title: Breeding for resistance to gastrointestinal nematodes - the potential in low-input/output small ruminant production systems.
abstract: The control of gastrointestinal nematodes (GIN) is mainly based on the use of drugs, grazing management, use of copper oxide wire particles and bioactive forages. Resistance to anthelmintic drugs in small ruminants is documented worldwide. Host genetic resistance to parasites, has been increasingly used as a complementary control strategy, along with the conventional intervention methods mentioned above. Genetic diversity in resistance to GIN has been well studied in experimental and commercial flocks in temperate climates and more developed economies. However, there are very few report outputs from the more extensive low-input/output smallholder systems in developing and emerging countries. Furthermore, results on quantitative trait loci (QTL) associated with nematode resistance from various studies have not always been consistent, mainly due to the different nematodes studied, different host breeds, ages, climates, natural infections versus artificial challenges, infection level at sampling periods, among others. The increasing use of genetic markers (Single Nucleotide Polymorphisms, SNPs) in GWAS or the use of whole genome sequence data and a plethora of analytic methods offer the potential to identify loci or regions associated nematode resistance. Genomic selection as a genome-wide level method overcomes the need to identify candidate genes. Benefits in genomic selection are now being realised in dairy cattle and sheep under commercial settings in the more advanced countries. However, despite the commercial benefits of using these tools, there are practical problems associated with incorporating the use of marker-assisted selection or genomic selection in low-input/output smallholder farming systems breeding schemes. Unlike anthelmintic resistance, there is no empirical evidence suggesting that nematodes will evolve rapidly in response to resistant hosts. The strategy of nematode control has evolved to a more practical manipulation of host-parasite equilibrium in grazing systems by implementation of various strategies, in which improvement of genetic resistance of small ruminant should be included. Therefore, selection for resistant hosts can be considered as one of the sustainable control strategy, although it will be most effective when used to complement other control strategies such as grazing management and improving efficiency of anthelmintics currently.
authors.affiliation: Department of Animal Sciences, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa; Department of Para-clinical Veterinary Studies, University of Zimbabwe, P.O. MP167, Mt. Pleasant, Harare, Zimbabwe. Electronic address: ivy.zvinorova@gmail.com.
authors.forename: P I
authors.initials: PI
authors.lastname: Zvinorova
authors.affiliation: Department of Animal Science, University of Zimbabwe, P.O. MP167, Mt. Pleasant, Harare, Zimbabwe. Electronic address: tinyiko@agric.uz.ac.zw.
authors.forename: T E
authors.initials: TE
authors.lastname: Halimani
authors.affiliation: Biotechnology Platform, Agriculture Research Council Private Bag X5, Onderstepoort, 0110, South Africa. Electronic address: MuchadeyiF@arc.agric.za.
authors.forename: F C
authors.initials: FC
authors.lastname: Muchadeyi
authors.affiliation: The Roslin Institute and R(D)SVS, University of Edinburgh, Easter Bush, MidlothianEH25 9RG, UK. Electronic address: oswald.matika@roslin.ed.ac.uk.
authors.forename: O
authors.initials: O
authors.lastname: Matika
authors.affiliation: The Roslin Institute and R(D)SVS, University of Edinburgh, Easter Bush, MidlothianEH25 9RG, UK. Electronic address: valentina.riggio@roslin.ed.ac.uk.
authors.forename: V
authors.initials: V
authors.lastname: Riggio
authors.affiliation: Department of Animal Sciences, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa. Electronic address: kdzama@sun.ac.za.
authors.forename: K
authors.initials: K
authors.lastname: Dzama
mesh_terms: D000818:Animals; D001947:Breeding; D014644:Genetic Variation; D006790:Host-Parasite Interactions / Q000235:genetics*; D009348:Nematoda; D009349:Nematode Infections / Q000235:genetics / Q000517:prevention & control / Q000662:veterinary*; D012418:Ruminants / Q000469:parasitology*
keywords: Faecal egg counts; Nematode resistance; SNPs; Selection; Small ruminants