Holstein-Friesian heifers (n = 178) from a central Iowa dairy farm were enrolled in a study to determine whether prepartum intramammary treatment of dairy heifers with pirlimycin hydrochloride would reduce the prevalence of intramammary infection (IMI) and lower the somatic cell count (SCC) during early lactation or improve 305-day mature equivalent milk production. Heifers were assigned to treatment and control groups, and treated heifers received a single 50-mg dose of pirlimycin in each mammary quarter approximately 10 days prior to parturition.

Treated heifers had a higher overall cure rate and cure rate for IMI caused by coagulase negative staphylococci (CNS), but postpartum California mastitis test scores and prevalence of chronic IMI did not differ between groups. Mature equivalent 305-day milk production did not differ between treatment groups (trend for higher production when treated, p = 0.085). No pirlimycin residues were detected in postpartum milk samples.