Phenotypic and genetic parameters of acquired immune responses to improve dairy cattle health
Bovine infectious diseases cause economic loses and food-safety concerns. Both antibody (AMIR)- and cell (CMIR)-mediated immune responses (IR) are quantitative trait candidates for broad-based disease resistance. The objectives of this thesis were to evaluate phenotypic and genetic parameters of both AMIR and CMIR in a research herd (n = 232 lactating Holstein cows) herd and a large commercial herd (n = 871 periparturient Holstein nulliparous heifers and cows) using Quil A, Freund's complete aduvant (FCA) or ' Escherichia coli' J5 vaccine as adjuvants. Antibodies to ovalbumin (OVA) and hen-egg white lyzozyme (HEWL) that included total IgG, IgM, IgG1 and IgG2 isotypes as well as 'C. albicans'-induced interferon-[gamma] (IFN-[gamma]) were measured by enzyme-linked immunosorbent assay (ELISA). Delayed-type hypersensitivity (DTH) to 'Candida albicans' was evaluated at 0, 6, 24 and 48 h post-intradermal injections. Genetic parameters and breeding values (EBV) were estimated using animal mixed models, and both phenotypic and EBV correlations of AMIR and CMIR with production, health, fertility and conformation traits were calculated. Cows were classified as high (HR), average (AR) and low (LR) responders based on phenotypic IR and EBV. Differential gene expression of HR and LR cows was evaluated using microarray analysis. Results indicated significant AMIR to OVA and HEWL. 'C. albicans ' induced significant DTH response, similar to that of mycobacteria with characteristic mononuclear cell infiltration and interferon-[gamma] production. Both HEWL and 'C. albicans' induced significant IgG1 and IgG2 antibody responses but the ratio IgG1/IgG2 antibody to candin was significantly smaller than that of antibody to HEWL. Heritabilities of AMIR and CMIR ranged from 0.12-0.42 and 0.15-0.54, respectively. Genetic correlations within AMIR and CMIR were close to one. Estimated BV for AMIR was significantly correlated with milk yield (-0.18 to -0.23), protein % (0.27 to 0.3), fat % (0.18), number of services of heifers (0.18), first service to conception of heifers (0.18), calving ease (-0.23), non-return rate heifer (0.21) and cow (0.15) and four conformation traits. Estimated BV for CMIR was significantly correlated with protein % (-0.15), daughter fertility (-0.22), non-return rate heifer and cow (-0.22), herd life (0.16) and six conformation traits. Microarray analysis showed HR and LR differential gene expression that included transcription factors, cytokines, MHC and T-cell receptor-related genes as compared to average responders.