Oral and Poster Abstracts

vaccinated (Group II) with Pastobov (the vaccine manufactured by
Merial consist of M. haemolytica A1 leukotoxoid). The alternations
were investigated in peripheral blood leukocyte subpopulations
using flow cytometry (FCM) in the calves experimentally challenged
by intravenous administration of 25 µg of M. haemolytica A1
leukotoxin per animal. The experimental calves (Group I) 21 days
before the challenge were vaccinated with intramuscular injection of
Pastobov (2 mls i.m.). The calves were next compared with the
control animals (Group II - non-vaccinated). The comparing studies
were performed just before (0) and 1, 2, 3, 4, 5, 6 and 24 hrs after the
challenge. The following parameters were assayed: white blood cell
count (WBC), percentage of polymorphonuclear leukocytes
(PMNL), mid-size leukocytes (MID), i.e. total value of monocytes,
eosinophils and basophils, total percentage of lymphocytes (LYM)
and their subsets: CD2 + (T lymphocytes), CD4 + (T helper
lymphocytes), CD8 + (T suppressor/cytotoxic lymphocytes) and
WC4 + (B lymphocytes). A part from that the clinical signs were
recorded during the study such as rectal temperature, heart and
respiratory rate and general behaviour of the affected animals. The
obtained results of the study showed, that in peripheral blood WBC
and the percentages of MID, PMNL, LYM and their some
subpopulations (CD2 + , CD4 + , CD8 + cells) markedly decreased
(leukopenia) in both groups of the affected animals especially during
the first of third hours of the experiment. However, these changes
were more significant (P