Bonnie A. Mallard

Selection for high immune response: an alternative approach to animal health maintenance?

To test the hypothesis that variation in ability to respond immunologically correlates with health, Yorkshire pigs were bred for high (HIR) and low (LIR) antibody (Ab) and cell-mediated immune response (CMI). Selection was based on standardized measures of Ab (secondary response to hen egg white lysozyme, serum IgG concentration) and CMI (cutaneous delayed-type hypersenstivity to purified protein derivative of tuberculin after immunization with bacillus Calmette-Guérin and in vitro lymphocyte response to Con-A). Differences in Ab and CMI by line were not restricted to the antigens used in the selection. Antibody response to vaccines was highest in HIR and non-responders were restricted to LIR pigs. The HIR pigs had the best rate of weight gain. After infection with Mycoplasma hyorhinis, HIR developed more severe arthritis and less polyserositis. Differences were associated with variation in cytokine message in joint-related cells. Following exposure to attenuated transmissible gastroenteritis virus, natural killer cells of the LIR pigs but not of HIR or control lines, were unresponsive. Genetic selection for Ab and CMI may provide health and productivity advantages and complement traditional health-maintenance methods.

Use of estimated breeding values in a selection index to breed Yorkshire pigs for high and low immune and innate resistance factors

Abstract A random bred population of Yorkshire pigs (Go) was characterized using fourteen various indicators of immune and innate resistance. Based on initial heritability estimates and correlations between these traits, two measures of antibody (serum IgG, and antibody response to HEWL), and cellular activity (blastogenic response to Con A and cutaneous DTH to BCG/PPD), and one indicator of innate monocyte function (uptake and killing of S. typhimurium) were chosen as breeding criteria to be used in a composite selection index. Based on these five traits a combined estimated breeding value (EBV) was calculated for each animal and pigs were assigned to High, Low or Control breeding groups. Approximately 120 first generation piglets (G1) were then similarly evaluated. Based on Go plus G1 heritability estimates were 0.25, 0.23, 0.08, 0.08 and zero for secondary antibody response to HEWL, blastogenic response to Con A, cutaneous DTH to BCG/PPD, serum IgG, and monocyte function, respectively. Least squares me...

EFFECTS OF PERIPARTUM STRESS AND HEALTH ON CIRCULATING BOVINE LYMPHOCYTE SUBSETS

Alterations in the proportions of peripheral blood lymphocyte subsets was monitored using flow cytometry, before, during and after the peripartum period (week-8 to week (wk) 16) of dairy cows, when pregnancy and lactational stresses prevail and disease incidence is highest. A health code was assigned to each animal at each sampling time, and a subset of non-pregnant, non-lactating (NPNL) cows were sampled for comparisons, and to examine the effect of pregnancy and lactation only, on lymphocyte subset proportions. Results were expressed as the percentage of positive stained cells expressing CD2, CD4, CD8, WC1(gamma delta), IgM and class II major histocompatibility complex (MHC-II) molecules, as determined by flow cytometry. Comparisons of subset proportions were made across time and between health status categories. Mean fluorescence intensity (MFI) values were also examined across the periparturient period for CD2, CD4, CD8 and gamma delta T cell subsets. All T cell subsets varied significantly during the perparturient period in healthy cows, especially around parturition. B cell and MHC-II+ populations remained relatively constant until after calving and then significantly (P < or = 0.06) decreased. Compared to NPNL cows, all T cell subsets were significantly lower in healthy cows at most time points, whereas B cell and MHC-II+ cells were comparable to the NPNL values. CD2, CD4, and CD8 subsets decreased significantly at wk-3 and returned to initial subset proportions by wk 16. Conversely, the WC1 population increased at wk-3 relative to calving but declined to approximate initial proportions at calving. Health status had no significant overall effect on any subset unless it was separated by weeks in which case there were interactions between health and week for CD2 and CD8. Results indicate that variations in T lymphocyte subsets and in the concentrations of surface marker molecules (MFI) occur more as a result of pregnancy and lactation than health status in the dairy cow and that these factors have the least influence upon B cell and MHC-II+ populations during the periparturient period.

Effects of growth hormone, insulin-like growth factor-I, and cortisol on periparturient antibody response profiles of dairy cattle

The objectives of this study were to determine hormone and antibody response profiles from the prepartum period to peak lactation, and evaluate potential immunomodulatory effects of the classic endocrine hormones, growth hormone (GH), insulin-like growth factor-I (IGF-I) and cortisol. Specifically, 33 Holstein cows were immunized with ovalbumin (OVA) and Escherichia coli J5 at weeks -8 and -3 prior to parturition. At parturition (week 0), cows received an additional immunization of OVA. Blood was collected at weeks -8, -3, 0, 3 and 6 relative to parturition and various samples were used to determine plasma hormone concentration, serum immunoglobulin (Ig), and specific antibody response to OVA and E. coli. Colostrum and milk samples were also collected post-parturition to monitor local immunoglobulin and antibody responses. Results indicated that not all periparturient cows exhibited depressed immune response, and that antibody response to OVA could be used to partition cows into 3 groups recognizing animals with sustained measurable antibody response before and after parturition (Group 1), animals which responded poorly to immunization at parturition (Group 2), and animals which did not respond to immunizations at week -3 or parturition (Group 3). Cows with the highest antibody response to OVA (Group 1) also tended (P < or = 0.10) to have the highest response to E. coli J5 at parturition and had the lowest incidence of disease, particularly mastitis. Antibody response to OVA measured in milk tended to be higher in Group 1 cows, particularly at week 0 (P < or = 0.06) compared to cows of Group 3. IGF-I was higher (P < or = 0.05) in cows of Group 1 than Group 3 at peak lactation (week 6).

Effects of chromium on health status, blood neutrophil phagocytosis and in vitro lymphocyte blastogenesis of dairy cows.

The objective of this study was to determine the effects of supplemental dietary chromium (Cr) on health status and mastitis-related parameters, as well as neutrophil phagocytic activity of dairy cows during late pregnancy and early lactation. In addition, possible interactions and involvements of Cr with insulin, cortisol, somatotropin (rBST) and insulin-like growth factor-1 (IGF-1) were directly investigated in vitro based on blastogenic responses using peripheral blood lymphocytes (PBL) of eight cows fed the control diet. Forty pregnant Holsteins, 18 primiparous and 22 multiparous, at week (wk) 6 before the expected calving dates were randomly assigned to treatments: control and supplemental chelated Cr (0.5 ppm) in the diet. All cows were managed in a normal production operation and health status was assessed by recording the incidence of health problems during the experimental period of wks 6 before and 16 after calving (-6 to 16 wks). Mastitis-related parameters included somatic cell counts (SCC), bacterial colony counts of milk samples from each mammary gland quarter of all cows during wk 1 to wk 8 postpartum. Peripheral blood neutrophil phagocytic function of eight cows fed either control or supplemental Cr diet was determined by the ability to take up uniform fluorescent beads measured by flow cytometry. Supplemental Cr had no effect (P > 0.10) on health status of cows during late pregnancy and early lactation, or on SCC and bacterial colonies of quarter milk samples from early lactation (wks 1 to 8). Supplemental Cr also did not affect neutrophil phagocytic function of cows from 6 wks prepartum to 6 wks postpartum. However, in the in vitro study of PBL (from control animals, not fed Cr diet) blastogenesis with addition of insulin or cortisol at two levels (0.05 and 0.5 ng ml-1), insulin and cortisol enhanced or had no effect on PBL proliferations with or without concanavalin A (con A) simulation. However, further Cr addition in the culture medium containing supplemental insulin or cortisol, particularly CrCl3, additively increased (P < 0.05) BPL blastogenic activities with or without con a stimulation. Conversely, addition of rBST or IFG-1 (0.5 and 5.0 ng ml-1) in the culture medium enhanced PBL proliferation, but addition of Cr gave no additional effect. These results indicated that supplemental Cr had no beneficial effect on health status, mastitis-related parameters or neutrophil phagocytic activity of dairy cows. However, in vitro study confirmed and extended our previous observations that Cr has an effect on lymphocyte proliferation and this may associate with insulin or cortisol actions.

Presence of glutamine at position 74 of pocket 4 in the BoLA-DR antigen binding groove is associated with occurrence of clinical mastitis caused by Staphylococcus species

Potential relationships between amino acid motifs in the antigen binding groove of various alleles of the bovine major histocompatibility complex DR (BoLA-DR) molecule and occurrence of clinical mastitis caused by Staphylococcus species (non-Staphylococcus aureus) were investigated in a case-control study. A significant association (P< or =0.05) was detected between the presence of glutamic acid at position beta 74 and occurrence of mastitis caused by Staphylococcus spp. with a relative risk of 11. This motif is present in BoLA-DRB3.2*22, *23 and *24 alleles. Presence of a positively charged residue (arginine or lysine) at position 13 also showed a tendency (P< o r=0.1) towards an association with a higher risk of clinical mastitis caused by the same bacteria. This motif is present in BoLA-DRB3.2*23 and *8 alleles. Similarly, presence of arginine at position beta 71 (present in alleles *23 and *22) was associated with occurrence of this disease. These positions (beta 13, beta 71 and beta 74) form pocket 4 of the antigen binding groove, which plays an instrumental role in antigen binding and recognition by T-lymphocytes. Thus, it can be concluded that pocket 4 of the BoLA-DR molecule is involved in conferring susceptibility to clinical mastitis caused by Staphylococcus spp.

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.

Genetic parameters of adaptive immune response traits in Canadian Holsteins

The objectives of this study were to estimate genetic parameters of cell-mediated (CMIR) and antibody-mediated (AMIR) immune response (IR) traits of Holstein cattle on a national scale and to associate estimated breeding values of CMIR, AMIR, and overall IR with routinely evaluated traits in Canada. In collaboration with the Canadian Bovine Mastitis Research Network, 445 Holstein cows from 42 herds across Canada were immunized to measure delayed-type hypersensitivity as an indicator of CMIR and serum antibody for AMIR to putative type 1 and type 2 test antigens, respectively. Primary (d 14) and secondary (d 21) AMIR were measured for both IgG1 and IgG2. A series of uni- and bivariate linear animal models were used to estimate genetic parameters and breeding values for CMIR and the 4 AMIR traits. The models included the fixed effects of parity and stage of lactation and the random effects of herd-technician, animal, and residual. Heritability of CMIR was 0.19 (SE=0.10) and for AMIR traits ranged from 0.16 to 0.41 (SE=0.09-0.11) depending on time and antibody isotype. The genetic correlations between CMIR and AMIR were negative and ranged from -0.13 to -0.45 (SE=0.32-0.46). The results indicate adaptive immune response traits are moderately heritable and provide a potential for genetic selection. The negative genetic correlations between CMIR and AMIR indicate the importance of considering both traits in breeding for overall disease resistance. Significant beneficial associations between the reproductive traits number of services and first service to conception were found, which may indicate these reproductive traits would improve with genetic selection for enhanced immune response.

Short communication: Association of disease incidence and adaptive immune response in Holstein dairy cows

The objective of this study was to use previously calculated estimated breeding values for cell- (CMIR) and antibody-mediated immune responses (AMIR) to determine associations between immune response (IR) and economically important diseases of dairy cattle. In total, 699 Holsteins were classified as high, average, or low for CMIR, AMIR, and overall IR (combined CMIR and AMIR), and associations with mastitis, metritis, ketosis, displaced abomasums, and retained fetal membranes were determined. The incidence of mastitis was higher among average cows as compared with cows classified as high AMIR [odds ratio (OR)=2.5], high CMIR (OR=1.8), or high IR (OR=1.8). Low-CMIR cows had a higher incidence of metritis (OR=11.3) and low-IR cows had a higher incidence of displaced abomasum (OR=4.1) and retained fetal membrane (OR=2.8) than did average responders. Results of this study show that cows classified as high immune responders have lower occurrence of disease, suggesting that breeding cattle for enhanced IR may be a feasible approach to decrease the incidence of infectious and metabolic diseases in the dairy industry.

Characterization of a Staphylococcus aureus small colony variant (SCV) associated with persistent bovine mastitis.

Staphylococcus aureus is a common cause of bovine mastitis and foodborne and other diseases in humans. This study tested the hypothesis that small colony variants (SCVs) of S. aureus are implicated in chronic bovine mastitis. Six S. aureus isolates from foremilk samples from 11 chronically infected cows were investigated. Five isolates had typical morphology and were hemolytic and coagulase positive; one was a heterogeneous population of typical and SCV phenotype (tiny nonhemolytic colonies). In the presence of gentamicin, three of the previously typical S. aureus developed SCVs that were confirmed as S. aureus by biochemical and genetic analyses; these SCVs reverted to the typical form on antibiotic-free medium. The SCV isolate (Heba3231) from the heterogeneous population had a slow growth rate and prolonged lag phase and did not revert during 10 h of incubation. Transcriptional analysis showed that SCV Heba3231 had reduced expression of agr, hla, and coa and increased expression of indicators of fermentation pathways compared to the parent strain. Invasion of and persistence in a primary culture of bovine aortic endothelial cells (BAEC) showed that SCV Heba3231 had minimal deleterious effects, whereas the parent strain or the Newbould 305 strain caused severe damage. Recovery of the parent strain from BAEC yielded a mixture of the parent and SCV phenotypes. This study reports for the first time the isolation of S. aureus SCV from persistent bovine mastitis and suggests that SCV may be an important contributor to the prolonged survival of S. aureus in some cases of mastitis.