Open-air windrows for winter disposal of frozen cattle mortalities: effects of ambient temperature and mortality layering

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After imposition of fees for disposal of cattle carcasses by the rendering industry, on-farm methods of mortality disposal are being investigated. Three open-air mortality compost windrows were constructed in January (JAN) and February (FEB) of 2004 in the cold, semiarid climate of southern Alberta, Canada. Windrow A included a base of barley straw a minimum of 46 cm thick, a layer of cattle mortalities (n=12) and a layer of stockpiled manure (minimum of 46 cm) covering the mortalities. Windrows B and C also had a bottom layer of barley straw, with windrow B containing 9 mortalities in 2 layers and windrow C containing 12 mortalities in 3 layers. Due to ambient temperatures < 0oC, carcasses (range 236 to 673 kg) were frozen at the time of windrow construction. Type 'T' thermocouples were embedded at the base of B and C windrows and temperatures within 120 cm of the surface were measured using a stainless steel dial probe.

Windrows were turned 3 times at 3 mo intervals. Samples were collected from initial compost amendments and prior to each turning for determination of dry matter (DM), organic matter (OM), N, C and coliform bacteria. Ambient temperature was 13oC higher (P < 0.05) for the initial heating of FEB as compared to JAN compost, although the rate of compost temperature decline did not differ between replicates in this period. Days at maximum temperature did not differ between replicates and maximum temperatures in all windrows exceeded 55oC. After 3 heating periods and 9 mo, flesh was not evident and only fragments of bones (max wt. 740 g) were found. Results of this study demonstrate that ambient temperatures < 0oC and frozen mortalities provide no barrier to the use of open-air windrows for disposal of cattle mortalities. As well, stacking up to 3 layers of full-sized cattle mortalities in a windrow did not affect temperature profiles, residual flesh or bone, or analyses of the finished compost. Under the climatic conditions of southern Alberta, layering mortalities would reduce space requirements for large-animal mortality composting in a feedlot setting.

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