Design Considerations for Compost Bedded-packs

An in-depth literature review of the existing industry best practice has been performed by Dr Phil Chamberlain on behalf of Subtropical Dairy and is summarised here.

Download the full literature review

Recommended bedded pack variables

Variable Recommendation Practical Assessment of Variable 
Temp (C)

Surface Bed: Ambient

Deep Bedding: 45 - 65

The pack temperature is used as a guide to the level of microbial activity and the speed of organic matter breakdown and is ideally kept between 45°C to 66°C  below the surface, and surface temperatures generally remains close to ambient.

If the pack temperature is lower than 40°C, the composting process is too slow, and pack temperatures above 66°C will result in bacterial death. Both situations result in the pack becoming inactive and then then too wet from urine and faeces not being broken down.
Moisture (%)

Surface Bed: 15%

Deep Bedding: 50-60

The moisture content is easily estimated by squeezing a handful of bedding in the hand. If water can be squeezed out, the pack is too wet, but if you can't form a ball that stays in shape the pack is too dry.

Upper layer moisture content of <15% is required to maintain cow cleanliness, low cell counts and cow health. To maintain this environment, additional bedding is required, ranging from 4.5kg - 15.9kg (up to 18) kg/cow per day.
pH 6.5-8.0 Lower pHs can be maintained with good pack management.
 Ratio (C:N)   25:1 – 30:1

 If you can smell ammonia, the C/N ratio is likely below 25:1

 

Mastitis-causing bacteria in compost bedding

 Cause Observations 

Coliforms

CBP temperature, CBP moisture, space per cow and C/N ration had no effect on coliform counts

Escherichia

reached a peak concentration when the C/N ratio was between 30:1 and

35:1 (ideal C/N ratio is between 25:1 to 30:1)

Staphylococcus

counts increased mainly as ambient temperature increased.

 Streptococci

counts decreased with decreased stocking rate and increased composite temperature and increased with increasing ambient temperature and moisture.

peaked at aC/N ratio ranging from 16:1 to 18:1. 

 Bacillus

 counts were reduced with increasing moisture, C/N ratio, and ambient temperature.

Other ambient temperature considerations;

  • Researchers have also discovered that Barn Temperature (BT) has an important influence on bacterial growth in CPB and that CPB may be more difficult to manage in warmer environments.
  • These indicate that a higher BT has a positive effect on composting activity and cow hygiene scores, however has a negative effect on SCC and coliform growth and will also increase heat stress on cows.

 

Bed Materials Selection

Some materials will be more suitable than others, but in some instances, a combinations of materials have been trialled with varying success. 

Suitable materials

Materials  Reasoning
Kiln-dried Sawdust Performs well as long as the moisture content is less than 18% on entry
Chopped Straw Ensure straw is chopped very short, absorbent and non-waxy. Ideal straw length is < 2cm.
Straw  Low surface to volume area, may not be appropriate for compost beds.
 Recycled Manure Solid  Unsuitable in moister environments, maybe successful in drier conditions.
 Soil Might not provide enough carbon or moisture absorbing capacity and could potentially be too moist. 
 Chipped Wood  Less effective than sawdust and shavings due to low surface area/volume ratio; sharp and cause injury.
 Wood Shavings  Mixed with sawdust to improve tillability and aeration. Supports microbial breakdown of manure and urine and prevents excessive compaction.

 

Unsuitable materials 

Materials Reasoning
Course hay  Uneven tillage and patchy pack performance
Cereal grain straw  Clumps during cultivation, decreasing the effectiveness as bedding material.
 Oily and fragrant woods like cedar, black walnut, and cherry  Antimicrobial properties that interfere with the composting process. 
 Green Sawdust  May contain Klebsiella bacteria (mastitis pathogen), too wet.
Long corn stalk, waste hay, as well as oaten, barley, and wheat straw  Less absorption & dries slowly. 

The cost of bedding and availability of bedding materials were the major concerns expressed by the producers.

 

Design and construction

Site selection and preparation

  • Barns or feedpads with compost packs require excellent ventilation.
  • Work with prevailing winds to dry out the compost pack.
  • If an internal concrete alleyway is constructed, then approximately 25 to 30% of manure and urine is collected. A handling facility for slurry manure, such as a lagoon, must be constructed. Otherwise, daily manure hauling is needed.

Orientation and sunlight

An East and West orientation is preferred. This prevents the sun from drying the compost and encourages the cows to congregate into shaded areas. Avoid compacting and excess moisture in the shaded areas and over-drying in the pack areas that get more sun.

Structure

  • Roof supports need to be 4 to 5m in height of 3m open wall space (3) around all sides, starting at cow resting height.
  • Sidewall open area target is 0.093m2/cow in roof pitch of barns of less than 4:12 will limit the natural ventilation rate per cow.
  • Continuous ridge vent opening of at least 7.6 cm for every 3.0 m of roof width, with a minimum opening width of 30.5 cm.

Bedding pack area and stocking density

  • The recommended bedding area requirements can be 7 to 30 m2/cow (27).
  • High-producing herds will require more space because they will produce more urine & faeces. Minimum 1 m2 for each 11kg/day of increased milk production above 22kg/day.
  • Cows producing more than 40 litres/day require an area of more than 14 m2/cow for efficient composting to occur.

Sidewall curtains

Curtains should be fully raised in the summer to increase air flow and care should be taken in winter, to ensure that any restriction of air flow is not sufficient to create condensation, ammonia build up and a humid environment.

Additional ventilation and cooling

Without circulation fans in the barn, cows may tend to congregate in areas where natural air flow is higher, especially during heat stress conditions. Congregation of animals in one area leads to excessive manure and urine accumulation and ineffective composting from too high moisture in that pack region.

Consider installing box fans or high-volume low-speed fans that ca provide n appropriate ventilation can drastically reduce bedding costs ventilation, and that fan speeds of 9.6 km/h may increase the length of time bedding will last in a barn.

For more information on Compost pack facilities, visit the Dairy Infrastructure Website.