During the last three decades, several published studies have investigated the relationship that clinical or subclinical mastitis post-calving has on reproductive performance. A meta-analysis that combined data from 29 separate studies conducted by The Ohio State University in 2019 set out to measure the effects of mastitis on the reproductive performance of dairy cows. Comparing cows with mastitis to cows with no mastitis, the authors discovered differences in the following reproductive measures:
- Increased days to first service
- Increased days open
- Differences in pregnancy per artificial insemination
- Greater pregnancy loss
This data clearly demonstrates that mastitis post-calving has detrimental effects on reproduction, providing even more incentive for dairy farms to reduce new intramammary infections (IMIs) during the dry cow period.
Importance of dry period
During the past 50 years, there has been a decrease in the prevalence of contagious mastitis pathogens and an increase in environmental pathogens, such as coliforms and environmental streps, which are abundant in the dry cow environment.
Depending on the level of management and the quality of preventive programs in place, new IMIs are typically acquired in four main areas, including (1) the milking process, (2) the lactating cow environment, (3) chronically infected cows and (4) the dry period. Although a dairy cow can develop a new IMI at any time during the lactational cycle, the dry period is the most susceptible time frame to develop new IMIs, making the dry period essential for prevention and control.
Wide fluctuations during dry period
The mammary gland exhibits wide fluctuations regarding its susceptibility to infection during the dry period. The greatest susceptibility for mastitis occurs during the first two weeks and the last two weeks of the dry period.
During the first two weeks of the dry period, discontinuation of teat dipping leads to increased numbers of bacteria at the teat ends. Termination of milking halts the natural flushing effect that milking has on pathogen removal from teat canals. Many quarters have a delay or fail to form an adequate keratin plug which helps seal teat ends from bacterial penetration. Collectively, these risk factors are reasons that dry cow therapy and internal teat sealants are recommended at dry-off to help reduce new IMI infection risk.
During the last two weeks of the dry period, colostrum production causes a renewal of udder engorgement. The keratin plug naturally breaks down just prior to calving. White blood cell function is compromised due to immunosuppression, which naturally occurs near calving due to elevated cortisol levels in the cow.
During the later risk period, management practices designed to maximize and supplement the cow’s immune defenses and minimize bacterial challenge from the environment are essential.
Prevention is key
IMI infections during the dry period can have a dramatic impact on the incidence and distribution of mastitis in the next lactation. Subsequent mastitis events that occur during the breeding risk period can have a profound negative effect on fertility. Because mastitis negatively impacts fertility, dairies must make prevention of new IMIs during the dry period a priority. Consult with your herd health veterinarian to create a comprehensive dry cow program.