Identification of Bovine genomic regions potentially responsible for resistance to widespread Bovine Leukaemia Virus infections in Dairy cattle

HUGO CARIGNANO; DANA ROLDAN; MARIA AGUSTINA RASCHIA; MARIA JOSE BERIBE; GERÓNIMO GUTIERREZ; IRENE ALVAREZ; ARIEL AMADIO; MARIO POLI; KARINA TRONO; MARIO POLI

Sao Pablo

Simposio; 5th International Symposium on Animal Functional Genomics; 2013

Introduction: BLV is a serious animal health problem worldwide. In Argentina, dairy farms are burdensomely infected with BLV causing important economic losses. Control measures were implemented elsewhere in order to reduce prevalence based mainly in eradication/segregation of infected cattle and vaccination. In countries with high prevalence of infection these efforts were unsuccessful due mostly to economic costs, management restrictions and lack of an efficient vaccine. Is of prime importance to develop novel strategies to control BLV infection. Livestock breeding programs exploit selection of genetic traits beneficial for production (e.g., milk traits, growth, reproduction). In this context, the implementation of programs that include resistance to diseases have the potential to be useful as complementary tools of control. Objective: The aim of this presentation is to show briefly the experimental design and tasks that will be carried out in order to obtain information about genes and genomics regions (loci) involved in prevalence and pathobiology of BLV infection using high densities SNPs markers. Methods: The population consist of 999 Holstein and Holstein x Jersey crosses cows belonging to commercial breeds located in a dairy farms area from Argentina with high prevalence to BLV infection. The population under study is distributed in 29 half-sib families with complete genealogical information spanning several generations. Genome-wide association (GWA) analysis will be performed using different phenotype definitions. The prevalence for all samples was determinated on the presence of anti-p24 antibodies trough a test ELISA using recombinant BLV-p24 viral core protein (ELISA-p24). The humoral immune response level induced in natural conditions was measured trough the total white blood cell count (WBC) and p24 antibody reactivity. The infection level in vivo was evaluated by quantification of blood proviral load using real-time PCR. Animals will be catalogued as "cases" / "controls" using different disease phenotype classifications. The definition of various extreme phen otypes may explain the different genetic loci potentially involved in the susceptibility at different stages during the dynamic of infection. Genome-wide association analysis will be performed using the GRAMMAR-CG approach. Each animal was enotyped using the BovineSNP50 BeadChip with 54,609 SNPs. After quality assurance filtering recently conducted, 925 animals and 44,163 SNPs remained. Conclusions: To our knowledge, this will be the first GWA study of Bovine leukemia virus infection in cattle using the Bovine 50K Chip. Regarding that BLV infection control in dairy farms remains difficult, the dentification of loci associated with susceptibility/resistance could be included into breeding schemes. Even more, understanding the function exerted by the products of these loci, could enable the development of novel therapeutic strategies, effective vaccines and diagnostic tools.