This review attempts to reflect the importance of different factors that affect the environmental quality of dairy farms and must, therefore, be taken into account when considering the importance of environmental microbiology as a tool in the improvement of the quality of milk and dairy products. The effect of a factor such as temperature is vital for the dairy farm environment, especially when the temperatures are extreme, because a proper choice of temperature range improves the quality of the air and, thus, animal welfare. Similarly, the appropriate level of relative humidity in the environment should be taken into consideration to avoid the proliferation of microorganisms on the farm. Air quality, well-designed livestock housing, proper hygienic practices on the farm, stocking density, and the materials used in the livestock houses are all important factors in the concentration of microorganisms in the environment, promoting better welfare for the animals. In addition, a ventilation system is required to prevent the pollution of the farm environment. It is demonstrated that proper ventilation reduces the microbial load of the environment of dairy farms, enhancing the quality of the air and, therefore, the wellbeing of the animals. All this information is very useful to establish certain standards on dairy farms to improve the quality of the environment and, thereby, achieve better quality milk and dairy products.

Mastitis is a highly prevalent condition that has a great impact on milk production and animal welfare, and often requires substantial management efforts. For this reason, it is generally considered an important threat to the dairy industry. Many microbial, host, and environmental factors can protect against, predispose to, or influence the development of mastitis. The objective of this work was to characterize the milk microbiota of Manchega ewes, and to compare samples from animals with and without a history of mastitis. We analyzed milk samples from 36 ewes belonging to 2 different farms (18 ewes from each farm) using culture-dependent and culture-independent techniques. We also analyzed several immune compounds to investigate associations of mastitis with 3 main variables: farm; history of mastitis or no mastitis; and parity number. Both culture-dependent and culture-independent techniques showed that ewe milk harbored a site-specific complex microbiota and microbiome. Staphylococcus epidermidis was the main species driving the difference between farm A (where it was the dominant species) and B (where it was not). In contrast, samples from farm B were characterized by the presence of a wide spectrum of other coagulase-negative staphylococci. Some of these species have already been associated with subclinical intramammary infections in ruminants. Of the 10 immune compounds assayed in this study, 3 were related to a history of mastitis [IL-8, IFN-γ, and IFN-gamma-induced protein 10 (IP-10)]. Increases in IL-8 concentrations in milk seemed to be a feature of subclinical mastitis in sheep, and in this study, this immune factor was detected only in samples from ewes with some episodes of mastitis and from the group with the highest somatic cell count. We also observed a positive correlation between the samples with the highest somatic cell count and IFN-γ and IP-10 levels. Our results suggest that these 3 compounds could be used as biomarkers for the negative selection of mastitis-prone animals, particularly when somatic cell count is very high.