Slurry Management and Minimising Slurry Pooling

Slurry and muck are excellent mediums for supporting many bacterial and viral species, including a number of pathogens responsible directly or indirectly for lameness problems like digital dermatitis. Infections can enter through injuries or damage to hooves, and dirty, wet conditions can soften hoof horn to increase the potential of stones or other foreign bodies causing problems.

In cubicle-housed systems the frequency of passageway scraping can make a great difference to the cleanliness of the cows and can offer important benefits in terms of reducing the potential for cows to slip, fall or be pushed by other cows - causing injuries and teat/udder contamination - and reducing overall lameness problems. Collecting yards should be scraped before or after every milking and loafing areas should be kept clean. Passageways should be scraped at least twice per day. These areas where cows collect and travel through must drain well to stop slurry pooling and have good grip surfaces.

Automatic scraping systems can improve cleanliness levels but practical experience has shown that scraped runs should be kept below a maximum of 25 metres to avoid the effect of a bow wave of slurry building-up in front of the scraper blade - the increased soiling of the foot and lower leg associated with automatic scrapers can contribute to the spread of slurry-borne diseases like digital dermatitis - irrespective of how frequent the scraping cycle is set to run, although scraping frequency itself does obviously play a role in cleanliness. Where long runs of over 25 metres cannot be avoided, the installation of slatted cross passageways along the length of the scraper run can be considered.

Flood washing or flushing, using water to flood the cubicle passageways to remove slurry, is a system that has been proven to keep cubicle passageways particularly clean. However, the system relies upon a partial recycling of the water used which means that there is a potential for contaminants to be collected and re-distributed with each washing with increasing potential risk to cow health. The replacement of around 20% of the stored flushing water with fresh supplies goes some way to reducing this problem but it can mean that the system's suitability is limited by the cost and availability of water.

Effective flood washing also relies on a suitable passageway slope of 2-4%, enabling the creation of a wave of water of around 20m in length and 75mm in depth moving at a speed of 2m/sec, so that a good result is achieved with the minimum of water. The process is repeated 3 times per day and in order to maintain the momentum of water and to avoid contamination of feet, legs, teats and udders, cows should not be present during the washing process.

Slatted floor housing systems also offer improvements in cleanliness, but often in slatted systems a build-up of slurry and muck is observed in solid-floored areas like cross passages, and around water troughs and at the back of cubicles, which tends not be removed or scraped as often as non-slatted systems. It is important that areas where slurry can pool in any system are routinely scraped to avoid a build-up of muck and the infections which can thrive in slurry.

Slat type and shape play an important role in cow comfort and effectiveness of slurry removal; slats must have solid, smooth edges and the width of slat and therefore the size of the gap between slats must provide adequate support for the cow's foot while at the same time ensuring that slurry and muck can fall easily through. Recommendations for slats for dairy cows are for a slat width of 140-160mm and spacing between slats of 35-40mm. Rubberised coverings are available to further improve cow comfort on slatted floors.

Hygiene scoring can be used as a means of measuring the overall effectiveness in the housing and grazing system of keeping cows clean and can indicate problem areas in muck and slurry handling systems.

The material chosen for bedding can itself pose problems for muck and slurry disposal. Large amounts of straw, particularly if not short-chopped, can cause problems by blocking slats and pumps. Sand, while providing the ideal bedding material in terms of cow comfort and welfare, provides particular problems in wearing slurry scrapers, passageways, slurry pumps and other machinery and equipment used to handle and dispose of it at a much quicker rate and this has to be considered when costing and planning a sand-based system.