The comparison between Mini-FLOTAC and McMaster for GIN FEC in cattle showed that Mini-FLOTAC had a higher sensitivity and accuracy and a lower CV than the McMaster technique (grids and chambers). Interestingly, McMaster grids showed higher FECs than McMaster chambers for all levels of contamination (10, 50, 100, 200 and 500 EPG). As described in Cringoli et al. [18] and Bosco et al. [12] it may be due to the tendency of eggs, during the flotation, to concentrate in the center of the McMaster slide, with a consequent overestimation of EPGs, especially at low egg counts. Moreover, McMaster showed no statistically significant difference between observed and true EPG only at 500 EPG and at grids level of reading. These results, therefore, showed that the McMaster is not a satisfactory method at low EPG levels, especially when the FECRT is used to evaluate the efficacy of anthelmintics and to detect anthelmintic resistance [7, 12, 19].
In this study, the mean percentage of recovery of GIN eggs with Mini-FLOTAC was very high, i.e. 98.1%. This result is in agreement with Godber et al. [10] and Bosco et al. [12] who found a recovery rate of GIN eggs of 100% in sheep spiked faeces. The study by Paras et al. [7] showed a 70.9% recovery rate of cattle GIN eggs by Mini-FLOTAC that was higher than the values by other techniques (30.9% by modified Wisconsin and 55.0% by McMaster), but lower than the value detected in our study (98.1%). Similarly, Noel et al. [20] found a 42.6% recovery rate of equine strongyle eggs by Mini-FLOTAC, that was higher that the value from McMaster technique (23.5%). In the study on equine faecal samples by Napravnikova et al. [21] the accuracy of Mini-FLOTAC was 74.2% (lower than McMaster) for strongyles and 90.3% (higher than McMaster) for ascarids. Finally, Scare et al. [22] compared an automated FEC using a smartphone with Mini-FLOTAC and McMaster and found a higher accuracy by Mini-FLOTAC (64.5%) compared to McMaster (21.7%) and the smartphone system (32.5%).
As yet described in Cringoli et al. [8] and in Norris et al. [23], the procedure of egg isolation and faeces contamination, as well as the choice of the flotation solution may influence the recovery rates of a technique in any egg-spiking experiment. These factors may have contributed to the high recovery rate of GIN eggs in cattle using Mini-FLOTAC in our study as argued below. First, as regard the spiking procedure, in our study we spiked cattle faeces with GIN eggs obtained from cattle experimentally (in Belgium) or naturally (in Italy) infected by GINs. This could explain the higher accuracy compared to the findings by Paras et al. [7] where eggs isolated from goat faeces were used to contaminate cattle faeces. In support of our hypothesis, a recovery rate only of 91.0% was obtained by Bosco et al. [12] when GIN eggs from sheep were added to horse faeces. Second, the choice of the flotation solution is very important, because it might influence the performance of the technique and therefore its precision and accuracy [8].
In different studies it has been shown that sodium chloride (specific gravity = 1.200) was the best flotation solution for GIN FEC and it is recommended when using Mini-FLOTAC [8]. Therefore, the low recovery rates found in the above mentioned studies could be due to the inappropriateness of the flotation solutions (i.e. sodium nitrate with a specific gravity = 1.25–1.30 [7]; glucose-NaCl flotation medium with a specific gravity = 1.24–1.28 [20–22].
In our study, CVs of Mini-FLOTAC were lower than the CVs of McMaster grids and chambers for all levels of contamination as reported also in other studies [7, 10, 12, 13, 20–22, 24]. Furthermore, CVs for McMaster chambers were lower than those obtained with McMaster grids, in agreement with Godber et al. [10] and Bosco et al. [12]. To support these findings, Levecke et al. [25] and Torgerson et al. [26] showed that precision increases when analytical sensitivity increases; with the McMaster technique, the variance of EPG estimates between repeated samples of the same faecal sample is inflated, due to the multiplication factor when transforming the raw counts in EPG [26]. Moreover, in this study for all the techniques CVs were lower at higher levels of contaminations, in fact as reported also in Mes et al. [27] and in Das et al. [28] the precision increases when the EPG in faecal sample increases.
Since the sensitivity, precision and accuracy of a FEC depend by many factors, it’s very important to establish precise standard operating procedures (SOPs) for FEC techniques, including the flotation solution to use. In fact, it’s surprising that diagnostic and research laboratories around the world use different protocols of FEC techniques for their activities. In this view, research priorities should include the development of more scalable, reliable, less labour intensive systems for parasite egg counts for both pen-side and laboratory use [5] including methods of automated sample processing and image analysis [29] as indicated in the STAR-IDAZ (https://www.star-idaz.net) diagnostic road map for research on helminths and anthelmintic resistance.