Objective—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.
Design—Prospective clinical trial.
Animals—183 Holstein-Friesian heifers (663 quarters)
from 2 dairy farms.
Procedure—Heifers were assigned to treatment and
control groups. Treated heifers received a single 50-mg
dose of pirlimycin in each mammary quarter approximately
10 to 14 days prior to parturition. Prepartum
mammary gland secretions and postpartum milk samples
were collected for bacterial culture. Postpartum
milk samples were also collected for determination of
SCC or California mastitis testing and were tested for
pirlimycin residues. Mature equivalent 305-day milk
production data were recorded.
Results—Treated heifers in herd A had a higher overall
cure rate, higher cure rates for IMI caused by coagulase-negative staphylococci (CNS) and Staphylococcus
aureus, lower SCC, and lower prevalence of chronic
IMI, compared with control heifers. Treated heifers in
herd B had a higher overall cure rate and cure rate for
IMI caused by CNS, compared with control heifers, 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 herds or treatment groups. No pirlimycin
residues were detected in postpartum milk samples.
Conclusions and Clinical Relevance—Results suggest
that prepartum treatment of dairy heifers with pirlimycin
may reduce the prevalence of early lactation
IMI, particularly IMI caused by CNS, without causing
pirlimycin residues in milk. (J Am Vet Med Assoc 2005;227:1969–1974)