Intramammary infections in primiparous Holsteins: heritabilities and comparisons of bovine leukocyte adhesion deficiency carriers and noncarriers

Genetic analysis of pathogen-specific intramammary infections in dairy cows

Mastitis is one of the most common diseases in dairy cattle, causing severe economic losses to dairy farmers. Mastitis usually occurs due to intramammary infection (IMI) caused by a variety of pathogenic bacteria. Although good progress has been made in understanding genetics of pathogen-specific clinical mastitis, studies involving genetic analysis of pathogen-specific IMI are scarce. The overall objective of this study was, therefore, to assess genetic variation of overall and pathogen-specific IMI in nonclinical primiparous and multiparous cows using bacterial culture. Data and milk samples were collected over a 2-yr interval as part of the Canadian Bovine Mastitis Research Network. The final data set contained records of 46,900 quarter milk samples from 3,382 clinically healthy primiparous and multiparous Holstein cows from 84 dairy herds. For the genetic analysis, we considered the following 7 traits: overall IMI, non-aureus staphylococci (NAS) IMI, contagious pathogen IMI, environmental pathogen IMI, major pathogen IMI, minor pathogen IMI and somatic cell score (SCS). Data were analyzed at the quarter level using a threshold-probit model via Gibbs sampling in BLUPF90. Prevalence of IMI traits at the quarter level in multiparous cow from 0 to 400 DIM ranged from 6.8 to 45.5%. Posterior mean of quarter heritability estimates (on the underlying scale, posterior SD in brackets) of overall IMI and pathogen-specific IMI traits ranged from 0.017 to 0.073 (±0.009 to 0.030). Weak to strong genetic correlations [ranging from 0.18 to 0.97 (±0.01 to 0.29)] among pathogen-specific IMI traits and with overall IMI indicated that not all of these traits were genetically similar. Weak to moderate Spearman rank correlations between estimated breeding values for overall IMI and pathogen-specific IMI traits (from 0.31 to 0.87) indicated possible substantial reranking of sires. The percentage of daughters with IMI caused by various pathogen groups ranged from 13 to 80% and from 38 to 94% for the best (10% decile) and worst sires (90% decile) according to their IMI trait-specific estimated breeding values, respectively. Pathogen-specific IMI traits and overall IMI had weak to moderate positive genetic correlations [ranging from 0.11 to 0.81 (±0.11 to 0.22)] with SCS. Therefore, selection for lower SCS will improve resistance to IMI. However, based on the observed weak to moderate rank correlations (0.04 to 0.47) between pathogen-specific IMI traits and SCS, selection for lower SCC will not improve resistance to IMI from every pathogen-specific IMI group in the same manner. Therefore, despite low heritability estimates, there was sizeable genetic variation for pathogen-specific IMI traits, indicating that long-term direct genetic selection for pathogen-specific IMI can improve pathogen-specific IMI resistance.

Pathogen-group specific association between CXCR1 polymorphisms and subclinical mastitis in dairy heifers

The chemokine (C-X-C motif) receptor 1 (CXCR1) gene encodes the homonymous receptor for interleukin 8 (IL8) on polymorphonuclear neutrophilic leucocytes (PMNL). Binding causes migration from blood to milk, activation and prolonged survival of PMNL, a crucial process in the innate immune defence of the bovine mammary gland against invading mastitis-causing pathogens. The main objective of this study was to screen the entire coding region of the CXCR1 gene for polymorphisms and to analyse their association with udder health of dairy heifers. One-hundred-and-forty Belgian Holstein heifers originating from 20 commercial dairy farms were genotyped by DNA sequencing. Detailed phenotypic data on udder health was available including quarter bacteriological culture results and somatic cell count (SCC) in early lactation and composite milk SCC during first lactation. In total, 16 polymorphisms (including 8 missense mutations) were detected. Polymorphism c.980A>G was associated with pathogen-group specific IMI: heifers with genotype AG were less likely to have an IMI due to major mastitis pathogens compared with heifers with genotype GG but did not have less IMI by coagulase-negative staphylococci, so-called minor pathogens. CXCR1 genotype was neither associated with quarter SCC in early lactation nor with composite SCC during lactation. Although mastitis susceptibility is influenced by many factors, some genetic polymorphisms potentially have major effects on udder health of heifers, as was shown here. These results trigger us to further study the relationship between CXCR1 polymorphisms and mastitis susceptibility in both observational and experimental trials.

Screening for bovine leukocyte adhesion deficiency, deficiency of uridine monophosphate synthase, complex vertebral malformation, bovine citrullinaemia, and factor XI deficiency in Holstein cows reared in Turkey

Background

Bovine leukocyte adhesion deficiency (BLAD), deficiency of uridine monophosphate synthase (DUMPS), complex vertebral malformation (CVM), bovine citrullinaemia (BC) and factor XI deficiency (FXID) are autosomal recessive hereditary disorders, which have had significant economic impact on dairy cattle breeding worldwide. In this study, 350 Holstein cows reared in Turkey were screened for BLAD, DUMPS, CVM, BC and FXID genotypes to obtain an indication on the importance of these defects in Turkish Holsteins.

Methods

Genomic DNA was obtained from blood and the amplicons of BLAD, DUMPS, CVM, BC and FXID were obtained by using PCR. PCR products were digested with TaqI, AvaI and AvaII restriction enzymes for BLAD, DUMPS, and BC, respectively. These digested products and PCR product of FXID were analyzed by agarose gel electrophoresis stained with ethidium bromide. CVM genotypes were detected by DNA sequencing. Additionally, all genotypes were confirmed by DNA sequencing to determine whether there was a mutant allele or not.

Results

Fourteen BLAD, twelve CVM and four FXID carriers were found among the 350 Holstein cows examined, while carriers of DUMPS and BC were not detected. The mutant allele frequencies were calculated as 0.02, 0.017, and 0.006 for BLAD, CVM and FXID, respectively with corresponding carrier prevalence of 4.0% (BLAD), 3.4% (CVM) and 1.2% (FXID).

Conclusion

This study demonstrates that carriers of BLAD, CVM and FXID are present in the Turkish Holstein population, although at a low frequency. The actual number of clinical cases is unknown, but sporadic cases may appear. As artificial insemination is widely used in dairy cattle breeding, carriers of BLAD, CVM and FXID are likely present within the population of breeding sires. It is recommended to screen breeding sires for these defective genes in order to avoid an unwanted spread within the population.

Genetic parameters for somatic cell score according to udder infection status in Valle del Belice dairy sheep and impact of imperfect diagnosis of infection

Background

Somatic cell score (SCS) has been promoted as a selection criterion to improve mastitis resistance. However, SCS from healthy and infected animals may be considered as separate traits. Moreover, imperfect sensitivity and specificity could influence animals' classification and impact on estimated variance components. This study was aimed at: (1) estimating the heritability of bacteria negative SCS, bacteria positive SCS, and infection status, (2) estimating phenotypic and genetic correlations between bacteria negative and bacteria positive SCS, and the genetic correlation between bacteria negative SCS and infection status, and (3) evaluating the impact of imperfect diagnosis of infection on variance component estimates.

Methods

Data on SCS and udder infection status for 1,120 ewes were collected from four Valle del Belice flocks. The pedigree file included 1,603 animals. The SCS dataset was split according to whether animals were infected or not at the time of sampling. A repeatability test-day animal model was used to estimate genetic parameters for SCS traits and the heritability of infection status. The genetic correlation between bacteria negative SCS and infection status was estimated using an MCMC threshold model, implemented by Gibbs Sampling.

Results

The heritability was 0.10 for bacteria negative SCS, 0.03 for bacteria positive SCS, and 0.09 for infection status, on the liability scale. The genetic correlation between bacteria negative and bacteria positive SCS was 0.62, suggesting that they may be genetically different traits. The genetic correlation between bacteria negative SCS and infection status was 0.51. We demonstrate that imperfect diagnosis of infection leads to underestimation of differences between bacteria negative and bacteria positive SCS, and we derive formulae to predict impacts on estimated genetic parameters.

Conclusions

The results suggest that bacteria negative and bacteria positive SCS are genetically different traits. A positive genetic correlation between bacteria negative SCS and liability to infection was found, suggesting that the approach of selecting animals for decreased SCS should help to reduce mastitis prevalence. However, the results show that imperfect diagnosis of infection has an impact on estimated genetic parameters, which may reduce the efficiency of selection strategies aiming at distinguishing between bacteria negative and bacteria positive SCS.

Mathematical model of the acute inflammatory response to Escherichia coli in intramammary challenge

We constructed a mathematical model of the early response to Escherichia coli infection of the mammary gland and explored the roles and interactions between inflammatory cells and bacteria. The model incorporates 3 equations that describe the interactions among bacteria, milk somatic cells, and blood leukocyte densities. These 3 equations were fitted to cell densities observed during acute inflammatory responses in unvaccinated and vaccinated heifers inoculated with 10(4) or 10(6) cfu of E. coli. The rates computed for the cellular transit from the storage sites to the blood and from the blood to the milk were lower in cows receiving 10(4) cfu but increased at approximately 6 x 10(-6) and 30 x 10(-6) microL/cfu per h in nonvaccinated or vaccinated cows inoculated with 10(6) cfu, respectively. The cellular rates of bacterial killing were highest in unvaccinated cows ( approximately 400 x 10(-6) microL/cell per h) when compared with vaccinated cows (200 to 300 x 10(-6) microL/cell per h). A critical density of milk somatic cells at which bacteria density is constant was computed from the model at 2 x 10(6) cells/mL, and a one-way sensitivity analysis revealed that the changes in milk cellular densities were mostly sensitive to variations in the rate of bacterial killing and in the rate of production of inflammatory cells.

Bovine Leukocyte Adhesion Deficiency (BLAD): A Review

Bovine leukocyte adhesion deficiency (BLAD) in Holstein cattle is an autosomal recessive congenital disease characterized by recurrent bacterial infections, delayed wound healing and stunted growth, and is also associated with persistent marked neutrophilia. The molecular basis of BLAD is a single point mutation (adenine to guanine) at position 383 of the CD18 gene, which caused an aspartic acid to glycine substitution at amino acid 128 (D128G) in the adhesion molecule CD18. Neutrophils from BLAD cattle have impaired expression of the beta2 integrin (CD11a,b,c/CD18) of the leukocyte adhesion molecule. Abnormalities in a wide spectrum of adherence dependent functions of leukocytes have been fully characterized. Cattle affected with BLAD have severe ulcers on oral mucous membranes, severe periodontitis, loss of teeth, chronic pneumonia and recurrent or chronic diarrhea. Affected cattle die at an early age due to the infectious complications. Holstein bulls, including carrier sires that had a mutant BLAD gene in heterozygote were controlled from dairy cattle for a decade. The control of BLAD in Holstein cattle by publishing the genotypes and avoiding the mating between BLAD carriers was found to be successful. This paper provides an overview of the genetic disease BLAD with reference to the disease in Holstein cattle.

Genetic factors affecting susceptibility of dairy cows to udder pathogens

Bovine mastitis remains the most costly disease in dairy cattle. Breeding for resistance to udder pathogens has been proposed as a complementary tool to therapeutic and prophylactic measures not totally effective against the disease. This paper reviews factors affecting cows' susceptibility to pathogens at the animal, cellular/hormonal and DNA levels. Such factors will be useful in achieving genetic improvement for resistance only if they have desirable properties at the genetic and immunological levels. Because such properties are not always of significant magnitude, further research is necessary to identify characteristics of resistance in cows, considering the constant and complex interactions that occur between hosts and pathogens.

Relationships among severity and duration of clinical mastitis and sire transmitting abilities for somatic cell score, udder type traits, productive life, and protein yield

The objective of this study was to determine the relationships among severity and duration of clinical mastitis during first and second lactation and sire transmitting abilities for somatic cell score, udder type traits, productive life, and protein yield. Recording of clinical episodes began at first parturition for 1704 Holstein cows (in six Pennsylvania herds and one Nebraska herd) and continued into second lactation for 1055 of these cows. A total of 456 cows (sired by 168 bulls) had at least one clinical episode during first lactation, and 230 cows (sired by 100 bulls) had at least one clinical episode during second lactation. A severity code from 1 (normal milk) to 5 (acute systemic mastitis) was assigned daily (for up to 30 d after detection) to all quarters that had clinical mastitis. Only the severity codes for the first clinical episode to occur during first and second lactation are considered here. The initial and maximum severity codes, as well as the natural logarithms of both the sum of severity codes that were above normal (> 1) and the total days severity codes were above normal were regressed on herd (a classification variable), age at first calving, days in milk at clinical detection, and sire transmitting abilities taken one at a time. Linear and nonlinear effects were estimated for sire transmitting abilities. Separate analyses were conducted on dependent variables that considered severity and duration of clinical mastitis from: all organisms, coagulase-negative staphylococci, coliform species, streptococci other than Streptococcus agalactiae, and the most common environmental organisms (coliform species and streptococci other than Streptococcus agalactiae). Daughters of sires that transmit the lowest somatic cell score had the least severe and shortest clinical episodes from environmental organisms during first lactation. Selection for lower somatic cell score may reduce the severity and duration of clinical episodes from environmental organisms during first lactation.

Mammary gland immunology around parturition. Influence of stress, nutrition and genetics

Adequate immune functions are essential for the defence against udder infections. Detailed knowledge about the immune response and important defence factors is essential in order to find new ways for the prevention and treatment of udder infections leading to mastitis. Work should be concentrated on ways of minimising the negative influence on immune functions and/or ways of stimulating these functions, especially during periods of immune suppression. A depression of important immune functions has been reported around parturition and there is a higher prevalence of clinical mastitis and other diseases during this period. Immunosuppression is often associated with high levels of glucocorticoids in blood, a common finding around parturition and during stressful conditions. A number of stressors are present around calving, e.g. parturition, onset of lactation and changes in feeding and management regimes. Adequate management including feeding strategies and routines are important for the immune functions. Metabolic stress as well as deficiencies in vitamins and minerals around parturition and during the first month of lactation can have a negative influence on the immune functions and thereby increase the risks for udder infections and mastitis. There seem to be a genetic variability in certain immune functions among periparturient cows. This might indicate a possibility to find markers for genetic selection of individuals with a well-developed immune system without negative effects on milk productivity.

Clinical mastitis in primiparous Holsteins: comparisons of bovine leukocyte adhesion deficiency carriers and noncarriers

The objective of this study was to determine the impact of bovine leukocyte adhesion deficiency on clinical mastitis incidence, severity, and duration in Holstein cows. Genomic DNA from milk of 847 Holstein cows in six Pennsylvania herds was used to determine bovine leukocyte adhesion deficiency genotypes (82 or 9.7% carriers). Data on clinical mastitis incidence, severity, duration, and pathogen involved were collected during first lactation for the project cows. One hundred ninety-four cows had one or more clinical mastitis episodes; milk samples from each quarter with clinical mastitis were collected at discovery of the episode and were cultured following National Mastitis Council recommendations. The overall incidence of clinical mastitis was significantly affected by sire and herd-year-season of calving. In addition, incidence of clinical mastitis tended to increase with age at first calving. Severity and duration of clinical mastitis were impacted by the pathogen involved. Incidence of clinical mastitis from all pathogens, from coagulase-negative staphylococci, and from coliform bacteria was not significantly related to bovine leukocyte adhesion deficiency status. Carriers tended to have lower rates of mastitis from streptococci other than Streptococcus agalactiae when compared with noncarriers, but this result should be interpreted with caution because of the low frequency of mastitis from the streptococci. Bovine leukocyte adhesion deficiency status was unrelated to severity or duration of clinical episodes. Bovine leukocyte adhesion deficiency carriers are probably similar to noncarriers in resistance to clinical mastitis.