Estimation of genomic breed composition of individual animals in composite beef cattle

Three statistical models (an admixture model, linear regression, and ridge-regression BLUP) and two strategies for selecting SNP panels (uniformly spaced vs. maximum Euclidean distance of SNP allele frequencies between ancestral breeds) were compared for estimating genomic-estimated breed composition (GBC) in Brangus and Santa Gertrudis cattle, respectively. Animals were genotyped with a GeneSeek Genomic Profiler bovine low-density version 4 SNP chip. The estimated GBC was consistent among the uniformly spaced SNP panels, and values were similar between the three models. However, estimated GBC varied considerably between the three methods when using fewer than 10 000 SNPs that maximized the Euclidean distance of allele frequencies between the ancestral breeds. The admixture model performed most consistently across various SNP panel sizes. For the other two models, stabilized estimates were obtained with an SNP panel size of 20 000 SNPs or more. Based on the uniformly spaced 20K SNP panel, the estimated GBC was 69.8–70.5% Angus and 29.5–30.2% Brahman for Brangus, and 63.9–65.3% Shorthorn and 34.7–36.1% Brahman in Santa Gertrudis. The estimated GBC of ancestries for Santa Gertrudis roughly agreed with the pedigree-expected values. However, the estimated GBC in Brangus showed a considerably larger Angus composition than the pedigree-expected value (62.5%). The elevated Angus composition in the Brangus could be due to the mixture of some 1/2 Ultrablack animals (Brangus × Angus). Another reason could be the consequences of selection in Brangus cattle for phenotypes where the Angus breed has advantages.     

Aged mice have increased inflammatory monocyte concentration and altered expression of cell-surface functional receptors

The expression of monocyte cell-surface receptors represents one index of immune dysfunction, which is common with aging. Although mouse models of aging are prevalent, monocyte subset assessment is rare. Our purpose was to compare cell receptor expression on classic (CD115⁺/Gr-1^high) and non-classic (CD115⁺/Gr-1^low) monocytes from 80- or 20-week-old CD-1 mice. Three-colour flow cytometry was used to determine the concentration of monocyte subsets and their respective cell-surface expression of TLR2, TLR4, CD80, CD86, MHC II and CD54. These receptors were selected because they have been previously associated with altered monocyte function. Data were analysed with independent t-tests; significance was set at P < 0.05. Old mice had a greater concentration of both classic (258%, P = 0.003) and non-classic (70%, P = 0.026) monocytes. The classic : non-classic monocyte ratio doubled in old as compared with that in young mice (P = 0.006), indicating a pro-inflammatory shift. TLR4 (↓27%, P = 0.001) and CD80 (↓37%, P = 0.004) were decreased on classic monocytes from old as compared with those from young mice. TLR2 (↑24%, P = 0.002) and MHCII (↓21%, P = 0.026) were altered on non-classic monocytes from old as compared with those from young mice. The increased classic : non-classic monocyte ratio combined with changes in the cell-surface receptor expression on both monocyte subsets is indicative of immune dysfunction, which may increase age-associated disease risk.     

Association of CISH -292A/T genetic variant with hepatitis B virus infection

Cytokine-inducible SRC homology 2 domain protein (CISH) is a suppressor of cytokine signaling that controls interleukin-2 signaling pathway. We investigated the single nucleotide polymorphism (SNP) -292A>T in 473 Vietnamese hepatitis B virus (HBV) carriers and 416 healthy controls. CISH variants at -292A>T were associated to HBV infection (Allelic: OR, 1.22 95% CI, 1–1.49; P = 0.04; Recessive: OR, 1.69 95% CI 1.23–2.54; P = 0.007). A gene dose effect for the risk allele -292T was observed (P = 0.04). The level of interleukin 2 and liver enzymes such as alanine transaminase, aspartate transaminase, total bilirubin, and direct bilirubin were not associated to CISH polymorphism at position -292A>T This study associated the vital role of CISH SNP -292A>T variant to hepatitis B virus infection in a Vietnamese population.     

Genetic parameters of infectious bovine keratoconjunctivitis and its relationship with weight and parasite infestations in Australian tropical Bos taurus cattle

Background

Infectious bovine keratoconjunctivitis (IBK) or ‘pinkeye’ is an economically important ocular disease that significantly impacts animal performance. Genetic parameters for IBK infection and its genetic and phenotypic correlations with cattle tick counts, number of helminth (unspecified species) eggs per gram of faeces and growth traits in Australian tropically adapted Bos taurus cattle were estimated.

Methods

Animals were clinically examined for the presence of IBK infection before and after weaning when the calves were 3 to 6 months and 15 to 18 months old, respectively and were also recorded for tick counts, helminth eggs counts as an indicator of intestinal parasites and live weights at several ages including 18 months.

Results

Negative genetic correlations were estimated between IBK incidence and weight traits for animals in pre-weaning and post-weaning datasets. Genetic correlations among weight measurements were positive, with moderate to high values. Genetic correlations of IBK incidence with tick counts were positive for the pre-weaning and negative for the post-weaning datasets but negative with helminth eggs counts for the pre-weaning dataset and slightly positive for the post-weaning dataset. Genetic correlations between tick and helminth eggs counts were moderate and positive for both datasets. Phenotypic correlations of IBK incidence with helminth eggs per gram of faeces were moderate and positive for both datasets, but were close to zero for both datasets with tick counts.

Conclusions

Our results suggest that genetic selection against IBK incidence in tropical cattle is feasible and that calves genetically prone to acquire IBK infection could also be genetically prone to have a slower growth. The positive genetic correlations among weight traits and between tick and helminth eggs counts suggest that they are controlled by common genes (with pleiotropic effects). Genetic correlations between IBK incidence and tick and helminth egg counts were moderate and opposite between pre-weaning and post-weaning datasets, suggesting that the environmental and (or) maternal effects differ between these two growth phases. This preliminary study provides estimated genetic parameters for IBK incidence, which could be used to design selection and breeding programs for tropical adaptation in beef cattle.     

Mannose-binding lectin 1 haplotypes influence serum MBL-A concentration,complement activity,and milk production traits in Chinese Holstein cattle

Mannose-binding lectin (MBL) is a member of the collectin protein family that binds a broad range of microorganisms and activates the lectin-complement pathway of innate immunity. MBL deficiency is associated with an increased risk for various infections and arises from five polymorphisms in the promoter and first exon of the MBL gene in humans. In this study, three novel single-nucleotide polymorphisms (SNPs) in the promoter region and two previously reported SNPs in exon 2 of the MBL1 gene were detected using PCR single-strand conformation polymorphism, restriction fragment length polymorphism, and DNA sequencing in 537 cattle from three Chinese breeds. Analysis of the genotypes and haplotypes was used to investigate the polymorphisms and their possible implications, especially their association with serum MBL-A levels, complement activity (CH50 and ACH50), and milk production traits was investigated. The g.2651G>A SNP in exon 2 affected the serum MBL-A concentrations and the serum CH50 values, whereas the g.−1330G>A SNP significantly affected CH50 and the somatic cell scores (SCSs). Statistical analysis revealed that cows with the ATGGC/ACAAC combined genotype and those with the AAGGT/ACGGT combined genotype exhibited the lowest and highest SCSs, respectively. Serum antibacterial activities were also conducted to verify the effect of the SNPs on resistance to mastitis pathogens. Results of real-time PCR showed that the liver of cows with clinical mastitis exhibited a higher MBL1 expression compared with healthy ones (P < 0.05). Findings of this study indicate that the MBL1 gene possibly contributes to bacterial infection resistance and can be used as a molecular marker of milk production traits to control mastitis.     

A genome scan for quantitative trait loci influencing carcass,post‐natal growth and reproductive traits in commercial Angus cattle

To gain insight into the number of loci of large effect that underlie variation in cattle, a quantitative trait locus (QTL) scan for 14 economically important traits was performed in two commercial Angus populations using 390 microsatellites, 11 single nucleotide polymorphisms (SNPs) and one duplication loci. The first population comprised 1769 registered Angus bulls born between 1955 and 2003, with Expected Progeny Differences computed by the American Angus Association. The second comprised 38 half‐sib families containing 1622 steers with six post‐natal growth and carcass phenotypes. Linkage analysis was performed by half‐sib least squares regression with gridqtl or Bayesian Markov chain Monte Carlo analysis of complex pedigrees with loki . Of the 673 detected QTL, only 118 have previously been reported, reflecting both the conservative approach to QTL reporting in the literature, and the more liberal approach taken in this study. From 33 to 71% of the genetic variance and 35 to 56% of the phenotypic variance in each trait was explained by the detected QTL. To analyse the effects of 11 SNPs and one duplication locus within candidate genes on each trait, a single marker analysis was performed by fitting an additive allele substitution model in both mapping populations. There were 53 associations detected between the SNP/duplication loci and traits with ?log₁₀P_nominal≥ 4.0, where each association explained 0.92% to 4.4% of the genetic variance and 0.01% to 1.86% of the phenotypic variance. Of these associations, only six SNP/duplication loci were located within 8 cM of a QTL peak for the trait, with two being located at the QTL peak: SST_DG156121:c.362A>G for ribeye muscle area and TG_X05380:c.422C>T for calving ease. Strong associations between several SNP/duplication loci and trait variation were obtained in the absence of any detected linked QTL. However, we reject the causality of several commercialized DNA tests, including an association between TG_X05380:c.422C>T and marbling in Angus cattle.     

Association of TLR4 polymorphisms with Mycobacterium avium subspecies paratuberculosis infection status in Canadian Holsteins

Mycobacterium avium ssp. paratuberculosis (MAP) causes chronic enteritis in cattle that results in substantial financial losses to the cattle industry worldwide. Given that susceptibility to MAP infection is determined in part by genetics, marker‐assisted selection may help in the breeding of animals that are more resistant to MAP infection. The toll‐like receptor 4 gene (TLR4) was selected as a potential candidate gene because of its role in innate immunity and its involvement in MAP recognition and infection. The objective of this study, therefore, was to identify associations between TLR4 polymorphisms and susceptibility to MAP infection in Canadian Holstein cows. Two biologically relevant SNPs, including c.‐226G>C in the 5′‐untranslated region and the non‐synonymous SNP c.2021C>T in the potential TIR domain, were selected for an association analysis with MAP infection status in 409 Canadian Holsteins. The haplotype C‐T from these combined SNPs yielded significant association with susceptibility to MAP infection, supporting the involvement of TLR4 in susceptibility to MAP infection.     

Toll-like receptor 8 polymorphism and coronary artery disease

Toll-like receptors (TLRs) play roles in innate and adaptive immune responses. Some TLRs are involved in the pathogenesis of cardiovascular diseases. Coronary artery disease (CAD) has an inflammatory and immunological basis. We investigated whether TLR8 Met1Val and TLR8-129G>C single nucleotide polymorphisms (SNPs rs3764879 and rs3764880) are associated with CAD in the Chinese population. We enrolled 412 consecutive patients (185 with coronary stenosis ≥50% or previous myocardial infarction and 227 controls). Ligase detection reaction was performed to detect SNPs rs3764879 and rs3764880 of TLR8. The SNP at rs3764879 is in complete linkage disequilibrium with rs3764880. No significant difference was found in genotypic or allelic frequencies of these two common SNPs between CAD cases and controls (P > 0.05, respectively). No associations existed between these two SNPs and the severity of coronary artery stenosis (All P > 0.05). These results do not support an involvement of SNPs rs3764879 and rs3764880 of TLR8 in predisposition to CAD. Z. Chen and G. Ma contributed equally to this paper.     

Reduced cardiac stiffness following exercise is associated with preserved myocardial collagen characteristics in the rat

We determined whether the increment in cardiac end-diastolic compliance (a reduced diastolic stiffness constant) following endurance training is related to alterations in myocardial collagen characteristics. Sixteen weeks of habitual exercise (Ex) in rats, which produced left ventricular (LV) hypertrophy (LVH) [LV weight in g: Ex=1.01 (0.04), sedentary control = 0.89 (0.04); P<0.05], resulted in a reduced LV end-diastolic (LVED) chamber stiffness [slope of the linearised LVED pressure versus LVED internal diameter relation in kPa · mm⁻¹: Ex=0.67 (0.03), control=0.80 (0.03); P<0.05]. The increased LVED chamber distensibility was associated with an attenuated myocardial stiffness [slope of the linearised LVED stress versus strain relation in g · cm⁻²; Ex=15 (3), control=25 (2); P<0.05]. Although LV total collagen content (mg) was increased in the exercised rats [Ex=5.0 (0.3), control=4.1 (0.2); P<0.05], this was a reflection of the presence of LVH, as the myocardial collagen concentration (μg · mg⁻¹ LV wet weight) was unaltered [Ex=4.9 (0.2), control=4.6 (0.2)]. Furthermore, habitual exercise did not influence the percentage of myocardial collagen extracted following cyanogen bromide digestion (an index of collagen cross-linking), [i.e. Ex=38 (3), control=38 (3)], nor the proportion of myocardial collagen phenotypes I and III [I/III; Ex=3.04 (0.20), control=2.85 (0.22)]. In conclusion, exercise-induced increments in end-diastolic myocardial distensibility are unlikely to be a consequence of alterations in the properties of myocardial collagen. Accepted: 17 December 1997     

The effect of body weight on some welfare indicators in feedlot cattle in a hot environment

Heat stress has important effects on the welfare of livestock. The effects of heat stress in cattle include changes in biological functions and behaviors. The aim of this study was to investigate the behavioral differences between light and heavy feedlot cattle reared in a hot environment. Sixteen male Holstein feedlot cattle were allocated to light (353.8 ± 15.5 kg, n = 8) and heavy (737.1 ± 15.8 kg, n = 8) groups according to their live weight and were kept in a semi-open feedlot barn. The individual behavioral response variables measured were standing, lying, feeding, drinking, ruminating, locomotor activity and elimination (urinating and defecating). The effects of group, day, observation time, replicate and all interactions were included in an explanatory statistical (GLM) model. The data were analyzed using the PROC GLM procedure of SAS. Overall, the heavy cattle spent more time standing (P < 0.001), lying (P < 0.001), and eliminating (P < 0.05) compared to the light group. In contrast, the light group spent more time eating, drinking and ruminating (P < 0.001). Locomotor activity did not differ significantly between groups (P > 0.05). During the day, heavy cattle spent more time standing (at 1600 hours) and less time eating in comparison with the light cattle (P < 0.001) (at 1300 and 1600 hours). Light and heavy feedlot cattle behaved differently in a hot environment. The findings of the study indicate that the welfare of the heavy Holstein feedlot cattle was impacted negatively when the ambient temperature was high (at 1300 hours).     

Genotype frequency and F ST analysis of polymorphisms in immunoregulatory genes in Chinese and Caucasian populations

Selection and genetic drift can create genetic differences between populations. Cytokines and chemokines play an important role in both hematopoietic development and the inflammatory response. We compared the genotype frequencies of 45 SNPs in 30 cytokine and chemokine genes in two healthy Chinese populations and one Caucasian population. Several SNPs in IL4 had substantial genetic differentiation between the Chinese and Caucasian populations (F _ST ~0.40), and displayed a strikingly different haplotype distribution. To further characterize common genetic variation in worldwide populations at the IL4 locus, we genotyped 9 SNPs at the IL4 gene in the Human Diversity Panel’s (N = 1056) individuals from 52 world geographic regions. We observed low haplotype diversity, yet strikingly different haplotype frequencies between non-African populations, which may indicate different selective pressures on the IL4 gene in different parts of the world. SNPs in CSF2, IL6, IL10, CTLA4, and CX3CR1 showed moderate genetic differentiation between the Chinese and Caucasian populations (0.15 < F _ST < 0.25). These results suggest that there is substantial genetic diversity in immune genes and exploration of SNP associations with immune-related diseases that vary in incidence across these two populations may be warranted.     

Bovine CLEC7A genetic variants and their association with seropositivity in Johne's disease ELISA

Mycobacterium avium ssp. paratuberculosis (MAP) infection in cattle causes significant economic losses to the dairy and beef industries resulting from reduced productivity, premature culling and mortality. Bovine Dectin-1, an important pattern recognition molecule that is able to generate a proinflammatory response by acting alongside Toll like receptor (TLR) signaling, is known to co-operate with TLR2 to specifically activate a macrophage proinflammatory response against mycobacterial infections. Therefore, the goal of this study was to identify single nucleotide polymorphisms (SNPs) in the gene encoding bovine Dectin-1 (CLEC7A) and to assess their association with susceptibility to MAP infection in dairy cattle. Blood and milk samples, collected from commercial dairy operations, were tested for MAP infection using blood and milk ELISAs and a resource population consisting of 197 infected and 242 healthy cattle was constructed. Pooled DNA was used for sequencing and eight single nucleotide polymorphisms (SNPs) were identified. Identified SNPs were genotyped on the resource population using the iPLEX MassARRAY system and statistical analysis was performed using logistic regression fitting the additive and dominance effects of each SNP in the model. Out of a total of eight identified SNPs, five were successfully genotyped, and three out of these five SNPs were found to be in complete linkage. Statistical analysis revealed a strong association between a non-synonymous SNP c.589A>G (p = 0.008), and MAP infection status of the resource population inferred by seropositivity in MAP antibody specific ELISAs. This SNP c.589A>G was located in the geneic region that encodes the carbohydrate recognition domain of bovine Dectin-1. Therefore, further investigation of its functional relevance is warranted.     

Rubella vaccine-induced cellular immunity: evidence of associations with polymorphisms in the Toll-like, vitamin A and D receptors, and innate immune response genes

Toll-like, vitamin A and D receptors and other innate proteins participate in various immune functions. We determined whether innate gene-sequence variations are associated with rubella vaccine-induced cytokine immune responses. We genotyped 714 healthy children (11–19 years of age) after two doses of rubella-containing vaccine for 148 candidate SNP markers. Rubella virus-induced cytokines were measured by ELISA. Twenty-two significant associations (range of P values 0.002–0.048) were found between SNPs in the vitamin A receptor family (RARA, RARB, TOP2B and RARG), vitamin D receptor and downstream mediator of vitamin D signaling (RXRA) genes and rubella virus-specific (IFN-γ, IL-2, IL-10, TNF-α, and GM-CSF) cytokine immune responses. A TLR3 gene promoter region SNP (rs5743305, −8441A > T) was associated with rubella-specific GM-CSF secretion. Importantly, SNPs in the TRIM5 gene coding regions, rs3740996 (His43Tyr) and rs10838525 (Gln136Arg), were associated with an allele dose-related secretion of rubella virus-specific TNF-α and IL-2/GM-CSF, respectively, and have been previously shown to have functional consequences regarding the antiviral activity and susceptibility to HIV-1 infection. We identified associations between individual SNPs and haplotypes in, or involving, the RIG-I (DDX58) gene and rubella-specific TNF-α secretion. This is the first paper to present evidence that polymorphisms in the TLR, vitamin A, vitamin D receptor, and innate immunity genes can influence adaptive cytokine responses to rubella vaccination.     

Genetic Polymorphisms in the Bovine Toll-Like Receptor 4 (TLR4) and Monocyte Chemo Attractant Protein-1(CCL2) Genes: SNPs Distribution Analysis in Bos indicus Sahiwal Cattle Breed

Toll-like receptor 4 gene (TLR4) that recognizes the Gram negative bacterial ligand LPS was sequenced in the Bos indicus Sahiwal cattle breed. Ninety four single nucleotide polymorphisms (SNPs) were detected within 10.8 kb gene region. Seventeen of the SNPs were in the coding regions and the one at position 9589(A > G) in exon3 resulted in an amino acid change from Valine to Isoleucine. These SNPs led to generation of 27 TLR4 gene haplotypes. All the Sahiwal animals studied presently showed the occurrence of the genotype CC at gene position 9662, which codes for the amino acid threonine at position 674 of the TLR4 protein, and which had been reported to be associated with lower somatic cell score and, therefore, a lower susceptibility to mastitis, in Taurus cattle. This nucleotide configuration of the Toll-like receptor 4 gene of the Bos indicus Sahiwal cattle breed could possibly indicate toward a lower susceptibility to mastitis in the Sahiwal animals. Monocyte chemo-attractant protein-1 (CCL2) gene encoding for small inducible cytokine A2 that belongs to the CC chemokine family was also sequence characterized in these Sahiwal animals. The CCL2 gene was observed to have 12 polymorphic sites in 3.3 kb region of which one SNP at position 2500 (A > G) in exon 3 resulted in amino acid change from Valine to Isoleucine at position 46 of the mature CCL2 peptide. Seventeen haplotypes of the CCL2 gene were predicted corresponding to 12 genotypes detected.     

Reproductive tissue-specific expression profiling and genetic variation across a 19 gene bovine β-defensin cluster

β-defensins are small cationic peptides, with potent immunoregulatory and antimicrobial activity which are produced constitutively and inducibly by eukaryotic cells. This study profiles the expression of a cluster of 19 novel defensin genes which spans 320 kb on chromosome 13 in Bos taurus. It also assesses the genetic variation in these genes between two divergently selected cattle breeds. Using quantitative real-time PCR (qRT-PCR), all 19 genes in this cluster were shown to be expressed in the male genital tract and 9 in the female genital tract, in a region-specific manner. These genes were sequenced in Norwegian Red (NR) and Holstein-Friesian (HF) cattle for population genetic analysis. Of the 17 novel single nucleotide polymorphisms (SNPs) identified, 7 were non-synonymous, 6 synonymous and 4 outside the protein coding region. Significant frequency differences in SNPs in bovine β-defensins (BBD) 115, 117, 121, and 122 were detected between the two breeds, which was also reflected at the haplotype level (P < 0.05). There was clear segregation of the haplotypes into two blocks on chromosome 13 in both breeds, presumably due to historical recombination. This study documents genetic variation in this β-defensin gene cluster between Norwegian Red and Holstein-Friesian cattle which may result from divergent selection for production and fertility traits in these two breeds. Regional expression in the epididymis and fallopian tube suggests a potential reproductive-immunobiology role for these genes in cattle.     

Associations of polymorphisms in the promoter I of bovine acetyl‐CoA carboxylase‐α gene with beef fatty acid composition

The objectives of this study were to identify single nucleotide polymorphisms (SNPs) in the promoter I (PI) region of the bovine acetyl‐CoA carboxylase‐α (ACACA) gene and to evaluate the extent to which they were associated with lipid‐related traits. Eight novel SNPs were identified, which were AJ276223:g.2064T>A (SNP1), g.2155C>T (SNP2), g.2203G>T (SNP3), g.2268T>C (SNP4), g.2274G>A (SNP5), g.2340A>G (SNP6), g.2350T>C (SNP7) and g.2370A>G (SNP8). Complete linkage disequilibrium was observed among SNP1, 2, 4, 5, 6 and 8. Phenotypic data were collected from 573 cross‐bred steers with six sire breeds, including Hereford, Angus, Brangus, Beefmaster, Bonsmara and Romosinuano. The genotypes of SNP1/2/4/5/6/8 were significantly associated with adjusted backfat thickness. The genotypes of SNP3 were significantly associated with triacylglycerol (TAG) content and fatty acid composition of longissimus dorsi muscle (LM) in Brangus‐, Romosinuano‐ and Bonsmara‐sired cattle. Cattle with g.2203GG genotype had greater concentrations of TAG, total lipid, total saturated fatty acid and total monounsaturated fatty acid than did cattle with g.2203GT genotype. The genotypes of SNP7 were significantly associated with fatty acid composition of LM. Cattle with genotype g.2350TC had greater amounts of several fatty acids in LM than did cattle with genotype g.2350CC. Our results suggested that the SNPs in the PI region of ACACA gene are associated with variations in the fatty acid contents in LM.     

Identification of quantitative trait loci affecting gastrointestinal parasite resistance in an experimental Angus population

DNA markers associated with quantitative trait loci (QTL) affecting host tolerance to gastrointestinal (GI) parasite infection are ideal targets for marker‐assisted selection. However, few studies in cattle have attempted to identify this type of QTL due to the difficulty of generating accurate phenotypic data from a resource population with adequate statistical power for detection. For this effort, we amassed fecal egg count (FEC) measures from annual natural field challenges with GI nematodes that spanned 12 different contemporary groups of Angus calves (1992–2000) derived from a closed breeding population. FEC and blood pepsinogen measures were taken weekly over a 26‐week period post‐weaning, and the FEC data were Box‐Cox transformed to normalize the distribution of phenotypes. These 305 test animals and more than 100 founding animals from the extended pedigree were genotyped across 190 microsatellites markers. The genome‐wide analyses identified a suggestive genome‐wide QTL on bovine chromosome (Chr) 8 (P < 0.002) and nominal QTL on Chr 4, 12 and 17 (P < 0.05). These findings were unique for cattle, and some corresponded to previously identified QTL locations for parasite‐related traits in sheep to provide genome locations for further fine mapping of parasite resistance/susceptibility in Angus cattle.     

The <Emphasis Type="Italic">RIPK2</Emphasis> gene: a positional candidate for tick burden supported by genetic associations in cattle and immunological response of knockout mouse

Ticks and tick-borne diseases have a detrimental impact on livestock production causing estimated losses of around $200 million per year in Australia alone. Host resistance to ticks is heritable, within-breed heritability estimates being around 0.35, and with large differences between breeds. Previously a QTL for tick burden was detected on BTA14 at ~72 Mb distal to the centromere, near the gene receptor-interacting serine-threonine kinase 2 (RIPK2). To identify polymorphisms in this region, we sequenced all exons of the RIPK2 gene, identifying 46 single nucleotide polymorphism (SNP). Using SNP from RIPK2 as well as SNP from the bovine genome sequence, we genotyped two samples, one of 1,122 taurine dairy cattle and one of 761 zebu and zebu composite beef cattle. We confirmed that SNP and haplotypes from this region, including from RIPK2, were associated with tick burden in both dairy and beef cattle. To determine whether RIPK2 influences response to tick salivary gland extract (SGE), an immunisation experiment with tick SGE in a RIPK2 knockout (RIPK2 −/−) mouse strain was conducted. There was a significant (P < 0.05) reduction in IgG production in the RIPK2 −/− mouse in response to the SGE compared to its background strain C57BL/6 as well as the outbred CD1 mouse strain. In addition, antibodies generated by RIPK2 −/− mice recognised a different set of antigens within SGE when compared to parental-derived antibodies. In summary, the SNP association with tick burden at BTA14 was confirmed and quantitative and qualitative differences in antibody production were observed between RIPK2 −/− and wild-type mice.