Selection For Mastitis Resistance Research Articles

Kompetitive Allele Specific PCR Genotyping of 89 SNPs in Romanian Spotted and Romanian Brown Cattle Breeds and Their Association with Clinical Mastitis.

Mastitis is the most common production disease in the dairy sector worldwide, its incidence being associated with both cows' exposure to bacteria and the cows' genetic make-up for resistance to pathogens. The objective of our study was to analyse 89 missense SNPs belonging to six genes (CXCR2, CXCL8, TLR4, BRCA1, LTF, BOLA-DRB3), which were found to be associated with genetic resistance or susceptibility to mastitis. A total of 298 cattle (250 Romanian Spotted and 48 Romanian Brown) were genotyped by Kompetitive Allele Specific PCR (KASP) and a chi-squared test was used for genetic association studies with clinical mastitis. A total of 35 SNPs (39.3%) among the selected 89 SNPs were successfully genotyped, of which 31 markers were monomorphic. The polymorphic markers were found in two genes: TLR4 (rs460053411) and BOLA-DRB3 (rs42309897, rs208816121, rs110124025). The polymorphic SNPs with MAF > 5% and call rates > 95% were used for the association study. The results showed that rs110124025 in the BOLA-DRB3 gene was significantly associated with mastitis prevalence (p ≤ 0.05) in both investigated breeds. Current results show that the SNP rs110124025 in the BOLA-DRB3 gene can be used as a candidate genetic marker in selection for mastitis resistance in Romanian dairy cattle.

Antibiotic treatments and somatic cell count as phenotype to map QTL for mastitis susceptibility in Holstein cattle breed

Mastitis is one of the most significant diseases affecting dairy cattle profitability. A genome wide association study (GWAS) was performed using the selective genotyping approach to identify Quantitative Trait Loci (QTL) associated with mastitis susceptibility. According to the received antibiotic treatments in all their productive life, 52 lactating cows have been classified in resistant (no therapy and low SCC) and susceptible (more than one treatment and high SCC) to mastitis. Genotyping of animals was performed using the NEOGEN’s GGP Bovine 100K SNP chip and QTL were identified comparing the SNPs allelic frequencies between the two groups. 26 SNPs related to mastitis susceptibility were identified in 9 chromosomes. The use of treatment data, coupled with SCC from milk recording, improved cow’s classification accuracy in resistant and susceptible individuals. For this reason, the mandatory recording of treatments active from January 2022, could be a new source of information to improve the genetic selection for mastitis resistance.

Estimation of genotype by temperature-humidity index interactions on milk production and udder health traits in Montbeliarde cows

BackgroundHeat stress negatively influences cattle welfare, health and productivity. To cope with the forecasted increases in temperature and heat waves frequency, identifying high-producing animals that are tolerant to heat is of capital importance to maintain milk production. This study, based on the joint analysis of on-farm performance and weather data, had two objectives: (1) to determine the response in production performances (milk, fat and protein yields, fat and protein contents) and udder health (somatic cell score) to temperature-humidity index (THI) variations in Montbeliarde cows, and (2) to estimate the interactions between genotype and THI, to enable the identification of the most adapted animals for facing the expected increases in temperature.ResultsTest-day records from first and second lactations from 2016 to 2020 were associated with the average THI during the three days before the test-day record. In total, 446,717 test-day records from 55,650 cows in first lactation and 457,516 test-day records from 58,229 cows in second lactation were analysed. The optimal THI was below 55 (i.e. ~ 12–13 °C) for all traits. Individual responses to THI were estimated by random regression models, which also included individual responses to days in milk. Regardless of the stage of lactation, genetic correlations along the THI gradient were above 0.80, which suggests that genotype-by-THI interactions were weak for production and udder health traits. Nevertheless, a variability in the individual slope of decay could be highlighted at high THI. The genetic correlation between production level at moderate THI and the slope at high THI was negative, while for somatic cell score, it was positive, indicating that heat stress amplifies the susceptibility to mastitis.ConclusionsThe optimal THI for French Montbeliarde cows is below 55 for production and udder health traits. Genetic-by-THI interactions are weak in French Montbeliarde cows for production and udder health traits, but not all animals react in the same way to high temperatures. Even if there is little room for improvement, using a heat tolerance index in cattle selection would be relevant to anticipate the expected increases in temperature. Further investigations are needed to interpret this variability on production traits. However, the current selection for mastitis resistance seems appropriate to adapt cattle to rising temperatures.

Lactoferrin gene polymorphisms associated with clinical mastitis in Honduran Holstein inheritance cows.

Lactoferrin (LTF) is an iron-binding glycoprotein found in milk and other exocrine secretion with antibacterial activity proposed as an alternative to mastitis treatment or prevention. LTF has been proposed as a candidate gene for mastitis resistance selection. The aim of this paper was to assess LTF promotor to explore variations with potential association to mastitis resistance in dairy cows from Honduras. A resequencing of promotor and Exon I of LTF gene in extreme mastitis susceptibility cows (126 Holstein and Holstein crossbred) was performed. Eight polymorphisms were found in promotor region, four of them were novel variations. Two were important by frequency among extreme groups, but a polymorphism in - 421 A/T position was significantly (P = 0.0188) associated to mastitis susceptibility. Results support the key role of regulatory region of LTF gene. Some candidate genes are proposed in association with mastitis traits and implications are discussed.

Validation of somatic cell score-associated SNPs from Holstein cattle in Sudanese Butana and Butana\u2009\xd7\u2009Holstein crossbred cattle

The Bos indicus zebu cattle Butana is the most commonly used indigenous dairy cattle breed in Sudan. In the last years, high-yielding Holstein dairy cattle were introgressed into Butana cattle to improve their milk yield and simultaneously keep their good adaption to extreme environmental conditions. With the focus on the improvement of milk production, other problems arose such as an increased susceptibility to mastitis. Thus, genetic selection for mastitis resistance should be considered to maintain healthy and productive cows. In this study, we tested 10 single nucleotide polymorphisms (SNPs) which had been associated with somatic cell score (SCS) in Holstein cattle for association with SCS in 37 purebred Butana and 203 Butana × Holstein crossbred cattle from Sudan. Animals were genotyped by competitive allele-specific PCR assays and association analysis was performed using a linear mixed model. All 10 SNPs were segregating in the crossbred Butana × Holstein populations, but only 8 SNPs in Sudanese purebred Butana cattle. The SNP on chromosome 13 was suggestively associated with SCS in the Butana × Holstein crossbred population (rs109441194, 13:79,365,467, PBF = 0.054) and the SNP on chromosome 19 was significantly associated with SCS in both populations (rs41257403, 19:50,027,458, Butana: PBF = 0.003, Butana × Holstein: PBF = 6.2 × 10−16). The minor allele of both SNPs showed an increase in SCS. Therefore, selection against the disadvantageous minor allele could be used for genetic improvement of mastitis resistance in the studied populations. However, investigations in a bigger population and across the whole genome are needed to identify additional genomic loci.

Identification of SNPs Associated with Somatic Cell Score in Candidate Genes in Italian Holstein Friesian Bulls.

Simple SummaryMastitis is a worldwide diffused disease usually treated with an excessive use of antibiotics. Therefore, antimicrobial resistance is an important issue to be addressed by scientists. One of the possible solutions to decrease the use of drugs is genetic selection of resistant animals, that is, individuals that can be more resistant to mastitis. In our survey we analyzed Single Nucleotide Polymorphisms (SNPs) in genes known to be involved in both infection resistance and immune system activity. We found a group of SNPs that can be associated to mastitis related phenotypes (namely SCS) and that can be used for selecting resistant animals. An efficient selection is able to improve both animal welfare and quality and safety of animal productsMastitis is an infectious disease affecting the mammary gland, leading to inflammatory reactions and to heavy economic losses due to milk production decrease. One possible way to tackle the antimicrobial resistance issue stemming from antimicrobial therapy is to select animals with a genetic resistance to this disease. Therefore, aim of this study was to analyze the genetic variability of the SNPs found in candidate genes related to mastitis resistance in Holstein Friesian bulls. Target regions were amplified, sequenced by Next-Generation Sequencing technology on the Illumina® MiSeq, and then analyzed to find correlation with mastitis related phenotypes in 95 Italian Holstein bulls chosen with the aid of a selective genotyping approach. On a total of 557 detected mutations, 61 showed different genotype distribution in the tails of the deregressed EBVs for SCS and 15 were identified as significantly associated with the phenotype using two different approaches. The significant SNPs were identified in intergenic or intronic regions of six genes, known to be key components in the immune system (namely CXCR1, DCK, NOD2, MBL2, MBL1 and M-SAA3.2). These SNPs could be considered as candidates for a future genetic selection for mastitis resistance, although further studies are required to assess their presence in other dairy cattle breeds and their possible negative correlation with other traits.

Combining total and differential somatic cell count to screen for mastitis

Combining total and differential somatic cell count to screen for mastitis

ОПРЕДЕЛЕНИЕ И ИСПОЛЬЗОВАНИЕ ИНДЕКСОВ ПЛЕМЕННОЙ ЦЕННОСТИ БЫКОВ ПО СОМАТИЧЕСКИМ КЛЕТКАМ МОЛОКА У ДОЧЕРЕЙ ПРИ ОТБОРЕ НА РЕЗИСТЕНТНОСТЬ К МАСТИТУ

A method has been developed for determining and using bulls breeding value indices by the number of somatic cells in daughters’ milk during selection for mastitis resistance. The development is based on the investigation of somatic cells number (NSC) in 24800 milk samples of Ayrshire cows of the «Megrega» breeding plant, Republic of Karelia. The average lactational milk yield of cows in the herd was about 8300 kg of milk. For one bull an average 676 assessments of NSC in milk of daughters were made. The calculations used the logarithmic (scoring estimation) NSC. The transformation of absolute NSC (ANSC) in thousand / cm 3 into a scoring estimation (SE NSC) was carried out on the basis of the binary logarithm. Breeding Value Index (BVI) of bulls was calculated by comparing SE NSC of daughters and populations. At the same time, the number of cows-peers and the size of the population were taken into account; the heritability coefficients and the repeatability (regression) coefficients of the indicators for the future daughters of this bull on indicators of existing daughters were determined for specific conditions. Examined bulls were different in BVI. Since selection by health indicators, including mastitis, should be carried out to reduce the value of the indicator, then in this situation the best are the bulls with the minimum values of SE NSC and negative values of the breeding index. The three best sires had a BVI of less than minus one, the three worst ones had more than plus two. The scale has been developed for the distribution of estimated bulls by BVI on breeding categories - effective improvers of the 1st category (BVI is less than the population average by 1σ or more), improvers of the 2nd category (from - 0.4 σ to - 0.9 σ), neutral (+ 0.3 σ), deteriorators (from + 0.4 σ to + 0.9 σ), extreme deteriorators (+1 σ and more). Sires with a high BVI (- 1.012 or less) are selected for breeding use, rejected with a low BVI (+ 1.102 or more). In the studied bulls’ population, the share of 1-st category improvers was 11.1%, 2-nd category - 27.8%, neutral - 22.2%, and extreme deteriorators - 16.7%. Using the method can improve the objectivity and accuracy of selecting bulls for resistance, increase in the concentration of mastitis resistance genes in herds, and decrease the frequency of udder diseases.

Alternative somatic cell count traits exploitable in genetic selection for mastitis resistance in Italian Holsteins

The aim of the present study was to characterize alternative somatic cell count (SCC) traits that could be exploited in genetic selection for mastitis resistance. Data were from 66,407 first-parity Holsteins in 404 herds. Novel SCC traits included average somatic cell score (SCS, log-transformation of SCC) in early lactation (SCS_150), standard deviation of SCS of the entire lactation (SCS_SD), the presence of at least one test-day (TD) SCC >400,000 cells/mL in the lactation, and the ratio of number of TD SCC >400,000 cells/mL to total number of TD in the lactation. Novel traits and lactation-mean SCS (SCS_LM) were analyzed using linear mixed or logistic regression models, including month of calving, year of calving, number of TD, and milk yield as fixed effects, and herd and residual as random terms. A multitrait linear animal model was applied to a random subset of 152 herds (n = 22,695 cows) to assess heritability of and genetic correlations between SCC traits. Alternative SCC traits were affected by the environmental factors included in the model; in particular, results suggested a seasonal effect and a tendency toward an improvement of the udder health status in the last years. Association was also found between novel SCC traits and milk production. Alternative SCC traits exhibited coefficients of additive genetic variation that were similar to or larger than that of traditional SCS_LM. Heritability of novel SCC traits was smaller than heritability of SCS_LM (0.126 ± 0.014), ranging from 0.044 ± 0.008 (SCS_SD) to 0.087 ± 0.010 (SCS_150). Genetic correlations between SCC traits ranged from 0.217 ± 0.096 (SCS_150 and SCS_SD) to 0.969 ± 0.010 (SCS_LM and SCS_150). Alternative SCC traits exhibited additive genetic variation that is potentially exploitable in breeding programs of Italian Holstein population to improve resistance to mastitis.

Symposium review: Novel strategies to genetically improve mastitis resistance in dairy cattle

Mastitis is a disease of major economic importance to the dairy cattle sector because of the high incidence of clinical mastitis and prevalence of subclinical mastitis and, consequently, the costs associated with treatment, production losses, and reduced animal welfare. Disease-recording systems compiling data from a large number of farms are still not widely implemented around the world; thus, selection for mastitis resistance is often based on genetically correlated indicator traits such as somatic cell count (SCC), udder depth, and fore udder attachment. However, in the past years, several countries have initiated collection systems of clinical mastitis, based on producers recording data in most cases. The large data sets generated have enabled researchers to assess incidence of this disease and to investigate the genetic background of clinical mastitis itself, as well as its relationships with other traits of interest to the dairy industry. The genetic correlations between clinical mastitis and its previous proxies were estimated more accurately and confirmed the strong relationship of clinical mastitis with SCC and udder depth. New traits deriving from SCC were also studied, with the most relevant findings being associated with mean somatic cell score (SCS) in early lactation, standard deviation of SCS, and excessive test-day SCC pattern. Genetic correlations between clinical mastitis and other economically important traits indicated that selection for mastitis resistance would also improve resistance against other diseases and enhance both fertility and longevity. However, milk yield remains negatively correlated with clinical mastitis, emphasizing the importance of including health traits in the breeding objectives to achieve genetic progress for all important traits. These studies enabled the establishment of new genetic and genomic evaluation models, which are more efficient for selection to mastitis resistance. Further studies that are potential keys for future improvement of mastitis resistance are deep investigation of the bacteriology of mastitis, identification of novel indicator traits and tools for selection, and development of a larger female reference population to improve reliability of genomic evaluations. These cutting-edge studies will result in a better understanding of the genetic background of mastitis resistance and enable a more accurate phenotyping and genetic selection to improve mastitis resistance, and consequently, animal welfare and industry profitability.

Estimation of Genetic Parameters for Somatic Cell Scores of Holsteins Using Multi-trait Lactation Models in Korea.

The study was conducted to analyze the genetic parameters of somatic cell score (SCS) of Holstein cows, which is an important indicator to udder health. Test-day records of somatic cell counts (SCC) of 305-day lactation design from first to fifth lactations were collected on Holsteins in Korea during 2000 to 2012. Records of animals within 18 to 42 months, 30 to 54 months, 42 to 66 months, 54 to 78 months, and 66 to 90 months of age at the first, second, third, fourth and fifth parities were analyzed, respectively. Somatic cell scores were calculated, and adjusted for lactation production stages by Wilmink’s function. Lactation averages of SCS (LSCS1 through LSCS5) were derived by further adjustments of each test-day SCS for five age groups in particular lactations. Two datasets were prepared through restrictions on number of sires/herd and dams/herd, progenies/sire, and number of parities/cow to reduce data size and attain better relationships among animals. All LSCS traits were treated as individual trait and, analyzed through multiple-trait sire models and single trait animal models via VCE 6.0 software package. Herd-year was fitted as a random effect. Age at calving was regressed as a fixed covariate. The mean LSCS of five lactations were between 3.507 and 4.322 that corresponded to a SCC range between 71,000 and 125,000 cells/mL; with coefficient of variation from 28.2% to 29.9%. Heritability estimates from sire models were within the range of 0.10 to 0.16 for all LSCS. Heritability was the highest at lactation 2 from both datasets (0.14/0.16) and lowest at lactation 5 (0.11/0.10) using sire model. Heritabilities from single trait animal model analyses were slightly higher than sire models. Genetic correlations between LSCS traits were strong (0.62 to 0.99). Very strong associations (0.96 to 0.99) were present between successive records of later lactations. Phenotypic correlations were relatively weaker (<0.55). All correlations became weaker at distant lactations. The estimated breeding values (EBVs) of LSCS traits were somewhat similar over the years for a particular lactation, but increased with lactation number increment. The lowest EBV in first lactation indicated that selection for SCS (mastitis resistance) might be better with later lactation records. It is expected that results obtained from these multi-trait lactation model analyses, being the first large scale SCS data analysis in Korea, would create a good starting step for application of advanced statistical tools for future genomic studies focusing on selection for mastitis resistance in Holsteins of Korea.

Genetic selection for reduced somatic cell counts in sheep milk: A review

Mastitis is an inflammation of the udder, mainly caused by bacteria, and leads to economic loss, due to discarded milk, reduced milk production, reduced milk quality and increased health costs in both dairy sheep and cattle. Selecting for increased genetic resistance to mastitis can be done directly or indirectly, with the indirect selection corresponding to a prediction of the bacteriological status of the udder based on traits related to the infection. The most frequently used indirect method is currently milk somatic cell count (SCC) or somatic cell score (SCS). This review reports the state of the art relating to the genetic basis of mastitis resistance in sheep and explores the opportunities to use SCC as selection criterion in a breeding programme to improve resistance to mastitis in sheep, discussing the actual situation and prospects for improvement. It has been stressed, in particular, that although it is unlikely that selection for mastitis resistance by the farmers on their own will be successful, there is good prospect for genetic improvement if reliable pedigree and performance recording is implemented across flocks, combined with breeding value estimation. To achieve this, a strong and well-structured organization to implement and support the programme is essential.

Genetic parameters for test day somatic cell score in Brazilian Holstein cattle.

Selection for lower somatic cell count has been included in the breeding objectives of several countries in order to increase resistance to mastitis. Genetic parameters of somatic cell scores (SCS) were estimated from the first lactation test day records of Brazilian Holstein cows using random-regression models with Legendre polynomials (LP) of the order 3-5. Data consisted of 87,711 TD produced by 10,084 cows, sired by 619 bulls calved from 1993 to 2007. Heritability estimates varied from 0.06 to 0.14 and decreased from the beginning of the lactation up to 60 days in milk (DIM) and increased thereafter to the end of lactation. Genetic correlations between adjacent DIM were very high (>0.83) but decreased to negative values, obtained with LP of order four, between DIM in the extremes of lactation. Despite the favorable trend, genetic changes in SCS were not significant and did not differ among LP. There was little benefit of fitting an LP of an order >3 to model animal genetic and permanent environment effects for SCS. Estimates of variance components found in this study may be used for breeding value estimation for SCS and selection for mastitis resistance in Holstein cattle in Brazil.

Eight SNVs in NF-κB pathway genes and their different performances between subclinical mastitis and mixed Chinese Holstein cows

The nuclear factor-kappa B (NF-κB) pathway proteins are key players in controlling both innate and adaptive immunity. However, the information on NF-κB pathway genes is very limited in mastitis resistance and milk production of Chinese Holstein cows. In this study, we examine the association of the NF-κB pathway gene variants with milk quality traits and somatic cell score (SCS) in Chinese Holstein cows. Eight single nucleotide variants (SNVs) were identified within the bovine NF-κB pathway genes, using DNA pooled sequencing, PCR-RFLP, and forced PCR-RFLP methods. These SNVs include SNV1: g. 536 C>T (exon 10 of Rel), SNV2: g. 94 G>A (exon 20 of p100), SNV3: g. 43 T>C (intron 6 of p105), SNV4: g. 2397 T>G (intron 9 of p105), SNV5: g. 382 G>C (intron 1 of IκBδ), SNV6: g. 21 C>T (exon 5 of IκBζ), SNV7: g. 272 G>A (intron 6 of IκBζ), and SNV8: g. 18 C>T (intron 10 of IκBζ). The association analysis in mixed Chinese Holstein population showed that SNV1 was significantly or highly significantly associated (P<0.01 and P<0.05) with fat rate, protein rate and SCS. Furthermore, the SNV1-CC (wild genotype) determined serine showed the significantly lower SCS and higher milk production traits compared to TT and TC. SNV2 was significantly associated (P<0.05) with SCS; SNV3 was significantly associated (P<0.05) with fat rate; and SNV4 was significantly associated (P<0.05) with fat rate and SCS. In 199 subclinical mastitis Chinese Holstein cows, the statistical results absolutely differed from the mixed Chinese Holstein individuals. Splice-site prediction by SplicePort showed that single nucleotide difference at eight SNVs results in the acceptor score and donor score changing obviously that may lead to alternative splicing. In brief, SNV1, SNV2, SNV3 and SNV4 could be useful genetic markers for mastitis resistance selection and breeding in Chinese Holstein cows. Furthermore, whether these SNVs lead to alternative splicing need further research.

Association and Expression Analysis of Single Nucleotide Polymorphisms of Partial Tumor Necrosis Factor Alpha Gene with Mastitis in Crossbred Cattle

A total of 129 crossbred cows were selected to explore the genotypic and expression profiling of partial TNF-α gene and its association with mastitis susceptibility. Two exon spanning region of TNF-α gene (221 bp and 239 bp) were amplified by Polymerase Chain Reaction (PCR). The different genotypic analysis by SSCP revealed that 221 bp fragment was monomorphic, whereas 239 bp was polymorphic. Association studies revealed that AA genotypes of 239 bp were more prevalent in mastitis group and the mRNA expression of TNF-α was significantly (P < 0.05) higher in AA genotypic animals compare to AB and BB. This suggested that genotypes AB and BB may be used as candidate markers for mastitis resistance selection in dairy cattle.

Association of IL8 -105G/A with Mastitis Somatic Cell Score in Chinese Holstein Dairy Cows

The single nucleotide polymorphisms (SNPs) in the 5′ upstream of bovine IL8 gene were investigated in 810 Chinese Holstein cows from 35 bull families in a dairy farm in Shanghai using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) technique. The Real-time PCR and Western blot were used to detect the mRNA and protein levels of genotype Chinese Holstein dairy cows. The results showed that one SNP -105G>A was detected, designating three genotypes (GG, GA and AA) with respective frequencies of 0.38, 0.46, and 0.16. The significant association of the SNP -105G>A with somatic cell score (SCS) was identified. Genotype GG had a significantly lower SCS than genotype GA or AA (P < 0.01), and the relative mRNA expression and protein level of GG was found to be the highest. These results suggest that the genotype GG may be a useful genetic marker for mastitis resistance selection and breeding in Chinese Holstein dairy cows.

Association between lactoferrin single nucleotide polymorphisms and milk production traits in Polish Holstein cattle

Abstract. Bovine lactoferrin exhibits strong potential for further applications as a mastitis resistance marker. Since selection for mastitis resistance should not interfere with dairy performance, we investigated the association between bovine lactoferrin gene polymorphism and production traits in Polish Holsteins. The associations between four SNPs, localized in the 5’-flanking region and in exons 4 and 9 of the lactoferrin gene, and dairy performance were examined. SNPs were associated with almost all test-day milk performance traits. Significant associations were found between lactoferrin genotypes and the estimated breeding values for those traits. To find out whether the discrepancies between the lactoferrin gene SNP’s influence on phenotype (test-day milk performance) and on estimated breeding values originate from the impact of other factors, we explored the genotype by environment interaction. Substantial impacts of SCC, lactation stage and parity were found. This paper suggests that the genotype by environment interaction may significantly change associations between genes and traits. It is important to include similar analyses to the studies on disease markers before using them in the selection.

Polymorphism in PGLYRP-1 gene by PCR-RFLP and its association with somatic cell score in Chinese Holstein

Bovine peptidoglycan recognition protein 1 (PGLYRP-1), an important pattern recognition molecule (PRM) of the innate immune system, is an effector molecule in killing different microorganisms directly. To investigate whether the PGLYRP-1 gene was associated with mastitis and milk production traits in dairy cattle, the polymorphism of this gene was analyzed by PCR-RFLP in a population of 524 Chinese Holstein. A total of ten single nucleotide polymorphism (SNP) loci were identified. The association analysis of single SNP locus showed that T−35A, T−12G and G+102C were significantly associated (P<0.05) with somatic cell score (SCS), while G+102C and G+649C were significantly associated (P<0.05) with 305-day milk yield. Association analysis between combined haplotypes and SCS, milk production traits indicated that H3H3 was associated with the lower SCS (P<0.01), and H2H2 was associated with the lower 305-day milk yield (P<0.01). These findings demonstrated that polymorphisms in PGLYRP-1 gene associated with mastitis resistance and 305-day milk yield, and the H3H3 would provide a useful genetic marker of combined haplotypes for mastitis resistance selection and breeding in Chinese Holstein.

Confirmation and fine‐mapping of clinical mastitis and somatic cell score QTL in Nordic Holstein cattle

A genome-wide association study of 2098 progeny-tested Nordic Holstein bulls genotyped for 36387 SNPs on 29 autosomes was conducted to confirm and fine-map quantitative trait loci (QTL) for mastitis traits identified earlier using linkage analysis with sparse microsatellite markers in the same population. We used linear mixed model analysis where a polygenic genetic effect was fitted as a random effect and single SNPs were successively included as fixed effects in the model. We detected 143 SNP-by-trait significant associations (P<0.0001) on 20 chromosomes affecting mastitis-related traits. Among them, 21 SNP-by-trait combinations exceeded the genome-wide significant threshold. For 12 chromosomes, both the present association study and the previous linkage study detected QTL, and of these, six were in the same chromosomal locations. Strong associations of SNPs with mastitis traits were observed on bovine autosomes 6, 13, 14 and 20. Possible candidate genes for these QTL were identified. Identification of SNPs in linkage disequilibrium with QTL will enable marker-based selection for mastitis resistance. The candidate genes identified should be further studied to detect candidate polymorphisms underlying these QTL.

The influence of genetic selection on mastitis resistance

As milk yields and herd sizes continue to rise, a greater emphasis is likely to be placed on selection for health and fitness traits against production traits. The purpose of this article is to discuss the current selection tools available to producers for selection for mastitis resistance and highlight areas of new and emerging technologies which will undoubtedly contribute in the future.