Fate of pathogens present in livestock wastes spread onto fescue plots

Abstract

Fecal wastes from a variety of farmed livestock were inoculated with livestock isolates of Escherichia coli O157, Listeria monocytogenes, Salmonella, Campylobacter jejuni, and Cryptosporidium parvum oocysts at levels representative of the levels found in naturally contaminated wastes. The wastes were subsequently spread onto a grass pasture, and the decline of each of the zoonotic agents was monitored over time. There were no significant differences among the decimal reduction times for the bacterial pathogens. The mean bacterial decimal reduction time was 1.94 days. A range of times between 8 and 31 days for a 1-log reduction in C. parvum levels was obtained, demonstrating that the protozoans were significantly more hardy than the bacteria. Oocyst recovery was more efficient from wastes with lower dry matter contents. The levels of most of the zoonotic agents had declined to below detectable levels by 64 days. However, for some waste types, 128 days was required for the complete decline of L. monocytogenes levels. We were unable to find significant differences between the rates of pathogen decline in liquid (slurry) and solid (farmyard manure) wastes, although concerns have been raised that increased slurry generation as a consequence of more intensive farming practices could lead to increased survival of zoonotic agents in the environment.

FIG. 1.

Loss of ammonium N from experimental plots over time. The data are averages derived from a range of fresh manure types as described in Materials and Methods and are the percentages of ammonium N remaining, as calculated from the amount applied initially. The error bars indicate the standard deviations of the means obtained from 27 experimental plots.

FIG. 2.

Decline of Salmonella (•), Listeria (▿), Campylobacter (▾), and E. coli O157 (O) in cattle wastes. Solid wastes (A and C) and liquid wastes (B and D) were obtained from beef cattle (A and B) and dairy cattle (C and D).

FIG. 3.

Environmental decline of C. parvum spread onto grass. Oocysts were inoculated into livestock wastes (pig slurry [A] and pig FYM [B]), which were subsequently spread onto grass pasture planted in a clay-loam soil. The bars and the y axis on the left indicate the mean levels of oocysts recovered from each sample. The error bars indicate the standard deviations of the means obtained from three independently analyzed experimental plots. The solid triangles and the y axis on the right show the mean viability of the oocysts isolated from each plot on which waste was spread.

FIG. 4.

Rainfall (bars) and temperature (line) for grass pasture plots spread with animal wastes inoculated with zoonotic agents, including C. parvum. The wastes were spread in late spring, and temperature and rainfall were monitored for 12 weeks after spreading. The gaps in the temperature profile were generated on the days that the temperature recorder was taken indoors for downloading.