INTRODUCTION
Bovine mastitis is a common disease on dairy farms and leads to enormous economic losses worldwide (Angelopoulou et al., 2018; Sathiyabarathi et al., 2016). Escherichia coli is one of the most common mastitis-causing pathogens and often leads to acute mastitis with a severe inflammatory response that damages the blood-milk barrier. The abuse of antimicrobials in food animals has attracted public attention as concerns relating to antimicrobial residues and anti-microbial resistance in bacteria have increased because of the increased use of antimicrobials (Muziasari et al., 2016; Lhermie et al., 2016). Therefore, there is an urgent need to find new potential non-antimicrobials for mastitis prevention.
Lactobacillus is a probiotic that plays an important role in the immunity and health of animals. Their probiotic properties play an important role in regulating gut microbiota (Igor et al., 2019), relieving intestinal diseases (Sanders et al., 2019), and enhancing body immunity (Garcia-Castillo et al., 2019) in addition to other functions (Li et al., 2017; da Costa et al., 2019). Lactobacillus is known to protect hosts during intramammary infection in both humans and cows by oral or intramammary administration (Fernández et al., 2016; Arroyo et al., 2010; Jiménez et al., 2008), but the underlying mechanism of this protective effect remains unclear. Intramammary injection of drugs is the most common and effective way for treating bovine mastitis in practice, as intramammary injection of some Lactobacillus strains can effectively alleviate clinical symptoms of bovine mastitis (Ignacio et al., 2015; Pellegrino et al., 2017; Kitching et al., 2019). Oral administration of Lactobacillus casei Zhang (LCZ ) isolated from naturally fermented mare’s milk is effective for alleviating the clinical symptoms of mastitis in mice (Ma et al., 2018). However, whether intramammary injection of LCZ has a prophylactic effect on mastitis, as well as its underlying mechanism, remains unclear. Here, we studied the prophylactic effect of LCZ by intramammary injection onE. coli -induced mastitis.