Seasonal and within-herd variability of E. coli concentrations in fresh dairy faeces

Abstract

The aim of this study was to determine concentrations of culturable faecal indicator organisms (FIOs) in freshly excreted dairy faeces and assess seasonal, within-herd and year-on-year variability in counts. Such values are essential in order to provide input parameters and associated uncertainty bounds for empirical models designed to determine the burden of FIOs on pasture. A longitudinal faecal analysis survey (n = 80) was conducted at a conventional dairy farm in central Scotland over a 2-year period. The analysis quantified counts of Escherichia coli and other nonE. coli coliforms and compared the concentrations of these FIO groups across contrasting seasons. The overall mean concentration of E. coli was 6.63 and 6.58 log10 CFU g(-1) dry weight in 2012 and 2013, respectively. However, concentrations of E. coli in faecal pats on each seasonal sampling event were highly variable and spanned several orders of magnitude on all occasions. Concentrations of E. coli in faeces excreted in winter were found to be lower than those excreted in all other seasons in 2012, though patterns of seasonal shedding were not consistent in observations the following year highlighting additional sources of uncertainty in FIO loading to land from dairy herds. This study provides a comprehensive temporal data set of faecal indicator organism (FIO) counts (both E. coli and other coliforms) in fresh dairy faeces for Scotland. Such faecal audits for the UK are scarce which is surprising given that livestock constitute one of the largest agricultural sources of diffuse microbial pollution of surface waters and contributors to poor bathing water quality. Such FIO concentration data (and evaluation of variability across seasonal, within-herd and year-on-year counts) in fresh faeces is a fundamental precursor to the robust parameterization of models that aim to predict the fate and transfer of both FIOs and pathogens in agricultural catchments.