Compost-bedded pack barns have gained appeal in many parts of the world as an alternative to stall-based dairy cow housing methods. Compost-bedded pack barns are loose housing barns that give resting room by decomposing manure and organic bedding.

A compost-bedded pack barn differs from a traditional-bedded pack barn. Its bedding is constantly tilled or disturbed to increase microbial activity, which leads to composting and bedding drying. For best composting results, stir the bedding two to three times per day.

Most compost-bedded pack barns in the United States use sawdust or wood shavings as a carbon source. Adding carbon to the manure to obtain the carbon-to-nitrogen(C-N) ratio required for composting. Compost-bedded pack barns offer exceptional cow comfort by allowing cows to lie down and rise freely without stall restrictions. However, to get the intended effects, compost-bedded pack barns must be properly built and operated. Over the previous decade, we have learned a lot about what makes these barns successful or unsuccessful, as many of the issues and failures are related to sub-optimal lighting and air movement.

Bunching behavior: 

Light or air problems frequently result in bunching or grouping behavior in all dairy facilities, but this problem is worsened in compost-bedded pack barns. Bunching behavior is noted when cows gather or bunch together in one barn area and avoid the remaining areas. In extreme cases, cows may only use 10-20% of the available space.

Bunching behavior is more intense and evident in compost-bedded pack barns due to fewer physical barriers separating the cows. Heat stress, flies, light, and air all contribute to bunching behavior. The influence of pack heating on resting behavior is another potential contributor to bunching behavior in compost-bedded pack barns.

Although the surface temperature of a compost-bedded pack barn is close to ambient, it is uncertain how compost heating influences laying behavior in hot, humid situations. Anything we may do to lessen heat stress or the fly population may diminish the occurrences of bunching behavior.

Barn orientation and light: 

The natural light patterns within a dairy barn get significantly influenced by barn orientation. An east-west orientation permits the least sunlight into a barn. The sun goes over the top of the barn in an east-west direction throughout the day. In contrast, with a north-south configuration, the sun moves over the larger sides of the barn, creating higher light intensity in the cows' resting or eating areas.

Cows will move away from regions with more light and toward darker parts of the barn under heat stress. Cows are far more sensitive to minor variations in light intensity than humans, and they connect darkness with shade. Of course, there are times when light can be an issue for any orientation. However, the east-west direction results in a far lesser proportion of the day when lighting intensity can impair cow distribution.

Bunching behavior in compost-bedded pack barns is far more common and severe in north-south than in east-west barns. When building a new compost-bedded pack barn, an east-west orientation is preferred. This problem may be avoided in north-south barns if feed bunks are placed on the barn's outer walls rather than in a drive-through configuration.

Additional lighting considerations: 

Eave overhangs can help to address some of the issues with light intensity. Eave overhangs, should be one-third the height of the sidewall, can help provide some shade and rain protection. Shade cloth can help, but use caution as even  porous shade cloth obstructs airflow. Take care not to inadvertently create an air flow problem while resolving the sunlight heat.

Artificial light can also be utilized as a supplement to lessen light fluctuation and optimize cattle distribution. 20-foot candles can offer the appropriate light level for dairy cows (200 lux). A digital light meter can be used to measure the intensity of light within a barn. You can also download free light meter apps for your smartphone for demonstration purposes. Keep in mind that these apps are likely to be less precise than light meters. You can use a light meter to determine which regions of the barn have lower light intensity. You can install artificial lighting (preferably, LED) to better distribute light within the barn. Wiring the lights so that portions can be switched at different times allows you to level out the light intensity in darker areas of the barn.Uniform light intensity throughout the barn seems to reduce bunching.

Ventilation and barn design:

Natural ventilation, assisted by mechanical ventilation, is used in most compost-bedded pack barns. The barn must be properly built to promote natural ventilation. The heat and moisture produced by the cows and the composting process are removed by ventilation. Ventilation is crucial in compost-bedded pack barns. Not just for cow cooling but also for pack drying.

Side walls must be at least 12 feet taller than the retaining wall or outside curb. For barns wider than 40 feet, a height of 14 feet is recommended. For example, a 100-foot-wide barn with a 2-foot concrete wall should have a total side wall height of 16 feet. For manure storage and to maintain the bedding within the structure, early compost-bedded pack barns featured 4-foot retaining walls. However, practical and computer-modeling experiments have shown that 4-foot retaining walls prevent air from flowing onto cows lying down. It is recommended that a 2-2.5-foot retaining wall be used instead.

To enhance natural ventilation rate per cow, the ideal roof pitch is 4/12. A large barn's overly flat roof hinders natural ventilation and can quickly create warm, wet air pockets. It is recommended to have a continuous ridge vent opening. A least 3 inches width for every 10 feet of roof width, with a minimum space of 12 inches for barns less than 40 feet wide. Air enters the barn via the windward sidewalls and exits via the ridge vent and the leeward wall aperture. Ridge vents work best when the prevailing winds are perpendicular to the ridgeline.

Fans:

Circulation fans, either ceiling or panel-mounted, are recommended to keep the pack dry and to guarantee proper airspeeds throughout the barn. Many farms have high-volume, low-speed (HVLS) ceiling fans installed in their compost-bedded pack barns, which appear to perform effectively. When installing fans, ensure there is adequate clearance underneath for tillage equipment to work at maximum pack depth and that the fan blades do not damage the barn trusses. Most compost-bedded pack barns incorporate sprinklers with panel fans over the feed bunk for evaporative cooling in addition to fans over the pack area.

One of the most common problems in compost-bedded pack barns is insufficient or poorly placed fans. Because the area per cow in a compost-bedded pack barn is substantially larger than in a free stall barn, fan installation and maintenance costs may be regarded the compost-bedded pack barn's largest drawback. Furthermore, in a compost-bedded pack barn, the entire space must be addressed, although in a free stall barn, fans in alleyways are often not an issue.

Unfortunately, decisions regarding fans in compost-bedded pack barns are frequently made after the barn has been built. Instead, they should be considered during the design of the new barn as well as the primary decision of whether to create a  compost-bedded pack barn or a free stall barn. We see barns all the time that could be spreading air much more efficiently if the barn proportions had been modified to better fit fan needs.

Regardless of the type of fans chosen, taking into account spacing is vital to minimize dead spots. Dead spots in a compost-bedded pack barn cause an uneven distribution of cows and lead to bunching behavior. Cows will eventually reveal the location of the fans; they will lie in rows in front of panel fans and incircles beneath HVLS fans. The purpose of using fans is to achieve air flows of 400-600 feet per minute (5-7 miles per hour) at cow level. HVLS fans have the advantage of covering a bigger area per fan, being more energy efficient, and being able to run at lower speeds during the winter. Even at top speed, they may only achieve the bottom limit of the needed air speed to cool cows. Panel fans, on the other hand, readily achieve the recommended air speeds - but the side-to-side spacing required for equal air dispersion necessitates a large number of panel fans.

It can be difficult to hang fans in the middle of a pack barn. HVLS fans should be spaced at least 2-2.5 times their diameter. A 20-foot HVLS fan, for example, will span 40-50 feet horizontally and vertically. Manufacturers may recommend 3-4 times the diameter space, but this is insufficient for optimal cow comfort and is based on huge, factory-type buildings.

Panel fans should be spaced no more than 10 times their blade diameter width apart lengthwise down the barn. 48-inch fans, for example, should not be set more than 40 feet apart. Side-to-side space between fans should be 6-10 feet, and here is where most compost-bedded pack barns fall short. However, keep in mind that these are only suggestions; individual instances of fan spacing are determined by manufacturer rules and design elements.

Consider the recommended fan spacing for a 48-by-204-foot pack area. This barn would necessitate five 24-foot HVLS fans running along the center. The same barn would require four 48-inch fans across, with five fans in each row, for a total of twenty 48-inch fans. Both configurations should effectively cover the pack area. Different operations may make different judgments based on purchase costs, electricity costs, and personal preferences.

Finally, regardless of the type of fan used, it is critical to understand how many fans are required from the start. Bedding availability, fan purchasing and electricity cost are some of the essential factors to consider when considering whether to build a compost-bedded pack barn.