Multiple Country and Breed Genomic Prediction of Tick Resistance in Beef Cattle

Abstract

Ticks cause substantial production losses for beef and dairy cattle. Cattle resistance to ticks is one of the most important factors affecting tick control, but largely neglected due to the challenge of phenotyping. In this study, we evaluate the pooling of tick resistance phenotyped reference populations from multi-country beef cattle breeds to assess the possibility of improving host resistance through multi-trait genomic selection. Data consisted of tick counts or scores assessing the number of female ticks at least 4.5 mm length and derived from seven populations, with breed, country, number of records and genotyped/phenotyped animals being respectively: Angus (AN), Brazil, 2,263, 921/1,156, Hereford (HH), Brazil, 6,615, 1,910/2,802, Brangus (BN), Brazil, 2,441, 851/851, Braford (BO), Brazil, 9,523, 3,062/4,095, Tropical Composite (TC), Australia, 229, 229/229, Brahman (BR), Australia, 675, 675/675, and Nguni (NG), South Africa, 490, 490/490. All populations were genotyped using medium density Illumina SNP BeadChips and imputed to a common high-density panel of 332,468 markers. The mean linkage disequilibrium (LD) between adjacent SNPs varied from 0.24 to 0.37 across populations and so was sufficient to allow genomic breeding values (GEBV) prediction. Correlations of LD phase between breeds were higher between composites and their founder breeds (0.81 to 0.95) and lower between NG and the other breeds (0.27 and 0.35). There was wide range of estimated heritability (0.05 and 0.42) and genetic correlation (-0.01 and 0.87) for tick resistance across the studied populations, with the largest genetic correlation observed between BN and BO. Predictive ability was improved under the old-young validation for three of the seven populations using a multi-trait approach compared to a single trait within-population prediction, while whole and partial data GEBV correlations increased in all cases, with relative improvements ranging from 3% for BO to 64% for TC. Moreover, the multi-trait analysis was useful to correct typical over-dispersion of the GEBV. Results from this study indicate that a joint genomic evaluation of AN, HH, BN, BO and BR can be readily implemented to improve tick resistance of these populations using selection on GEBV. For NG and TC additional phenotyping will be required to obtain accurate GEBV.

Transcriptional changes in the peripheral blood leukocytes from Brangus cattle before and after tick challenge with Rhipicephalus australis

“…Selection for host resistance to ectoparasites is a desirable approach in the beef cattle industry as part of the overall genetic improvement strategy for animal productivity and health [ 4 , 5 ]. Host resistance reduces the tick burden and therefore is a measurable phenotype, but in general, tick counts or scores are difficult to obtain, which constrains the ability to obtain large numbers of animal phenotypes for genetic improvement [ 9 ]. Although there is a heritable component for differences in host resistance, the dynamics of the host immune response also have an indispensable contribution, but these remain to be well defined [ 43 ].…”

“…The tick scoring scale used for this Brangus herd was as follows: 1 = 0–50 ticks, 2 = 50–100 ticks, 3 = 100–200 ticks, 4 = 200–300 ticks, 5 = more than 300 ticks, blank = not scored. Similar studies have used similar scoring methods for tick infestation phenotyping [ 9 , 74 ]. The scores represent an estimation of the number of female adult ticks (un/semi/fully engorged) found on one side of the animal’s body (Fig.…”

“…However, treating animals with synthetic acaricides raises concerns about potential residual effects in meat and milk for human consumption, as well as the challenge of the development of chemical resistance [ 7 , 8 ]. Genetic selection to improve host resistance to ectoparasites remains the most sustainable approach to minimise disease burden and enhance animal welfare in the cattle industry [ 5 , 9 , 10 ].…”

“…However, stable composite breeds ( B. indicus x B. taurus ) range widely from low to high host resistance as reported in Santa-Gertrudis [ 15 ], Bradford [ 16 ] and Brangus [ 17 ]. Targeting tick resistance in breeding programs is desirable, but measuring the phenotype requires collection of tick counts or scores on an individual animal basis, which is costly, laborious, and requires standardisation of exposure [ 5 , 9 ]. Hence, knowledge of the genes controlling this trait will contribute towards the strategic development of biomarker-assisted selection methods for tick resistant cattle.…”

Genetic Characterization and Population Connectedness of North American and European Dairy Goats

“…Combining data from genetically related populations can be an efficient strategy for enlarging training populations for genomic predictions (Berry et al, 2014;Cardoso et al, 2021). For instance, this has been performed in European dairy cattle populations through the Eurogenomics Consortium (www.…”