Genetic parameters of animal traits associated with coccidian and nematode parasite load and growth in Scottish Blackface sheep

AFP Pacheco, Tom N McNeilly, Georgios Banos, JE Conington*

*Corresponding author for this work

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Abstract

Gastrointestinal parasitism is a global problem for grazing ruminants which can be addressed in a sustainable way through breeding animals to be more resistant to disease. This study estimates the genetic parameters of common and new disease phenotypes associated with natural nematode and coccidian infection in Scottish Blackface sheep to underpin future genetic improvement strategies for parasite control. Data on faecal egg counts (FEC) from different species of strongyle parasites and faecal oocyst counts (FOC) from coccidian parasites were collected on three-month old lambs together with a faecal soiling score in the breech area (DAG) and live body weight (LWT). Faecal count data were obtained for Strongyles (FECS), Nematodirus (FECN) and Coccidia (FOC). Data from 3,731 lambs sampled between 2011 and 2017 were included. FEC and DAG records were log-transformed prior to analysis. Data were analysed using linear mixed models. Average age at sampling was 92 days with a mean LWT of 24.5 kg. Faecal soiling was not evident in 69% of lambs. Coccidia were the most prevalent parasite (99.5%), while Strongyles and Nematodirus had prevalence of 95.4% and 72.7%, respectively. Heritability estimates (± standard error) were 0.16 ± 0.03, 0.17 ± 0.03, 0.09 ± 0.03, 0.09 ± 0.03 and 0.33 ± 0.04 for FECS, FECN, FOC, DAG and LWT, respectively. FECS had a strong and positive genetic correlation with FECN (0.74 ± 0.09) and a moderate positive correlation with FOC (0.39 ± 0.15) while DAG was negatively genetically correlated with LWT (-0.33 ± 0.15). The significant positive genetic correlations between FECS, FECN and FOC at three months of age show that co-selection of sheep for resistance to these different parasites is feasible. Selection for increased resistance to parasite infection is not expected to adversely affect live body weight, as no significant antagonistic genetic correlations were found between LWT and faecal egg counts. There were significant antagonistic phenotypic and genetic relationships between DAG and LWT being -0.19 ± 0.02 and -0.33 ± 0.15, respectively, indicating that the expression of the manifestation of disease in lambs may be a more meaningful indicator of the impact of parasite burden on productivity.
Original languageEnglish
Article number100185
JournalAnimal
Volume15
Issue number4
Early online date27 Feb 2021
DOIs
Publication statusPrint publication - Apr 2021

Keywords

  • Gastrointestinal parasites
  • Genetic resistance
  • Heritability
  • Selection
  • Sheep

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