Renata Urban-Chmiel
The influence of transport stress on susceptibility of cattle and sheep on Mannheimia haemolytica leukotoxin
A bovine respiratory distress syndrome, also termed enzootic bronchopneumonia, mannheniosis and shipping fever, constitutes one of the key health problems occurring in the feedlot cattle herds as well as in other ruminants, like sheep and goats. Increased incidence and mortality, decreased body weight gains, lesser feed utilization and high financial costs of prophylaxis and therapy lead to enormous economic losses in this sector of animal production. Among the numerous views expressed, an opinion prevails that besides some species predispositions and infectious agents (viruses and bacteria) a stress, especially connected with transportation, proves to be one of major factors which is likely to develop an animal disease and death. Immediately after transport, an increased percentage of animals with of M. haemolytica strains isolated from the respiratory tracts that confirms attenuation of protective mechanisms against infectious agent. Whereas, the changes observed throughout the stress response course affect the colonization and adhesion of M. haemolytica strains in the cattle and sheep respiratory tracts under transport conditions.
Owing to complex etiology including many infectious agents and environmental stressors as well as differentiated age of the animals prone to disease incidence, undertaking the appropriate preventive measures that would limit a morbidity rate poses a significant challenge. The commercial vaccines containing a number of antigenic components obtained from the pathogens contributing to the respiratory distress syndrome development do not protect from a disease, while the immune response obtained is short-term.
The presented reports the assessment of a stress reaction effect on the immune cells activity in animal protection against the results of M. haemolytica induced infection. Another research element was to evaluate the impact of cortisol, elevated temperature and LPS under in vitro conditions on the basic metabolic processes and immune of leukocytes.
Immediately prior to and after the cattle and sheep transportation and unloading, the animals were analyzed in terms of the natural behaviour, evaluation of temperature, pulse and respiratory rate based on the clinical examinations and animal observations. The following stage consisted in the assessment of the cattle and sheep transportation influence on the hormonal balance (concentration of cortisol and 11.17DOA), organism immune parameters as well as the antioxidative/oxidative status. Regarding leukocytes, there was also determined their susceptibility degree to cytotoxic activity of Lkt M. haemolytica serotype 1 and Ltx Actinobacillus actinomycetemcomitans.
The present studies demonstrated a strong correlation between the cattle and sheep transportation and the homeostasis disorders expressed by, among others, elevated temperature, increased concentration of steroid hormones, mainly cortisol and its metabolite 11.17DOA, disturbance of the antioxidative/oxidative status balance with oxidation process predominance, immune indices change and finally, increased susceptibility of immune cells to the cytotoxic activity of Lkt M. haemolytica. The results of this research study explicitly indicate a significant influence of the cattle and sheep transportation on increase of leukocytes sensitivity to the cytotoxic effect of Lkt M. haemolytica. The expression growth of b 2 -integrine receptors in the leukocyte membrane and a significant correlation (r>0,05) between a percentage of the leukocytes susceptible to Lkt suggest a substantial contribution of these agents to the increased susceptibility of cattle and sheep on diseases with the respiratory syndrome signs. The obtained results confirm the assumption dealing with specific affinity between Lkt M. haemolytica and the bovine leukocytes and those isolated from sheep.
Despite the observed growth of b 2 -integrine receptors facilitating the enhanced adhesion of leukotoxins of Gram-negative bacteria to leukocytes, there was not observed elevated sensitivity of the cells isolated from the animals after transportation to the cytotoxic effect of Ltx of A. actinomycetemcomitans cells.
Summing up,it should be emphasized that transport of cattle and sheep, irrespective of its duration time, makes up a very strong agent inducing a stress response generation. As a consequence, it was shown to exert a profound impact on the basic physiological processes disturbance manifested by temperature increase, change in the antioxidative/oxidative status, immune indices alteration as well as greater susceptibility of leukocytes to the cytotoxic effect of Lkt M. haemolytica. Enhanced sensitivity of leukocytes to Lkt clearly indicates a substantial contribution of stress transportation as a key agent that predisposes the cattle and sheep towards respiratory syndrome production with this bacteria.
Simultaneous growth of b 2 -integrine receptors expression recorded in the leukocyte membrane as well as high correlation between this process and a percentage of cells sensitive to Lkt suggest the potential employment of this indicator in the as sessment of cattle and sheep proneness to a respiratory syndrome disorder induced by M. haemolytica immediately after transport.
Enlargement of the antioxidant potential in transported cattle and sheep may have a serious impact on a rise of the leukocyte resistance towards the cytotoxic activity of Lkt that also affects efficiency of cellular resistance mechanisms. From the present research results and some suggestions from the other authors, it seems supplemented to administer greater amount of antioxidants commonly with used prophylaxis to the cattle and sheep at the pre- and immediately after transport period.