SYMPOSIUM - MASTITIS IN DAIRY HEIFERS - MASTITIS IN DAIRY HEIFERS - INITIAL STUDIES ON PREVALENCE AND CONTROL

Initial studies to determine the prevalence of mastitis in heifers of breeding age and in pregnant dairy heifers demonstrated that IMI were present in 97% of heifers and 75% of quarters. The most common isolate s were Staphylococcus aureus, Staphylococcus hyicus, and Staphylococcu s chromogenes; SCC ranged from 12.4 to 17.3 x 10(6)/ml. Approximately 29% of heifers and 15% of quarters exhibited clinical mastitis at bree ding age, as evidenced by clots or flakes in mammary secretions. Histo logic examination of mammary tissues demonstrated significant reductio ns in alveolar epithelial and luminal areas and increases in connectiv e tissue stroma and leukocytosis, illustrating limited development and marked inflammation of infected tissues. A one-time infusion of antib iotic for nonlactating cows into infected quarters greater than or equ al to 45 d prepartum reduced incidence of IMI by 59% at calving compar ed with the pretreatment level; the cure rate for Staph. aureus IMI wa s >90%. Prophylactic treatment of uninfected quarters greater than or equal to 45 d prepartum reduced new Streptococcus sp. IMI by 93%. The mean SCC was 50% lower at calving for treated heifers, and milk yield over the first 2 mo of lactation was 10% greater than that of untreate d controls. Heifers from herds using fly control had a lower prevalenc e of IMI than herds without fly control. Prevalences of IMI and SCC in dairy heifers were higher than previously realized, but mastitis at c alving was controlled by use of therapeutic products for nonlactating cows during pregnancy.