Dry Periods-Resting cows. The dry period. The dry period is an important resting period for the dairy cow, where fresh udder tissue is formed in readiness for the lactation, and it provides an important opportunity to rid the udder of many potential pathogens that can cause mastitis.ry Periods-Resting cows. The dry period. The dry period is an important resting period for the dairy cow, where fresh udder tissue is formed in readiness for the lactation, and it provides an important opportunity to rid the udder of many potential pathogens that can cause mastitis.