Genome wide scan for somatic cell counts in holstein bulls

An alternative experimental case-control design for genetic association studies on bovine mastitis

The possibility of using genetic control strategies to increase disease resistance to infectious diseases relies on the identification of markers to include in the breeding plans. Possible incomplete exposure of mastitis-free (control) animals, however, is a major issue to find relevant markers in genetic association studies for infectious diseases. Usually, designs based on elite dairy sires are used in association studies, but an epidemiological case-control strategy, based on cows repeatedly field-tested could be an alternative for disease traits. To test this hypothesis, genetic association results obtained in the present work from a cohort of Italian Holstein cows tested for mastitis over time were compared with those from a previous genome-wide scan on Italian Holstein sires genotyped with 50k single nucleotide polymorphisms for de-regressed estimated breeding values for somatic cell counts (SCCs) on Bos taurus autosome (BTA6) and BTA14. A total of 1121 cows were selected for the case-control approach (cases=550, controls=571), on a combination of herd level of SCC incidence and of within herd individual level of SCC. The association study was conducted on nine previously identified markers, six on BTA6 and four on BTA14, using the R statistical environment with the 'qtscore' function of the GenABEL package, on high/low adjusted linear score as a binomial trait. The results obtained in the cow cohort selected on epidemiological information were in agreement with those obtained from the previous sire genome-wide association study (GWAS). Six out of the nine markers showed significant association, four on BTA14 (rs109146371, rs109234250, rs109421300, rs109162116) and two on BTA6 (rs110527224 and rs42766480). Most importantly, using mastitis as a case study, the current work further validated the alternative use of historical field disease data in case-control designs for genetic analysis of infectious diseases in livestock.

Bovine mastitis: frontiers in immunogenetics

Mastitis is one of the most prevalent and costly diseases in the dairy industry with losses attributable to reduced milk production, discarded milk, early culling, veterinary services, and labor costs. Typically, mastitis is an inflammation of the mammary gland most often, but not limited to, bacterial infection, and is characterized by the movement of leukocytes and serum proteins from the blood to the site of infection. It contributes to compromised milk quality and the potential spread of antimicrobial resistance if antibiotic treatment is not astutely applied. Despite the implementation of management practises and genetic selection approaches, bovine mastitis control continues to be inadequate. However, some novel genetic strategies have recently been demonstrated to reduce mastitis incidence by taking advantage of a cow's natural ability to make appropriate immune responses against invading pathogens. Specifically, dairy cattle with enhanced and balanced immune responses have a lower occurrence of disease, including mastitis, and they can be identified and selected for using the high immune response (HIR) technology. Enhanced immune responsiveness is also associated with improved response to vaccination, increased milk, and colostrum quality. Since immunity is an important fitness trait, beneficial associations with longevity and reproduction are also often noted. This review highlights the genetic regulation of the bovine immune system and its vital contributions to disease resistance. Genetic selection approaches currently used in the dairy industry to reduce the incidence of disease are reviewed, including the HIR technology, genomics to improve disease resistance or immune response, as well as the Immunity(+)™ sire line. Improving the overall immune responsiveness of cattle is expected to provide superior disease resistance, increasing animal welfare and food quality while maintaining favorable production levels to feed a growing population.

A SNP in intron 8 of CD46 causes a novel transcript associated with mastitis in Holsteins

Background

The membrane protein CD46, a ubiquitous cell surface pathogen receptor, can bind Streptococcus to trigger cell autophagy, which is a critical step in the control of infection.

Results

In this study, we found a new splice variant designated CD46 transcript variant (CD46-TV). The splice variant is characterized by the retention of a 48 bp sequence from intron 8 of the bovine CD46 gene, which encodes a putative protein enlarged by 16 amino acids. CD46-TV mRNA was found to be over expressed in mastitis-infected mammary gland tissues relative to healthy tissues. A single nucleotide polymorphism (c. 1033 + 2184 C > T) in the exonic splicing enhancer (ESE) motif region was shown to result in the CD46-TV aberrant splice variant through constructing alternative alleles using the pSPL3 exon capturing vector and transfecting these into 293 T cells. Allelic frequency in 56,682 individuals belonging to 112 Bos taurus, Bos indicus, Bos javanicus, Bos grunniens and Bos mutus, etc. suggests that the C allele (80.09%) is the ancestral allele. Association analysis found that the mean genomic estimated breeding values (gEBV) for milk somatic cell score and the occurrence of clinical mastitis, as well as the milk somatic cell score of Chinese Holsteins with the CT genotype was lower than those of individuals with either the CC or TT genotypes. The mean gEBV for udder health synthesis for the TT genotype was greater than those for the CC or CT genotypes.

Conclusions

Our findings suggest that the CD46 gene likely plays a critical role in the risk of mastitis caused by Streptococcus in dairy cows via an alternative splicing mechanism caused by a functional mutation in intron 8. Our data also underline the importance of variation within ESEs in regulating transcript processing.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-630) contains supplementary material, which is available to authorized users.

Prevalence of sub-clinical mastitis in dairy farms

A total of 560 lactating cows belonging to Bangladesh Agricultural University dairy farm (n = 59): Local Zebu (L), Local × Friesian (L × F), Local × Jersey (L × J), Local × Red Chittagong Cattle (L × RCC), Local × Sahiwal (L × SL), Red Chittagong Cattle (RCC); and Central Cattle Breeding Station and Dairy Farm (n = 501): Local Zebu, L × F, SL × F, Sahiwal and Australian Friesian Sahiwal (AFS) were selected to measure prevalence of subclinical mastitis (SM). The California Mastitis Test was done and the prevalence of SM was 68% on cow basis and 57% on quarter basis. The prevalence rate was significantly higher in L × F (87%, P < 0.05), SL × F (88%, P < 0.05), L × J (100%, P < 0.01), AFS (89%, P< 0.05) and SL (100%, P < 0.01). The local Zebu (31%) and RCC (28%) were least susceptible to SM. SM was significantly higher in multiparous (P < 0.05) and older cows (P < 0.05). The front quarters were more prone to SM than the rear. Factors such as breed, age, parity and management may have been responsible for high prevalence of SM in both farms. DOI: http://dx.doi.org/10.3329/bvet.v30i2.18257 Bangl. vet. 2013. Vol. 30, No. 2, 70-77

The mammary gland in domestic ruminants: a systems biology perspective

Milk and dairy products are central elements in the human diet. It is estimated that 108kg of milk per year are consumed per person worldwide. Therefore, dairy production represents a relevant fraction of the economies of many countries, being cattle, sheep, goat, water buffalo, and other ruminants the main species used worldwide. An adequate management of dairy farming cannot be achieved without the knowledge on the biological mechanisms behind lactation in ruminants. Thus, understanding the morphology, development and regulation of the mammary gland in health, disease and production is crucial. Presently, innovative and high-throughput technologies such as genomics, transcriptomics, proteomics and metabolomics allow a much broader and detailed knowledge on such issues. Additionally, the application of a systems biology approach to animal science is vastly growing, as new advances in one field of specialization or animal species lead to new lines of research in other areas or/and are expanded to other species. This article addresses how modern research approaches may help us understand long-known issues in mammary development, lactation biology and dairy production.

BIOLOGICAL SIGNIFICANCE

Dairy production depends upon the knowledge of the morphology and regulation of the mammary gland and lactation. High-throughput technologies allow a much broader and detailed knowledge on the biology of the mammary gland. This paper reviews the major contributions that genomics, transcriptomics, metabolomics and proteomics approaches have provided to understand the regulation of the mammary gland in health, disease and production. In the context of mammary gland "omics"-based research, the integration of results using a Systems Biology Approach is of key importance.