Bedded Packs

There are currently two contrasting methods to managing a bedded pack barn: anaerobic fermentation and aerobic decomposition.

1. Anaerobic fermentation – Traditional bedded packs

Fresh dry straw is added daily to a bed which accumulates in layers over a period of 4 to 6 weeks before removal and replacement. The layers compact, become moist and decompose, removing oxygen from the bed, leading to an anaerobic fermentation. Deep beds of other organic bedding material such as sawdust are very difficult to manage from a bacterial growth standpoint, and such material is better put to use in composting systems. Sufficient bedding must be added to keep animals clean and dry. Sand bedded areas have been used by some farms successfully, where wet contaminated sand is removed daily and fresh sand added weekly.

2. Aerobic decomposition – Compost barns

Deep bedded packs using fine dry wood sawdust are composted by stirring twice a day to a depth of 8 to 12 inches (20 to 30 cm), with the aim of generating a minimum temperature of 140 °F (60 °C), sufficient to inactivate bacterial pathogens, weed seeds, and fly larvae. Moisture levels must be maintained between 40 and 65%.

Design considerations for all bedded pack barns

The basic design of these systems is very similar and must be targeted to prevent some of the problems associated with housing dairy cows on a large fermenting pile of organic material. The problems include:

1. Moisture

A bedded pack has a large amount of milk, urine, and fecal matter added to it each day. Drainage and the addition of adequate amounts of bedding are therefore very important. In addition, the air adjacent to the pack becomes very humid and contaminated with noxious gases such as ammonia, thus ventilation of the area is also of great importance.

2. Bedding damage by excess traffic

Cows must travel across the bedded pack as they move around the pen and move from the feed bunk to a place where they may lie down. This movement, if limited to entrance and exit points (gate openings), damages the bed in these areas and renders them useless as a lying area.

3. Access to water

Cows spill a large amount of water from the trough while drinking. It is vital to exclude access to water from the bedded area to prevent spoilage of that area of the pack. So waterers should be accessible from the concrete apron only and cut into the bedded area with a wall built around to limit access from the bedded pack side and to prevent splash from entering the bedded area, as shown below.

Waterer design and location in a bedded pack

4. Stocking rate (cows per square foot or square meter of bedded area)

Determines the quantity of manure and urine added per pound of bedding. If the area per animal is too low, bedding will probably not be added frequently enough to keep the resting area dry.

With these problems in mind, the basic design for a bedded pack area is given below.

Basic layout for a bedded pack area with water access only from the concrete feed alley

The bedded pack area should be rectangular with the longest side adjacent to the feedbunk, and divided lengthwise to create a 12- to 14-foot (3.7 to 4.3 m) wide concrete apron next to the bunk.  The area is typically no more than 30 to 35 feet deep (9.1 to 10.7 m). With flexibility in mind, the depth of the bedded area is equal to the width of two rows of freestalls and a stall alley, so it can be converted later if desired. The bedding must be contained so it does not drift onto the concrete apron by the use of a bedding retainer, the size and shape of which depends on the type of bedded pack being constructed.

A compost bedded barn showing the 4 feet (1.2 m) high bedding retainer and concrete apron adjacent to the feed bunk

Bedding Management

For traditional bedded packs with anaerobic fermentation, straw or similar organic bedding is added to the bedded area daily at a rate of approximately 25 lbs (11.3 kg) of bedding per cow per day. After a period of 4 to 6 weeks, the whole bed is removed and the process is repeated. A bedding retainer in this type of barn should be a 10 inch (25 cm) high, 8 inch (20 cm) wide concrete curb that is rounded at the edges. Such a retainer allows access to the bed along its length, thereby reducing the damage done to the bedded area by cow movement.

Compost barns are managed very differently than traditional bedded packs since they typically utilize dry fine wood sawdust or shavings as a bedding material. The fine particles are necessary to improve mixing and aeration. Straw, cornstalks, and green or wet shavings are not recommended. Initially, 12 to 18 inches (31 to 46 cm) of dry fine wood shavings are placed on the floor. Fresh bedding is added at intervals dependent on weather conditions, stocking rates, and cow hygiene scores. Most importantly, the bed is aerated at least twice daily. Producers utilize a cultivator mounted on a skid-steer or a tractor-mounted rototiller to stir the bed to a depth of 8 to 12 inches (20 to 31 cm). Cultivation incorporates manure and urine below the surface and aerates the pack, which speeds up microbial breakdown and composting. There is some debate as to whether the pack truly achieves temperatures of greater than 140 °F (60 °C). To date, available data suggests the average temperature is 108 °F (42 degrees °C), meaning the bedding material is only partially composted.

The bed may be removed once or twice per year (spring and fall or fall only), depending on the availability of land and the building design. To operate this type of bedded pack, the sidewalls must be solid and at least 4 feet high (1.2 m). Thus, bedded area access in this type of barn must be limited to at least two points, but traffic damage to the bedded area in these locations is a problem. In larger barns, access to the resting area needs to be located at 120- to 160-foot intervals (36.6 to 48.8 m). The loss of approximately 200 square feet (18.6 sq m) of bedded area adjacent to each opening must be considered when calculating bedded space per cow. To prevent cows from walking over the wall adjacent to the feed alley after the pack has built up over time, a fence is recommended along the top of the wall.

The compost in the barn pictured has recently been aerated. Note the high sidewalls and the distance between the trusses and the bedded area permitting equipment access and good cross ventilation.

The floor beneath the bedded area should allow drainage of moisture away from the surface. Many use concrete, but this must be sloped so that liquid does not collect in one corner of the bed. Others suggest a dirt or clay surface, but some local regulations preclude this. A drainage tile covered with pea gravel is an expensive option requiring annual maintenance, but these systems will use less bedding due to the lower moisture content, and are preferred for anaerobic packs.

Space Allowance

Bedded area space allowances for cows of various body sizes are estimated in the table below. Typical mature Holstein dairy cows require a minimum of 90 square feet (8.4 sq m) of bedded space per cow. Heavily pregnant cows in a close-up pen require at least 120 square feet (11.2 sq m) per cow. We recommend 150 square feet (13.9 sq m) per cow in maternity areas.

Minimum effective space allowance for bedded area for mature lactating dairy cows. This allowance does not include the concrete feed alley nor the areas of bedding which may be spoiled around entrance and exit points.

Ventilation

High sidewalls are necessary to facilitate natural ventilation (air exchange with the outside) in bedded pack barns. While traditional packs may need only a 14-foot (4.3 m) sidewall in cool climates and 16- to 18-foot (4.9 to 5.5 m) sidewall in hot climates, compost barns need a minimum of a 16-foot sidewall height to provide greater access for bedding trucks and bedding cultivating equipment because of the accumulation of bedding. Circulation fans spaced over the bedded area facilitate air movement and reduce moisture in compost bedding, but they must be hung high enough to avoid equipment. A 3- to 6-foot (0.9 to 1.8 cm) eave overhang is recommended to minimize the chance of roof runoff and rain being blown onto the bedded pack. If the pack is located below an open ridge outlet, the ridge opening must be modified to reduce the risk of water entry.

Information on this page is based off of materials from Dr. Marcia Endres from the University of Minnesota and Dr. Jeff Bewley of Cow Focused Solutions.