# Retained Placenta as a Potential Source of Mastitis Pathogens in Dairy Cows
## 4 Discussion  
In this study, 60% (9/15) of the mastitis pathogens that could be identified via RT-PCR MastiType Multi Kit were detected in the uterine fluid of cows with RP. Of these pathogens, 40% (6/15) were isolated in more than half of the cows. The microorganisms were mainly (66.7%; 6/9) environmental mastitis pathogens (_E. coli_, _Staphylococcus_ spp., _Strep. uberis_, _Enterococcus_ spp., _T. pyogenes/P. indolicus_, yeasts). As previously mentioned, when the cervix opens at calving, environmental bacteria and yeast (e.g., vaginal and fecal) contaminate the uterus, usually up to two weeks after calving [27]. _Strep. dysgalacticue_, _Strep. agalacti_ and _Mycoplasma_ spp. are considered contagious mastitis pathogens [28; 29], i.e., their main route of transmission occurs from udder (mammary gland) to udder through milking procedures carried out with contaminated milking equipment. However, environmental spread also occurs, and these pathogens can be classified as both environmental and contagious pathogens (see the review by [PERSON] et al. [29]). _Mycoplasma_ spp., e.g., _M. boyegnetlium_ and _M. californicum_ (9.3%; 3/32), have also been detected previously in vaginal [30] and milk samples [31] from dairy cows. In cattle, uterine microbiota is established within 20 min after calving [17]. At that time, the decomposing placental membrane and lochia provide an optimal intrauterine environment for microorganisms' colonization and growth [32; 33]. In turn, the discharge of uterine secretions contributes to the spread of (normal and pathogenic) bacteria. It was observed by [PERSON] et al. [34] that the total bacteria load in the vagina was similar at the day of calving in cows with or without RP. Nonetheless, a tendency (\(p\) = 0.06) on day 3 postpartum and on day 7 postpartum of a significantly larger (\(p\) < 0.001) total bacteria load (bacterial/archae1 16S rDNA gene), in cows with RP rather than in healthy cows, was observed in their study [34]. These differences highlight the relevance of environmental bacteria spreading to RP animals. In our study, _E. coli_ and _Staphylococcus_ spp. were the bacteria most frequently detected in the uterine fluid. Likewise, _E. coli_ has been reported by [PERSON] et al. [4] as the most prevalent bacteria in the uterus, in early postpartum in cows with or without RP. Moreover, it was observed by [PERSON] et al. [35] that cows with RP were 45 times more likely to present _E. coli_ during the first three days postpartum than cows without it (odds ratio = 44.8; \(p\) < 0.01). _E. coli_ is also the most frequently found Gram-negative pathogen causing acute clinical mastitis during early lactation in high-producing dairy cows. It invades the udder through the teats, proliferates, and induces a local and systemic acute phase response that may cause irreversible tissue damage in the mammary gland, and severe clinical symptoms, sometimes even leading to the animal's death [1; 36]. _E. coli_, as with other microorganisms, is a ubiquitous and opportunistic pathogen that depends on intrinsic virulent factors [37], bacterial load [38], and immune, metabolic and oxidative status to cause disease [6; 34]. During the transition period and mainly around parturition, the increased energy demand favors the incidence of metabolic diseases, compromising immunity and resistance to infections by pathogenic and opportunistic agents. The condition of RP increases the occurrence of postpartum infectious diseases via uterine colonization and the development of _E. coli_ and other microorganisms [9; 39]. In the same way, the negative energy balance during this period impairs the immune response in