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* University of Guelph, Guelph, Ontario N1G 2W1, Canada
University of Prince Edward Island, Charlottetown, P.E.I. C1A 4P3, Canada
University of Montreal, St. Hyacinthe, Quebec J2S 7C6, Canada
Quality Milk Promotion Services, Cornell University, Ithaca New York 14850-1263, USA
|| Provel, Division of Eli Lilly Canada Inc., Research Park Centre, Guelph, Ontario N1G 4T2 Canada
Corresponding author:
R. T. Dingwell; e-mail:
rdingwell{at}vet.k-state.edu.
The objective of this study was to compare the efficacy of an intramammary infusion, containing tilmicosin phosphate, to an infusion of a negative control intramammary placebo for preventing new intramammary infections (IMI) during the dry period. Cows were enrolled from 24 dairy herds from three geographical regions of Canada. Data from 248 cows and 938 bacteriologically negative quarters at drying-off are summarized. Overall, the rate of new IMI during the dry period was 16.7% of quarters. The new infection rates for quarters that received intramammary tilmicosin compared with the intramammary placebo were 14.4 and 19.4%, respectively. The majority of new IMI was caused by coagulase-negative staphylococci (49%) and environmental streptococcal organisms (26.8%). The probability for quarters to develop new IMI in the dry period was significantly increased when cows had higher milk production before drying-off (P = 0.04), when cows had longer dry periods (P = 0.02), and when dry cows were housed in tie-stall barns (P = 0.002). Higher parity cows and those that had a linear score somatic cell count (SCC) above 4 on the last DHI test were also at increased risk for new IMI (P < 0.10). Administration of intramammary tilmicosin appears to be an efficacious therapy for prevention of new IMI; however, there is currently no approved intramammary formulation of this product available. Use of blanket dry cow antibiotic therapy compared to selective dry cow therapy, as well as the importance of identifying risk factors and managing the environment of dry cows are discussed.
Abbreviation key: CFU = colony forming units, CNS = coagulase-negative staphylococci, DCT = dry cow antibiotic therapy, LS = linear score, OR = odds ratio
Key Words: dry period • mastitis • risk factor • tilmicosin
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