,270          2,568-29,570                NA
Carbon:Nitrogen ratio    19.5:1             10.9-87.5               25:1-30:

FYI
■ Marcia Endres is an animal scientist at the University of Minnesota. Contact her via e-mail: miendres@ umn.edu, phone: 612-624-5391, or visit
to www.extension.umn.edu/dairy.

■ The University of Minnesota Extension dairy team publishes a quarterly Compost Dairy Barn Newsletter. To view archived copies, visit www.
extension.umn.edu/dairy/management/compostbarns.htm.

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