The dry period poses an extraordinarily high risk of new infections for the bovine mammary gland. Environmental pathogens are of particular importance during this time. Normally, an infection during the dry period does not cause clinical symptoms, but is often responsible for clinical mastitis in the first weeks of lactation. Reducing new infections in dry cows can significantly decrease mastitis incidence in early lactation. During the course of the dry period, the new infection rate does not remain constant, but peaks immediately after drying off and shortly before calving. The chance of a new infection is influenced multifactorially by the animal, pathogen and environment. In this context, the closure of the teat canal using a keratin plug is very important. There are different approaches to antibiotic dry cow treatment. Either all udder quarters of all dry cows are treated (blanket dry-cow treatment) or just the udder of animals with a proven infection or an increased somatic cell count (selective dry-cow treatment). In the latter case, all udder quarters of an animal may be treated or just the one in which the infection or the increased somatic cell count was found. Instead of, or as a supplement to antibiotic treatment, teat sealers can be used. They support or take over the function of the keratin plug by closing the teat canal. In addition, there are some alternative methods to prevent new infections. Nevertheless, reducing the risk of infection is of primary importance. For this purpose, there are numerous options for improving hygiene in the environment of dry cows.