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Understanding Heifer Mastitis

First lactation heifers are the future of any dairy herd and many producers assume them to be free of intramammary infections when they enter the milking string for the first time.  However, both clinical and subclinical mastitis may affect heifers at calving and may have an impact on milk quality and future performance of these animals.  Over the past decade, mastitis in primiparous animals has been the focus of many studies which have attempted to understand the prevalence, causative pathogens and risk factors responsible.

Prevalence of intramammary infections (IMI) in heifers is highest at calving and decreases during lactation. Studies estimate that between 29 and 75% of quarters are infected pre-partum and 12-45% are infected at calving. Coagulase negative staphylococci (CNS) are the most common pathogens isolated from dairy heifers and generally clear spontaneously. Staphylococcus aureus infections, however, tend to have a much lower spontaneous cure rate.  Other environmental organisms (streptococci and coliforms) have also been found.

Elevated somatic cell counts (SCC) early in lactation (within 14 days of calving) are associated with increased SCC throughout the subsequent lactation and those animals with the highest SCC are at risk for at least one episode of clinical mastitis in their first lactation.  Since mammary growth continues in the first lactation, inflammation may affect development of milk producing tissue.  Multiple authors have found a negative association between SCC in early lactation and total milk production for that lactation.  Those animals with increased SCC and/or clinical mastitis early in lactation have also been found to be at a higher risk for culling than lower SCC heifers.

The likelihood of developing an IMI is not just related to the number and virulence of pathogens to which the animals are exposed. Host-related factors also have an impact on the incidence of mastitis in primiparous animals.  Nutrition affects the incidence of IMI in heifers; both overfeeding and underfeeding were associated with increased clinical mastitis.  Information on mineral and vitamin supplementation and associations with IMI is limited but it had been shown in multiple studies that vitamin E and selenium have a synergistic protective effect on udder health and immune status.  Several studies have investigated the effect of parenteral vaccination of heifers against Staphylococcus aureus.  None of the available bacterins were successful in reducing the prevalence of S. aureus IMI in heifers or in reducing the incidence of clinical or subclinical mastitis but clinical severity and duration of infection appeared to be reduced.  Other environmental factors have also been associated with an increase in SCC in early lactation heifers.  Herds that have higher proportion of older cows with mastitis will have an increased have heifers with higher SCC in early lactation.  Stress also plays a factor: moving heifers to confined housing and using restraints during milking time were associated with increased SCC.  Finally, udder edema increases the risk for IMI in heifers.

Understanding of heifer mastitis, causative agents and risk factors has increased but additional work should be performed to identify management strategies and intervention to decrease prevalence and prevent financial losses to the producer.