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.

Yeasts are always present in any type of cheese, as well as in the factories where it is produced. However, the role of the yeast community in the cheese making process, as well as the routes of contamination used by yeast species to contaminate milk from the dairy farm environment, are not well known. The objectives of this study were to broaden the knowledge of the dominant yeast community in Manchega sheep’s milk and to assess the contamination routes of the yeast species depending on the farm practices. Milk, teat surface (collected from ten ewes per farm), feed, and air (collected in milking parlours and livestock housing) samples were collected from 12 typical farms in Castilla-La Mancha, Spain with differences in farming practices, and the yeast species were identified using DNA sequencing methods. To evaluate whether certain farming practices have an effect on the distribution of species of yeast in the milk samples, a mixed model was used. The results showed that most of the dominant yeast species (mainly belonging to the genus Candida) found in milk were also found in the other samples, indicating a microbial transfer from the farm environment to the milk. Furthermore, the statistical model showed that factors influencing yeast counts in milk were the presence of yeasts in the milking parlour, the use of silage, and the frequency of acid treatment for cleaning the milking machines. In conclusion, milk contamination from the yeast species present in the dairy farm environment is related to certain farming practices such as the use of silage and the daily use of acid in the cleaning of the milking machines, which favours the presence of desirable microbiota in milk.

Milk is a typical and satisfactory medium for the growth of lactic acid bacteria (LAB). These microorganisms are of vital importance in the quality of the milk since they contribute to its preservation and give differential organoleptic properties to the final product. Furthermore, LABs can act as biocontrol agents in the dairy industry by inhibiting the growth of undesirable bacteria present in milk and by improving the quality of dairy products such as cheese. In this context, knowing the transfer routes used by LABs from the livestock environment to the milk is of great importance within the dairy industry. Therefore, the objectives of the present study were to expand the knowledge of the LAB population present in the milk of Manchego ewe by means of DNA sequencing techniques and to evaluate the possible transfers of LAB species based on the management of each dairy farm. Samples of bulk tank milk, air (from the milking parlour and from the livestock housing), animal feed and teat surface (taken from 10 sheep per farm) were collected in 12 traditional livestock farms in Castilla-La Mancha (Spain), where each farm presented differences regarding their farming practices. A mixed-effects model was used to evaluate the effects of livestock practices on the distribution of LAB species. Results showed that the vast majority of species identified in the milk had an isolate that was also found in other matrices, which could indicate a microbial transference via the livestock environment to the milk. In addition, the mixed model showed that the factors that positively influence the LAB count were the low-line milking system and the daily use of acid detergent in cleaning the milking machine.