EXPERIMENTAL INOCULATIONS WITH OSTERTAGIA-OSTERTAGI OR EXPOSURE TO ARTIFICIAL ILLUMINATION ALTER PERIPHERAL CORTISOL IN DAIRY CALVES (BOS-TAURUS)

A series of experiments were conducted on dairy calves (Bos taurus) to assess, by way of circulating cortisol, the impact of a parasitic inf ection as a systemic stressor.The first study was designed to assess t he effects of chronic stress on dairy calves resulting from a large bo lus inoculation of the nematode parasite, Ostertagia ostertagi. Periph eral cortisol concentrations and adrenal cortical competency to adreno corticotropic hormone (ACTH) challenge were utilized as indicators of chronic stress for 5 weeks. Calves were cleared of nematodes by anthel minthic treatment after the third week of infection. Calves were chall enged with ACTH on weeks 0 and 2, and blood samples were obtained at a 12 x 10-min bleeding schedule. Cortisol concentrations were significa ntly higher (P < 0.05) in the infected calves than in the uninfected c alves. The maximal response level to the ACTH challenge was also highe r while the calves were infected. Two additional experiments were cond ucted to investigate the effects of experimental procedures that becam e evident during Experiment 1. Firstly;, calves that had previously be en fitted with jugular cannulae were sampled from 3 hr predawn until 5 hr after dawn under red- or white-light incandescent illumination. Ca lves under red lights had lower initial cortisol concentrations but in creased to the concentrations in calves under white lights, indicating a compounding effect of lighting with the procedures of blood-sample acquisition. Secondly, 12 calves were inoculated with 10,000, 100,000, or 200,000 third-stage, infective larvae of 0, ostertagi. Blood sampl es were obtained similarly to the regimen in Experiment I. Cortisol co ncentrations were elevated only in the 200,000-dose group during week 3, correlating with the period immediately after emergence of the youn g adult parasites from the gastric glands. Continuous emergence of the se parasites might induce chronic hyperadrenocorticism and the concomi tant negative consequences on metabolic and immunological processes. P ublished by Elsevier Science Inc.