Reducing the incidence of intramammary infection in heifers by using prepartum systemic tylosin therapy: initial results of a single herd pilot study

Background: mastitis in heifers is recognized as an important problem that impacts animal health and wellbeing and reduces milk quality and lifetime productivity. Objective: to assess the effectiveness of intramuscular administration of tylosin (20 g) as a method to prevent and treat intramammary infections (IMI) in heifers. Methods: heifers from a commercial farm in Michigan, due to calve within 14 to 18 d, were assigned randomly to one of two treatment groups. The control group (n=108 heifers) received no antibiotic treatment or teat sealants to prevent IMI. The tylosin group (n=112 heifers) was injected intramuscularly with 20 g of tylosin. Quarter milk samples were taken in duplicate for bacterial culture from all functional quarters at 2 to 6 d (sample 1) and 7 to 15 d (sample 2) after calving. Representative isolates from sample 1 were speciated. Somatic cell counts and milk production were recorded. Results: in sample 1, 42% of the heifers, and 16.5% of the quarters were infected. Coagulase-negative staphylococci (CNS) and streptococci infected 10.8% and 3.6% of the quarters, respectively. No antibiotic residues were detected at either sample 1 or sample 2. No differences were observed in Somatic Cell Count (SCC) and milk production between tylosin treated animals and controls, however, uninfected heifers had a lower somatic cell score (SCS). At the heifer level, tylosin did not reduce significantly IMI infection rate caused by Gram-positive bacteria. At the quarter level, tylosin reduced levels of IMI caused by CNS. Conclusion: tylosin administration to primigravid heifers 2 weeks before expected calving should not be advised without first evaluating udder health, management and economic implications on each individual dairy farm should be taken into account