The relationships between faecal worm egg count and subjectively assessed wool and conformation traits in the Tygerhoek Merino flock
Subjectively assessed wool and conformation traits form part of the selection objective in wool sheep enterprises. The present study investigated the genetic, phenotypic and environmental correlations for nematode resistance (using faecal worm egg count (FEC)) with subjectively assessed wool and conformation traits. The Merino sheep flock (consisting of four lines) maintained on Tygerhoek Research Farm was used. Fixed effects of selection line, birth type, sex, age of dam in years, year of birth, and sex*birth year interaction had a significant effect on all subjective traits. At genetic level, log transformed FEC was significantly related to wool oil only at 0.18 ± 0.09, staple formation at 0.29 ± 0.10, and topline at −0.33 ± 0.11. These correlations suggested that sheep with high FEC are likely to have excessive wool oil, thicker and bulkier staples, and lower scores for topline. Selection for resistance to and resilience against nematodes in Merino sheep thus will not result in marked unfavourable correlated responses in the vast majority of these subjective wool and body conformation traits.
Keywords: Linearly assessed traits, faecal worm egg count, conformation, correlations