Role of bacterial endotoxins in the etiopathogenesis of periparturient diseases of transition dairy cows.

Discipline: disease; Key words: bacterial endotoxins, dairy cows, periparturient diseases

The dairy industry continues to experience severe economic losses due to the increased disease incidence high-producing cows experience during the transition period. Typically, these diseases manifest as milk fever, ketosis, fatty liver, ruminal acidosis and even reproductive disorders such as metritis. It has long been the classical view that the major contributing factor to the development of these diseases is the considerable increase in nutritional demands for milk production. This classical view, however, fails to account for the substantial correlation between both metabolic and infectious diseases and the detrimental effects that can occur with the provision of high-energy diets to support these nutritional demands. The status of current knowledge and thought has recently been reviewed by Drs E. Eckel and B. Ametaj, the review being published in the Journal of Dairy Science, Volume 99 of 2016, page 5967 to 5990. The title of the review is: Role of bacterial endotoxins in the etiopathogenesis of periparturient diseases of transition dairy cows.

Evidence is increasing to show that high-energy diets is overburdening the metabolic system of the cow resulting in peroxidation of endproduct molecules, stress and immuno-modulatory responses which may be exploited by bacterial endotoxins. Bacterial endotoxins are components of the outer cell wall of gram-negative and gram-positive bacteria that are highly immune-stimulatory and can trigger inflammatory immune responses. The ability of endotoxins to translocate from the mucosal tissues, including the gastrointestinal tract, udder and uterus, into the bloodstream has been observed. Once they have entered the circulation, endotoxins potentially contribute to disease either directly, through eliciting an inflammatory response, or indirectly through other factors such as the overreaction of the natural protective mechanisms of the host. The authors, however, warn that whereas the evidence implicating a role of endotoxins in the pathogenesis of transition diseases continues to grow, current knowledge of the host response to endotoxin exposure and pathogenic mechanisms remain largely unknown. What is nevertheless promising is that better understanding of the connection between endotoxaemia and dairy cattle disease holds significant potential for the future development of preventative measures that could benefit productivity as well as welfare of the cow.