Genetic variation in and relationships among faecal worm eggs recorded in different seasons of the year at the Tygerhoek farm in South Africa

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dc.contributor.authorMpetile, Ziyandaen_ZA
dc.contributor.authorDzama, Kennedyen_ZA
dc.contributor.authorCloete, Schalk W. P.en_ZA
dc.date.accessioned2019-02-18T10:04:01Z
dc.date.available2019-02-18T10:04:01Z
dc.date.issued2017-07-07
dc.descriptionCITATION: Mpetile, Z., Dzama, K. & Cloete, S. W. P. 2017. Genetic variation in and relationships among faecal worm eggs recorded in different seasons of the year at the Tygerhoek farm in South Africa. Journal of the South African Veterinary Association, 88:a1484, doi:10.4102/jsava.v88i0.1484.
dc.descriptionThe original publication is available at https://jsava.co.za/index.php/jsava
dc.description.abstractENGLISH ABSTRACT: Gastrointestinal nematodes result in severe economic and production losses to the sheep industry. An increase in resistance of the nematodes to chemicals used for control, as well as a demand of consumers for meat products free from chemicals, has fostered research on alternative control strategies. Breeding for resistance to nematodes offers an alternative to control parasitism but its effectiveness depends on genetic variation in faecal worm egg count (FWEC), an indirect measure of parasite resistance. A historic dataset of FWEC from four Merino lines subjected to natural parasite challenge was used to estimate genetic parameters for FWEC in three seasons (autumn, winter and spring) using a repeated records animal model, followed by a three-trait animal model analysis treating FWEC in different seasons as separate traits. The effects of selection line, birth year, sex, the sex x birth year interaction, season and the season x year interaction were significant when using 4994 records recorded from 1997 to 2000 (p < 0.001). The heritability of log-transformed FWEC amounted to 0.09 ± 0.02, with no contribution from the animal permanent environmental variance to the between animal variation across seasons. Three-trait heritability estimates for log-transformed FWEC amounted to 0.07 ± 0.05 in autumn, 0.13 ± 0.05 in winter and 0.19 ± 0.05 in spring. These results suggest sufficient genetic variation in FWEC to support selection for lower log-transformed FWEC. However, the best time to record data for selection is after the break of the season in winter and in spring, when sheep are stimulated by a greater intake of infective larvae from the pasture after the first rains. Genetic correlations among FWEC in the respective seasons were moderate to high, ranging from 0.55 to 0.89. Phenotypic correlations, on the other hand, were significant but lower in magnitude, ranging from 0.09 to 0.16. These results provide useful information for developing strategies for the genetic improvement of ovine resistance to gastrointestinal nematodes under Mediterranean conditions in South Africa by using FWEC as an indicator trait.en_ZA
dc.description.versionPublisher's version
dc.format.extent7 pagesen_ZA
dc.identifier.citationMpetile, Z., Dzama, K. & Cloete, S. W. P. 2017. Genetic variation in and relationships among faecal worm eggs recorded in different seasons of the year at the Tygerhoek farm in South Africa. Journal of the South African Veterinary Association, 88:a1484, doi:10.4102/jsava.v88i0.1484
dc.identifier.issn2224-9435 (online)
dc.identifier.issn1019-9128 (print)
dc.identifier.otherdoi:10.4102/jsava.v88i0.1484
dc.identifier.urihttp://hdl.handle.net/10019.1/105427
dc.language.isoen_ZAen_ZA
dc.publisherAOSIS Publishingen_ZA
dc.rights.holderAuthors retain copyrighten_ZA
dc.subjectGastrointestinal nematodes -- Controlen_ZA
dc.subjectSheep -- Breeding -- Geneticsen_ZA
dc.subjectSheep -- Parasitesen_ZA
dc.subjectFeces -- Analysisen_ZA
dc.subjectHelminths -- Controlen_ZA
dc.subjectNemotodes -- Controlen_ZA
dc.subjectParasite antigensen_ZA
dc.titleGenetic variation in and relationships among faecal worm eggs recorded in different seasons of the year at the Tygerhoek farm in South Africaen_ZA
dc.typeArticleen_ZA
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