Abstract
Fecal egg count (FEC) is an indicative measurement for parasite infection in sheep. Different FEC methods may show inconsistent results. Not accounting for inconsistencies can be problematic when integrating measurements from different FEC methods for genetic evaluation. The objectives of this study were to: evaluate the difference between two FEC methods, the Modified McMaster (LMMR) and the Triple Chamber McMaster (LTCM); estimate the genetic and phenotypic correlations between records from two methods; and estimate genetic parameters for FEC and other gastrointestinal parasite resistance traits. A total of 1,676 fecal samples were collected from a commercial sheep farm between 2012 and 2019. Fecal egg counting was performed using the Modified McMaster (n = 998) and the Triple Chamber McMaster (n = 678) methods. Other parasite resistance trait records were collected from the same farm including eye score (FAMACHA©), body condition score (BCS), and body weight (WT). The mean and variance between the two FEC methods were significantly different (P < 0.0001), but phenotypic and genetic correlations between them were high (0.88 and 0.94, respectively). Therefore, pre-adjustment is required prior to integrating data from the different methods. For multiple trait analysis with other parasite resistance traits, data from the two fecal egg counting methods were integrated (LFEC) by using records for the LMMR when available and replacing missing records with standardized LTCM records for mean and variance of LMMR. Heritability estimates were 0.12, 0.07, 0.17, and 0.24, for LFEC, FAMACHA©, BCS, and the WT, respectively. Estimated genetic correlations between fecal egg count and the other parasite resistance traits were low with FAMACHA© (0.24), BCS (-0.03), and WT (0.22), suggesting little to no benefit of using such traits as indicators for LFEC.