# Retained Placenta as a Potential Source of Mastitis Pathogens in Dairy Cows
## 4 Discussion
\begin{table}
\begin{tabular}{l c c c} \hline \hline \multicolumn{1}{c}{**Bacteria**} & \multicolumn{1}{c}{**Agreement between Methods**} & \multicolumn{1}{c}{**Cohen’s Kappa Coefficient**} & \multicolumn{1}{c}{
\begin{tabular}{c} **Number of Isolates BC- and** \\ **RT-PCR+ (1)** \\ \end{tabular} } \\ \hline _E. coli_ (_n_ = 15) & 93.3\% & 0.64 (substantial) ** & 1 \\ \hline _Strep. uberis_ (_n_ = 14) & 64.3\% & 0.34 (fair) * & 5 \\ \hline _Enterococcus_ spp. (_n_ = 15) & 60.0\% & 0.15 (slight) & 6 \\ \hline _Strep. dysgalacticue_ (_n_ = 14) & 50.0\% & 0.11 (slight) & 7 \\ \hline \hline \end{tabular}  
* \(p\) < 0.01; *; \(p\) < 0.05. (1) Number of isolates negative on bacterial culture (BC) but positive on RT-PCR. The inverse occurrence (RT-PCR—and bacterial culture +) was not observed.  
\end{table} 
Table 2: Agreement in bacterial identification between RT-PCR and bacterial culture methods. the mammary gland of lactating dairy cows, increasing the susceptibility to mastitis [40; 41; 42] and RP [39]. Furthermore, oxidative stress has also been associated with negative energy balance [43; 44] and metabolic disruptions [45] in dairy cows. It was suggested that the link between RP and mastitis may be related to the weakening of the immune system [46], through peripheral leukocyte impairment [47]. Moreover, the chronological conjugation of these factors with bacterial load, including bacterial virulent factors [35], can have a relevant impact on the incidence of these diseases. Nonetheless, the common possible source for RP and mastitis does not rule out the possibility that RP plays a key role in aggravating mastitis through causing an increased level of contamination in the environment of the under of affected cows, regarding _E. coli_ and other bacteria. [PERSON] et al. [48] observed a tendency for cows with RP to have an increased risk of presenting clinical mastitis (risk ratio = 2.88; 95% CI = 0.96-8.64; \(p\) = 0.06) than cows without RP. The risk of developing severe mastitis was higher (RR = 5.4) in cows with RP than that in healthy cows. Also, cows with RP up to five days after calving were more likely to present clinical mastitis up to 120 days postpartum (odds ratio = 9.45; 95% IC = 8.62-10.27; \(p\) < 0.001) than cows without RP [49]. A large epidemiological study addressing environmental, bacterial and host factors is required to evaluate the relationship between RP and mastitis in more depth. The _Staphylococcus_ spp. group mainly comprises CNS with more than 50 bacterial species, with _S. chromogenes_, _S. epidermidis_, _S. haematyticus_, _S. stimulus_ and _S. xylosus_ being the most common CNS milk pathogens [50]. Large numbers of this species are also found in the environment and can partially explain the high proportion of _Staphylococcus_ spp. (93.3%) observed in our study as a result of contamination through the vagina in the early postpartum period. On the other hand, in recent years, CNS have been considered the most prevalent microorganisms identified in subclinical mastitis in dairy cows [51]. A high proportion of yeasts (92.9% of the cows) were detected in our study. However, detection does not mean that colonization occurs. We hypothesize that the birth channel is just the route of transmission from the environment (or vagina) to the udder. Yeats are common in the environment, on the skin, in feces and even in the vagina microbiota. They are also opportunist microorganisms (e.g., _Candida albicans_, _C. Krusei_, _C. tropicalis_), and uterine colonization is usually related to cows with specific conditions such as infertile cows, repeat breeders, cows with persistent endometritis, prolonged intra-uterine antibiotherapy, and immunosuppression [33; 52]. Nonetheless, a yeast prevalence between 21 and 33% from cervicovaginal fluids of Holstein cows (\(n\) = 176) was previously reported by [PERSON] et al. [53]. In that study, no statistically different prevalence was observed between cows with reproductive disorders (including those with RP) and non-pregnant or pregnant healthy cows.