Submitted to: American Dairy Science Association Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 7/23/2002
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Development and modulation of immune competency in calves during the first months of life is not well described. The purpose of this study was to characterize age-related changes in the functional capacities of PMN and MNL populations from young calves. Milk replacer-fed calves were nonvaccinated (NVAC, n=12) or vaccinated subQ (VAC, n=12) with BCG at 1 and 7 wk of age. Functions of PMN and MNL populations from blood samples collected at 0 (vaccinated), 2, 5, 6 (boosted), 7, 8 and 11 wk of the study period were evaluated in vitro. Yearling heifers (n=4) were vaccinated and sampled concurrently with the calves. DNA synthesis by nonstimulated calf MNL exceeded (P less than .05) synthesis by nonstimulated adult MNL from wk 2-11. Pokeweed mitogen-induced DNA synthesis by calf MNL was lower (P less than .05) than adult MNL at wk 0 only. Responses of VAC MNL to eliciting antigens (PPD and M. bovis whole cell sonicate) were evident at more than 2 wk after primary vaccination and frequently were not different from adult MNL demonstrating competency of adaptive-arm of the neonatal calf¿s immune system. Quantification of CD4, gamma/delta TCR+, and CD8 T cells in 48 h cultures by flow cytometry (wk 6 only) indicated that vaccination, age (calf vs. adult), and type of stimulation affected (P less than .05) cell proliferation. Changes in cervical skin-fold thickness after intradermal administration of PPD (wk 11) were pronounced and comparable to VAC and adults. Nonvaccinated calves did not respond to PPD. PMN function (iodination and cytochrome C reduction) was affected by age (P less than .05), but not vaccination. These results indicate that the calf vaccinated at 1 wk of age is capable of developing a vigorous response to antigenic challenge in vitro and in vivo. Hyporesponsiveness of the neonate¿s PMN and MNL populations to non-antigenic stimulation may be linked to its developmental immaturity.