The present study was aimed to evaluate the influence of flotation solution, sample
dilution, and the choice of McMaster slide area (volume) on the reliability of the
McMaster technique in estimating the faecal egg counts of gastrointestinal (GI) strongyles
and Dicrocoelium dendriticum in a composite sample of faeces from naturally infected
sheep. Fourteen flotation solutions having densities between 1.200 and 1.450, and
six sample dilutions, 1:10, 1:15, 1:20, 1:30, 1:40 and 1:50 were used. Each of the
six dilutions was divided into 70 aliquots in order to have five replicates of each
of the 14 flotation solutions at each of the six dilutions. For each McMaster slide,
the GI strongyle and D. dendriticum egg counts were performed under one grid (McM
0.15 ml), two grids (McM 0.3 ml), one chamber (McM 0.5 ml), and both chambers (McM
1.0 ml). Mean eggs per gram (EPG) of faeces of GI strongyles and D. dendriticum were
calculated and statistical analyses were performed on the resulting data. The type
of flotation solution used significantly influenced the EPG in the GI strongyles and
in the D. dendriticum egg counts. All the sucrose-based solutions at density between
1.200 and 1.350 floated more GI strongyle eggs than the others. With respect to D.
dendriticum, only six solutions were capable of floating eggs and the potassium iodomercurate
solution (density 1.440) floated more eggs than the others. The reliability of the
McMaster technique regarding sample dilution was high for both GI strongyle and D.
dendriticum EPG at 1:10 and 1:15, and then progressively decreased with increasing
dilution. The reliability of the McMaster technique regarding the choice of the McMaster
slide area (volume) was high for both GI strongyle and D. dendriticum EPG at the McMaster
slide area (volume) of 1.0 ml, i.e. the total area of the McMaster slide. The EPG
counts resulting from choosing any of the other three McMaster slide areas (volumes),
i.e. McM 0.15 ml, McM 0.3 ml, or McM 0.5 ml, produced unreliable over-estimates. The
findings of the present study show that the highest reliability of the McMaster technique
for estimating GI strongyle and D. dendriticum egg counts in faeces from pastured
sheep is obtained when using flotation solutions based on sucrose for GI strongyles,
and potassium iodomercurate for D. dendriticum, dilutions which do not exceed 1:15,
and the McMaster slide area (volume) of 1.0 ml.