title: Selection methods for resistance to and tolerance of helminths in livestock.
abstract: Helminthiases are among the most important livestock diseases worldwide, in particular for small ruminants, which are the focus of this review. Resource Allocation Theory implies that high-productivity farm animals proportionate insufficient resources for adequate coping with stressful conditions. Significant differences between breeds and within breeds are seen, as well as genotype vs. environment interactions. With improvement of genetic host resistance to infection, transmission of infection will be impacted. On the other hand, genetic improvement of resilience can lead to a reduction in clinical signs of disease, but not necessarily reduce transmission of infection to other animals. Faecal egg count (FEC) is the main measurement used to evaluate helminthiasis load, despite the fact that the protocols and analytical methods can affect the results, and the FEC data frequently shows aggregative, negative skewed distribution, and a high coefficient of variation. Mass selection where heritability is generally medium to low generally produces slow results and low economic returns. Many studies have been published linking resistance to nematodes in livestock to Quantitative Trait Loci and most studies have concentrated on chromosomes where the major histocompatibility complex region is located. Nevertheless, these complex traits have been seen to be affected by thousands of variants that each has a small effect. More recent studies have shown that genome-wide selection strategies can be useful in selecting animals for improved production and resistance traits in this case.
authors.affiliation: Vice-Coordinator INCT-Pecuaria, Universidade Federal do Rio Grande do Sul, Departamento de Zootecnia, Av. Bento Gonçalves, CEP 91540-000 Porto Alegre, Rio Grande do Sul, Brazil - Universidade de Brasília, Campus Darcy Ribeiro, 70910-900 Asa Norte, Brasilia, Distrito Federal, Brazil.
authors.forename: Concepta
authors.initials: C
authors.lastname: McManus
authors.affiliation: INCT - Pecuaria, Universidade Federal de Minas Gerais, 30161-970 Belo Horizonte, Brazil - Instituto Federal de Educação, Ciência e Tecnologia Goiano - Campus Iporá, Avenida Oeste s/n, saída para Piranhas, CEP 76.200-000 Iporá, Goiás, Brazil.
authors.forename: Tiago
authors.initials: T
authors.lastname: do Prado Paim
authors.affiliation: Universidade de Brasília, Campus Darcy Ribeiro, 70910-900 Asa Norte, Brasilia, Distrito Federal, Brazil - INCT - Pecuaria, Universidade Federal de Minas Gerais, 30161-970 Belo Horizonte, Brazil.
authors.forename: Cristiano Barros
authors.initials: CB
authors.lastname: de Melo
authors.affiliation: EMBRAPA Agroenergia, Final W3 Norte, 70770-901 Brasília, Brazil.
authors.forename: Bruno S A F
authors.initials: BS
authors.lastname: Brasil
authors.affiliation: Secretaria de Relações Internacionais, Embrapa, Final W5 Norte, 70770-901 Brasília, Brazil - EMBRAPA Recursos Genéticos e Biotecnologia, Final W5 Norte, 70770-901 Brasília, Brazil.
authors.forename: Samuel R
authors.initials: SR
authors.lastname: Paiva
mesh_terms: D000483:Alleles; D000822:Animal Husbandry / Q000379:methods*; D000818:Animals; D000871:Anthelmintics / Q000627:therapeutic use; D015415:Biomarkers; D001947:Breeding / Q000379:methods*; D060467:Disease Resistance / Q000235:genetics; D004351:Drug Resistance / Q000235:genetics; D019143:Evolution, Molecular; D059647:Gene-Environment Interaction; D056726:Genetic Association Studies / Q000662:veterinary; D005828:Genetics, Population; D055106:Genome-Wide Association Study / Q000662:veterinary; D015511:Goat Diseases / Q000188:drug therapy / Q000235:genetics / Q000517:prevention & control; D006041:Goats / Q000235:genetics / Q000469:parasitology; D006374:Helminthiasis, Animal / Q000188:drug therapy / Q000235:genetics / Q000517:prevention & control*; D006790:Host-Parasite Interactions / Q000235:genetics; D006801:Humans; D009154:Mutation; D010270:Parasite Egg Count; D040641:Quantitative Trait Loci; D012641:Selection, Genetic; D012756:Sheep / Q000235:genetics / Q000469:parasitology; D012757:Sheep Diseases / Q000188:drug therapy / Q000235:genetics / Q000517:prevention & control*; D013045:Species Specificity
chemical_list: D000871:Anthelmintics; D015415:Biomarkers