Elucidating the genetic basis of tick resistance in nguni cattle

• Published in: Journal of animal science 2016-09, Vol.94, p.72-72
• Main Authors: Mapholi, N O, Maiwashe, A A, Matika, O, Riggio, V, MacNeil, M D, Banga, C B, Taylor, J F, Dzama, K
• Format: Article
• Language: English
• Subjects: Acaricides; Agricultural economics; Amblyomma hebraeum; Animal models; Arachnids; Association analysis; Bovidae; Cattle; Cattle production; Chromosomes; Control methods; Deoxyribonucleic acid; DNA; Economics; Gene frequency; Genetic diversity; Genetic improvement; Genetics; Genomes; Heritability; Infestation; Marker-assisted selection; Normality; Perineum; Profitability; Quality control; Quantitative trait loci; Single-nucleotide polymorphism; Tick-borne diseases; Ticks
• ISSN: 0021-8812; 1525-3163

Ticks are an important constraint to cattle production, particularly in tropical and subtropical regions of the world. Acaricides are the primary method of tick control; however, their cost has a large, negative impact on farm profitability. Hence, there is a need to find alternative tick control methods, such as genetic improvement, that are more affordable and sustainable. Most cattle breeds indigenous to regions with high tick infestations possess some degree of natural resistance to ticks and tick-borne diseases. Objectives of this study were to estimate heritability of tick count and identify genomic regions associated with tick resistance in South African Nguni cattle. Tick-count data were from 586 Nguni cattle exposed to natural infestation from four herds located in different provinces of South Africa. Tick counts by species were collected for eight anatomical locations over a 2-yr period (2013 and 2014) and data for November, December and January were log10(x + 1) transformed to achieve normality and analyzed separately for each month. DNA was extracted from hair and blood samples and genotyped using the Illumina BovineSNP50 assay. After quality control (call rate > 90%, minor allele frequency > 2%), 40,436 SNPs were retained for analysis. Heritabilities were estimated using ASReml to fit animal models. A genome-wide association analysis for tick count was performed using GenABEL. Heritability estimates for the eight analyzed tick-count traits ranged from 0.04 ± 0.04 to 0.20 ± 0.04. Two genome-wide significant regions on Chr 1 and 19 were identified for total tick count on the perineum and for total body Amblyomma hebraeum ticks, respectively, and these have been previously identified. Additional regions significant at the suggestive level were identified on most chromosomes for several of the traits. The regions identified here as harboring QTL underlying variation in tick burden now enables candidate gene analyses to identify polymorphisms related to tick resistance for marker-assisted selection in Nguni cattle. There is significant genetic variation among cattle for tick counts, and this offers the potential to use genetic tick control approaches.