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 isolates were Staphylococcus aureus, Staphylococcus hyicus, and Staphylococcus chrornogenes; SCC ranged from 12.4 to 17.3 X 10(6)/ml. Approximately 29% of heifers and 15% of quarters exhibited clinical mastitis at breeding age, as evidenced by clots or flakes in mammary secretions. Histologic examination of mammary tissues demonstrated significant reductions in alveolar epithelial and luminal areas and increases in connective tissue stroma and leukocytosis, illustrating limited development and marked inflammation of infected tissues. A one-time infusion of antibiotic for nonlactating cows into infected quarters 245 d prepartum reduced incidence of IMI by 59% at calving compared with the pretreatment level; the cure rate for Staph. aureus IMI was 90%. Prophylactic treatment of uninfected quarters 245 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 untreated controls. Heifers from herds using fly control had a lower prevalence of IMI than herds without fly control. Prevalences of IMI and SCC in dairy heifers were higher than previously realized, but mastitis at calving was controlled by sue of therapeutic products for nonlactating cows during pregnancy