|BENAVIDES, MAGDA - Embrapa-Labex|
|KEMP, STEVE - International Livestock Research Institute (ILRI) - Kenya|
|MUGAMBI, JM - Kenya Agricultural Research Institute|
|GIBSON, JOHN - University Of New England|
|BAKER, RL - Agresearch|
|Van Tassell, Curtis - Curt|
Submitted to: PLoS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2015
Publication Date: 3/13/2015
Citation: Benavides, M., Sonstegard, T.S., Kemp, S., Mugambi, J., Gibson, J., Baker, R., Van Tassell, C.P. 2015. Red Maasai x Dorper resistance to gastrointestestinal parasite infections associated to a panel of SNPs. PLoS One. 10(4):e0122797.
Technical Abstract: Gastrointestinal (GI) parasitic infection is a main health constraint that affects small ruminant production. Anthelmintic drugs are used to control parasites, however long-term use led to selection pressure, resulting in parasite resistance against all current chemical interventions available in the market. The aim of this study is to identify polymorphisms strongly associated with sheep host resistance against gastrointestinal parasite infections. A double backcross population of Red Maasai and Dorper sheep from the International Livestock Research Institute (ILRI) was genotyped with the OvineSNP50K BeadChip. Data for average fecal egg counts (AVFEC), packed cell volume (AVPCV), and live weight (AVLWT) were adjusted for fixed effects prior to setting the threshold for the tails of the distributions (10% most resistant and 10% most susceptible lambs). Single nucleotide markers (SNPs) were filtered for minor allele frequency, call rates per marker, and Hardy-Weinberg equilibrium criteria using PLink. Genome-wide significance threshold were defined after 100,000 permutations on EMMAX. Association analyses were calculated using QxPak v5.05 and significant SNPs with -log10 p-values >=4 were observed on 6, 7, and 7 chromosomes and 7, 9, and 8 chromosomic regions were detected for AVPCV, AVLWT, and AVFEC, respectively. No SNP was relevant for more than one trait. A set of 7, 10 and 9 SNPs explained 28.6%, 19.4% and 21.8% of the phenotypic variation of those traits. As a practical result, a panel with such markers could be used in Red Maasai x Dorper breeding programs to select for more resistant sheep. However, to determine the causal mutations that define more resistant Red Maasai x Dorper sheep, further studies will focus on 4, 3, and 3 SNPs that explained 21.8%, 11.2% and 13.4% of the phenotypic variation for AVPCV, AVLWT, and AVFEC, respectively, after a classification tree was used to calculate the best haplotype combination among most significant SNPs.