Across flock (co)variance components fpr faecal worm egg count, live weight, and fleece traits for Australian merinos

A field data set was used to estimate heritability of resistance to gastrointestinal nematode parasites and phenotypic and genetic correlations between resistance and production traits in Australian merinos. Faecal egg count (FEC) was measured at two different ages, namely, around 1 year on 16,669 animals out of 650 sires and on 5110 animals from 157 sires at hogget age (16 months). Wool production and live weight data were known for the animals at both yearling and hogget ages. An animal model was used to estimate variance components accounting for birth type, dam age, age of animal, and contemporary group. Maternal effects were small but significant (P≤0.05) for yearling faecal egg count (YFEC), yearling greasy fleece weight (YGFW), yearling clean fleece weight (YCFW), hogget greasy fleece weight (HGFW), and hogget clean fleece weight (HCFW), and nonsignificant for hogget faecal egg count (HFEC) and other production traits. Heritability (±S.E.) of YFEC was 0.21±0.02 and, for HFEC, it was 0.38±0.03. Genetic and phenotypic correlations between YFEC and HFEC were 0.27±0.13 and 0.37±0.04, respectively. Genetic correlations of FEC with CFW, GFW, fibre diameter, and body weight were 0.11±0.08, 0.07±0.07, −0.05±0.07, and −0.14±0.07 at yearling age and −0.01±0.08, 0.07±0.04, −0.05±0.02, and −0.10±0.07 at hogget age.