The extent of postpartum negative energy balance in dairy cows is positively associated with body condition score (BCS) at calving. Results of epidemiological studies have indicated that calving BCS is positively correlated with several indicators of immune dysfunction during the post-partum period. Metabolites of negative energy balance (NEB) have been associated with impaired lymphocyte and neutrophil function in vitro. Therefore, cows that calve in greater condition might exhibit a greater degree of periparturient immune dysfunction than thinner cows. The objective of this thesis was to investigate the effect of BCS at calving on adaptive immune function, using in vivo measures. Two experiments were conducted using dairy cows in the DairyNZ Lye farm herd. The first experiment determined the level of background exposure to Candida albicans. Delayed-type hypersensitivity (DTH) to C. albicans is used as an indicator of cell-mediated immune response (CMIR) in cattle. Prior immunisation against C. albicans ensures measurable DTH responses from most cows. However, if natural exposure to C. albicans is high or variable, background DTH must be measured before immunisation, or an alternate antigen used. To determine background DTH responses in pasture-based cows, responses of ten unimmunised and ten immunised cows were compared. A greater proportion of immunised versus unimmunised cows mounted a positive DTH response (90% vs. 70%), and responses were larger (P < 0.01) and more variable (P < 0.05) in immunised cows. Results indicate that pasture-based cows in New Zealand have consistently low background exposure to C. albicans. Therefore, C. albicans is an appropriate antigen for inducing DTH responses as an in vivo measure of CMIR in pasture-based cows. The second experiment tested the hypothesis that BCS at calving affects immune function. The energy balance of sixty healthy cows with similar mid-lactation BCS was manipulated in late-lactation to achieve three homogenous BCS groups of twenty cows at calving, with calving BCS of 3.4, 4.6 and 5.4 (NZ BCS scale of 1 to 10). Antibody-mediated immune responses (AMIR) and cell-mediated immune responses (CMIR) measured postpartum were compared with responses measured in mid-lactation before BCS manipulation began. Calving BCS had no effect on the magnitude of AMIR (P = 0.93) or CMIR (P = 0.99), and did not affect the ratio of antigen-specific IgG1 and IgG2 produced during AMIR (P = 0.48). These results indicate that, within the range of BCS at calving investigated, and the associated degree of postpartum NEB did not influence ability to mount adaptive immune responses in vivo. Cows calving within the BCS range examined (between 3.4 and 5.4) did not differ in AMIR or CMIR; therefore, the results support the current recommendations regarding optimal calving BCS for mature cows, and support the minimum BCS allowed by the welfare code.