Health risks associated with the mechanical laying of straw bedding in cattle sheds

The Health and Safety Laboratory (HSL) has recently conducted a brief survey to measure and assess the health risks associated with the mechanical laying down of straw bedding in cattle houses. A small number of farms were visited when bedding was being laid down using various types of mechanical spreaders powered by a tractor or similar farm vehicle.

The frequency that fresh straw is added to cow sheds varies from farm to farm and also, on some farms, on the season. Cows are housed in sheds for a much higher proportion of time during the winter months.

It was found that the tractor driver and any other workers in the vicinity of the cattle shed may inhale straw dust and its associated contaminants not only during but also after the task has been completed unless entry is prohibited until the air inside the building has had time to clear.

Straw (chopped or whole) and similar by-products of field crops such as stems of oilseed rape will naturally carry a population of fungi and other micro-organisms, although the types and numbers will depend on the conditions during harvesting and storage. When the material is handled these contaminants and some of their breakdown products may become airborne and present an inhalation risk.

The principal agents of concern identified in this work were endotoxins, various fungal species (including Aspergillus fumigatus), bacteria and actinomycetes. These are known to cause respiratory disease in various forms, including acute conditions such as toxic organic dust syndrome. Long term or repeated exposure to high concentrations of fungal spores is known to cause respiratory diseases including ‘Farmer’s Lung’ (Reboux et al, 2001). Measurement of total inhalable particulate, and the use of an exposure limit based on this, is therefore inappropriate as an indicator of risk in this situation.

The driver of the tractor towing the straw laying equipment is at the highest risk of exposure. In principal, the use of air filtration on the tractor cab offers the potential to adequately control the driver’s exposure. In practice, inappropriate use and inadequate maintenance compromised the efficacy of cab air filtration and bad practice was evident at some of the sites visited during the survey. If cab air filtration is available it needs to be correctly maintained and used properly. Cab windows should not be open during straw chopping and laying. If cab air filtration is not possible, then RPE must be worn by the tractor driver.

Access to areas affected by airborne dust should be restricted during straw laying. If entry to affected areas by others during straw chopping and laying is unavoidable, the use of appropriate RPE is necessary. Otherwise workers should not enter the shed until the air inside has had adequate time to clear.