Uloga oksidacijskog stresa i upalnog odgovora u patogenezi mastitisa u mliječnih krava

Mastitis is one of the most frequent diseases of dairy cows throughout the world, therefore it causes the greatest economic losses in dairy cattle industry. These losses are reflected through: reduced milk production, increased costs of medication and the other animal health services, reduced fertility, early culling of animals and the value of discarded milk. Mastitis is also important from the aspects of public health, milk processing and animal welfare. In the pathogenesis of mastitis the key role plays the innate immune response which is the first line of defence against the pathogen invasion of the udder. The innate immune response generates an inflammatory reaction which is the elementary response of an organism to the tissue trauma induced by any physical, chemical or biological causative agent, but primarily it is the protective mechanism of a vital significance which includes increased phagocytic activity, secretion of antimicrobial substances, fibrosis as well as the alterations in tissue structure of affected organ or body cavity. The release of a number of inflammatory mediators as well as reactive oxygen species (ROS) is an important part of inflammatory response. In dairy cows, the metabolic challenge that occurred during the transition from dry period to early lactation may additionally increase the release of ROS which may contribute to development of oxidative stress and inflammatory response. Oxidative stress is defined as a shift in the balance from cellular oxidation-reduction reactions towards oxidation, i.e. to the state of excessive release of oxidants when their removal by antioxidants is impaired and even insufficient. During peripartum period antioxidantive status of dairy cows is seriously impaired and consequently both the oxidative stress and inflammatory response may present the predisposing factors to their higher susceptibility to intramammary infections (IMI) and mastitis. This association between oxidative stress and inflammation during IMI and mastitis indicates their role in the pathogenesis of mastitis. Thus, a better understanding of such a synergism could contribute to development of new approaches to prevention and therapy of IMI and mastitis.Mastitis je jedna od najčešćih bolesti mliječnih goveda u cijelom svijetu, jer uzrokuje najveće gubitke u mliječnom gospodarstvu. Ima značajan utjecaj sa stanovišta javnog zdravstva, prerade mlijeka i dobrobiti životinja. Ekonomski gubitci se očituju kroz: smanjenu proizvodnju mlijeka, velike troškove liječenja, prijevremeno izlučivanje životinja, vrijednost odbačenog mlijeka te smanjenu plodnost. U patogenezi mastitisa ključnu ulogu ima urođeni imunosni odgovor koji je prva linija obrane nakon što patogen prodre u mliječnu žlijezdu. Upala je standardna reakcija organizma na ozljedu bilo kakvog fizičkog, kemijskog ili biološkog uzroka, no prije svega to je vitalni zaštitni mehanizam, koji uključuje proizvodnju reaktivnih kisikovih spojeva (ROS), fagocitne mehanizme, izlučivanje protumikrobnih tvari, stvaranje ožiljkastog tkiva i neovaskularizaciju te promjene tkivne strukture zahvaćenog organa ili tjelesnog prostora. Metaboličko opterećenje nastalo prilikom prelaska iz perioda zasušenja u period rane laktacije je dodatno potencijalni izvor oksidansa i ROS-a u mliječnih krava i pogodovni čimbenik za nastanak oksidacijskog stresa i upalnog odgovora. Oksidacijski stres definiran je kao pomak ravnoteže u staničnim oksido-redukcijskim reakcijama prema oksidaciji, odnosno to je stanje prekomjernog stvaranja slobodnih radikala kisika i ROS pri čemu se nadilazi mogućnost njihova uklanjanja. Antioksidacijski status krava u peripartalnom periodu je stoga oslabljen i posljedično oksidacijski stres i upalni odgovor mogu predisponirati osjetljivosti krave za intramamarne infekcije (IMI) i mastitis. Povezanost između upalnog odgovora i oksidacijskog stresa tijekom IMI i mastitisa ukazuje na njihovu važnu ulogu u patogenezi bolesti mliječne žlijezde te stoga bolje razumijevanje takvog sinergizma može doprinijeti razvoju novih pristupa u prevenciji i liječenju IMI i mastitisa