Detection and quantification of species-specific gastrointestinal nematode DNA in goat feces using quantitative PCR

Goats are important livestock species in tropical and subtropical regions. However, they are susceptible to gastrointestinal nematode (GIN) infections, which can significantly reduce their productivity. Therefore, accurate diagnosis and effective control of GIN are essential for the management of goat production. In this study, we investigated the feasibility of detecting two GIN species in fecal samples using a DNA quantification method and quantifying the parasite load for each species. We identified two species, Haemonchus contortus and Trichostrongylus colubriformis, by direct DNA sequencing of a single egg. Subsequently, we measured the DNA copy number (DCN) of each nematode in the sample using absolute quantitative PCR and verified the relationship between the DCN and number of eggs per gram (EPG). Correlation analysis indicated a significant positive correlation between the total DCN and EPG (rho = 0.85, p < 0.001). Subsequently, linear regression analysis adequately explained the relationship between each DCN and the EPG (adjusted R-squared = 0.61, p < 0.001). There was no significant difference in the amount of DNA per egg between H. contortus and T. colubriformis (p = 0.7922). The estimated EPG from the DCN tended to be higher than the measured EPG (the mean relative error was 5.23 ± 13.74). This study showed that qPCR quantification of H. contortus and T. colubriformis DNA in goat feces reflects species-specific infection intensity and has the potential to complement conventional diagnostic and epidemiological approaches.