# Retained Placenta as a Potential Source of Mastitis Pathogens in Dairy Cows
## 4 Discussion
A significant prevalence of yeast contamination from the mammary glands of dairy cows has been reported in some countries such as Mexico (25.8%; 282/1095; [54]) and Algeria (10.2%; 114/1121; [55]). In a recent and large study (Japan) [56], from 18,915 bulk tank milk samples in 1,088 bovine farms, 184 isolates of yeast species were detected. _Pichia kudriavzevii_ (\(n\) = 97 isolates), _Kluyveromyces marzianus_ (\(n\) = 28), _C. akabanensis_ (\(n\) = 21), _C. parapsilosis_ (\(n\) = 13) and _P. catcophilla_ (\(n\) = 12) were isolated, highlighting their relative importance (1% of the samples) in mastitis prevalence. However, contamination of bulk milk by environmental saprophytes yeasts can also occur. Therefore, more attention is required to establish the impact of yeasts on reproductive health in dairy cows. In our study, similar intrauterine prevalence was observed for _T. pyogenes_/_P. indicicus_ (80.0%; 95% CI: 54.8\(-\)93.0%) and _Strep. uberis_ (78.6%; 95% CI: 52.4\(-\)92.4%). It has been previously observed by [PERSON] et al. [10] that the _T. pyogenes_ prevalence correlates (\(p\) < 0.001) with that of _Peptoniplilus_ spp. on day 3 postpartum in uterine fluid, with _T. pyogenes_ prevalence reaching its maximum (52.5%; 64/122) on day 15 [10]. A similar pattern was also found by [PERSON] et al. [2]. Regarding the differences in _T. pyogenes_ prevalence between both studies, it is necessary to investigate if the presence of RP increases the risk of _T. pyogenes_ contamination during the first days postpartum, and if the physical presence of the placenta membrane enhances that risk. Mastitis caused by this bacterium has been related to summer mastitisitis [28; 57]. This may be explained by the increased number of vectors (_Hydrotaea irritants_) able to transmit _T. pyogenes_[58]. _Strep. uberis_ is considered a major mastitis pathogen with high genetic variability in the environment and animal udders [59]. It is also a bacterium that frequently colonizes the uterus postpartum, and a dynamic interaction between _Strep. uberis_ and _T. pyogenes_ has been described [2]. _Strep. uberis_ is also a commensal microorganism of the bovine gut [60]. Thus, transmission to the udder via the digestive tract and feces is considered one of the most relevant routes of udder contamination [61], and the same is probably true for uterine contamination. Interestingly, 54.5% of the cows positive for _Strep. uberis_ presented fever, whereas this clinical sign was not observed in any other cow. We did not find any study on this issue. _Strep. uberis_ mastitisitis is often sudden in terms of its onset, and produces a hard, swollen quarter, with large white clots in milk, and sometimes with a high, or very high, body temperature [62]. In fact, this infection in dairy cows causes major signs of clinical mastitis, in some cases associated with systemic reactions [63]. _Strep. uberis_ is recognized as an inducer of fewer due to its involvement of systemic cytokines [64; 65]. Apparently, according to our study, similar pathogenesis may occur when the infection is intrauterine. _Strep. dysgalactica_ is other relevant contagious mastitis pathogen with previous scarce detection in the uterus, during the early postpartum period [66; 67]. In contrast, we detected it in a high proportion of cases (57.1%; 8/14) in our study. There is evidence that _Strep. dysgalactica_ can persist for more than one year on the environment in dairy farms [63]. Hence, the importance of _Strep. dysgalactica_ in the Puereral uterus should be evaluated. Finally, as expected, except for _E. coli_, a fair (_Strep. uberis_; k = 0.34; \(p\) < 0.05) or non-significant agreement (_Enterococcus_ spp., _Strep. dysgalactica_; \(p\) > 0.05) was observed between RT-PCR and bacterial culture methodologies, confirming the latter as useful especially for challenging bacterial cultures (e.g., _Mycoplasma_). In fact, the better performance of a multiplex PCR assay than that of bacterial cultures considering mastitis pathogens has previously been reported [68; 69].