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Phenotypic markers for selection of nematode-resistant sheep
P G Douch1, R S Green, C A Morris
1AgResearch, Wallaceville Animal Research Centre, Upper Hutt, New Zealand. douchp@agresearch.cri.nz
International Journal for Parasitology
|August 1, 1996
Summary
Nematode resistance in sheep can be improved by identifying immunological markers, such as antibody levels, to select for animals with better natural defenses against parasitic worms. This approach offers a more practical alternative to traditional fecal egg counts for breeding programs.
Area of Science:
- Animal Science
- Immunology
- Parasitology
Background:
- Nematode resistance in sheep is crucial for animal health and productivity.
- Traditional measurement via fecal egg counts (FEC) has limitations, including production penalties and artificial challenge needs.
- Heritability of nematode resistance is approximately 0.3 in Romney and Merino sheep.
Purpose of the Study:
- To explore immunological parameters as potential phenotypic markers for nematode resistance in sheep.
- To identify easily measurable, cost-effective, and automatable markers correlated with genetic resistance.
- To overcome the practical limitations of using FEC for selection.
Main Methods:
- Investigated antibody levels (IgG1) against excretory/secretory antigens of L3 nematodes (e.g., Trichostrongylus colubriformis).
- Assessed blood eosinophil counts as a potential selection parameter.
- Considered other immunological markers like serum nematode-specific IgE and mast cell products.
Main Results:
- Antibody levels (IgG1) to L3 nematode antigens show promise as phenotypic markers for nematode resistance.
- These antibody levels are independent of on-farm drenching strategies.
- Blood eosinophil counts exhibit high variability, limiting their potential as selection markers.
Conclusions:
- Immunological parameters, particularly antibody levels to nematode antigens, can serve as effective phenotypic markers for sheep nematode resistance.
- Further research into sheep immune responses may reveal new immunological and genetic markers.
- Defining critical immune responses will aid in identifying and characterizing genetic markers for improved breeding strategies.