|dc.description.abstract||The studies described herein were designed to characterize measures of immune responsiveness in weaned Brahman calves, breeding bulls and cows. Experiment 1 included 55 weaned bull and 57 weaned heifer Brahman calves. Experiment 2 included 84 sexually mature, non-pregnant Brahman cows, 33 cows in early stages of pregnancy (d1-97), 60 cows in mid-pregnancy (d98-194), 71 cows in late pregnancy (d195-292), and 25 fertile bulls. Antibody mediated immune response (AMIR) was determined by a vaccine specific IgG, enzyme linked immunosorbent assay (ELISA) in response to cattle receiving Salmonella Newport Extract vaccine. Cell mediated immune response (CMIR) was determined by a subcutaneous (neck) sensitization dose of 25x103 protein nitrogen units (PNU) Candida albicans with 750 µg Quil-A adjuvant on day 0. On day 14 caudal skin fold thickness (SFT) was measured using Harpenden calipers prior to intradermal injection of 5x103 PNU CA into the skin fold and on day 15 the injection site SFT was measured again. Response was determined by the difference in SFT from day 15 (postinjection) and day 14 (pre-injection).
In Experiment 1 with immature cattle, the CMIR was greater (P < 0.05) in bulls than heifers; however, AMIR did not differ between bulls and heifers. In weaned Brahman calves AMIR was not influenced by sex; however, there was sexual dimorphism associated with CMIR, in that bull calves had a greater response than heifers (P < 0.05).
In mature Brahman cattle, the mean CMIR was lowest in non-pregnant cows relative to pregnant cows (early, middle, and late) and bulls. Stage of pregnancy did not affect CMIR nor did fertile bulls and pregnant cows differ in CMIR. Regarding AMIR, fertile bulls and non-pregnant cows did not differ. Although AMIR did not differ between non-pregnant and early pregnant cows, stage of pregnancy was a factor as AMIR was least in the middle and late pregnant cows. Physiological status, stage of pregnancy, and sex should be considered when evaluating either cellular or antibody mediated immune response in mature Brahman cattle. Selection of high immune responding animals could lead to improved health, productivity, and a decreased reliance on antimicrobials.||en