Viability of Rhodococcus equi and Parascaris equorum eggs exposed to high temperatures.

There is great concern about the potential pathogen contamination of horse manure compost spread in the same fields horses graze in. To ensure that pathogen destruction occurs, temperatures need to be sufficiently high during composting. Here, we investigated the survival rate of two marker organisms, Rhodococcus equi and Parascaris equorum eggs, exposed to temperatures potentially encountered during horse manure composting. Our results show that the time required to achieve a 1 log10 reduction in R. equi population (D-value) are 17.1 h (+/-1.47) at 45 degrees C, 8.6 h (+/-0.28) at 50 degrees C, 2.9 h (+/-0.04) at 55 degrees C and 0.7 h (+/-0.04) at 60 degrees C. For P. equorum eggs we show that at 45 and 50 degrees C, 2 log10 reduction of viability is reached between 8 and 24 h of incubation and that it takes less than 2 h at 55 and 60 degrees C to achieve a viability reduction of 2 log10. These results are useful for identifying composting conditions that will reduce the risk of environmental contamination by R. equi and P. equorum eggs.