hetacillin and Mastitis--Bovine

Mastitis remains a critical disease in the dairy industry and the use of intramammary antibiotics plays a critical role in mastitis treatment. Hetacillin is currently approved as an intramammary antibiotic that is used to treat mastitis in dairy cows. It is approved for once a day administration and can be used for a total of 3 d. An increasing number of dairy farms are milking 3 times per day (instead of the traditional 2 times per day) and very little pharmacokinetic data exists on the use of intramammary drugs in a 3×system. The primary purpose of this study was to determine if once a day intramammary infusion of hetacillin is sufficient to maintain therapeutic drug concentrations in cattle milked 3 times per day. Eight Holstein cattle milked 3 times per day were used in this study. After collecting a baseline milk sample, each cow received intramammary infusions of hetacillin in the left front and right rear quarters once a day for 3 d. Milk samples from each of the treated quarters were collected at each milking and frozen until analysis. Milk samples were analyzed for ampicillin concentrations using an ultra-performance liquid chromatography method. All treated quarters had antibiotic concentrations well above the minimum inhibitory concentration (MIC) for gram-positive mastitis pathogens at 8 and 16 h postinfusion. Milk concentrations had fallen well below the MIC by the 24-h period (before the next infusion). All 8 cows in this study consistently had individual quarter milk ampicillin concentrations below the FDA tolerance of 0.01 μg/mL (10 ppb) within 48 h of the last infusion. Based on this study, milk ampicillin concentrations exceed the minimum inhibitory concentration required to inhibit the growth of 90% of organisms (MIC90) for at least 65% of the dosing interval, which is sufficient for once-daily dosing with most cases of gram-positive mastitis. Therefore, intramammary hetacillin should be an effective treatment for the vast majority of gram-positive mastitis pathogens when used according to label (once per day) in cows milked 3 times per day.

Topics: Ampicillin; Animals; Anti-Bacterial Agents; Cattle; Dairying; Female; Lactation; Mammary Glands, Animal; Mastitis, Bovine; Microbial Sensitivity Tests; Milk; Penicillins

Antimicrobials are frequently used for treatment of bovine mastitis and few studies have examined modern treatment strategies on large US dairy farms. The objective of this study was to describe treatment practices for clinical mastitis occurring in cows on large dairy herds in Wisconsin. Treatments performed on 747 cows experiencing cases of mild, moderate, or severe symptoms of clinical mastitis were recorded on 51 Wisconsin dairy farms. Duplicate milk samples were collected from the affected quarter for microbiological analysis at the onset of clinical mastitis and 14 to 21 d after treatment ended. Cows were treated according to individual farm protocol. Drugs and doses used for treatments were recorded for each case. Among all herds, 5 intramammary (IMM) antimicrobials (amoxicillin, hetacillin, pirlimycin, ceftiofur, and cephapirin) were used to treat cows for clinical mastitis. Of 712 cows with complete treatment data, 71.6% were treated with IMM ceftiofur either solely or combined with other antimicrobials (administered either IMM or systemically). Of cows experiencing severe symptoms of clinical mastitis, 43.8% received IMM treatment concurrent with systemic antimicrobials. Of all cows treated, 23.1% received an additional secondary treatment (either IMM, systemic, or both) because of perceived lack of response to the initial treatment. The majority of IMM treatments were administered to cows with a microbiological diagnosis of no growth (34.9%) or Escherichia coli (27.2%). Half of the cows experiencing cases caused by E. coli were treated using systemic antimicrobials in contrast to only 6.8% of cows experiencing cases caused by coagulase-negative staphylococci. In conflict with FDA regulations, which do not allow extra-label treatments using sulfonamides, a total of 22 cows from 8 farms were treated with systemic sulfadimethoxine either solely or in combination with oxytetracycline. Antimicrobial drugs were used on all herds and many cows received extra-label treatments. Great opportunity exists to improve mastitis therapy on large dairy herds, but use of more diagnostic methodologies is necessary to guide treatments. Farmers and veterinarians should work together to create protocols based on the herd needs considering reduced inappropriate and excessive use of antimicrobials.

Topics: Amoxicillin; Animals; Anti-Bacterial Agents; Cattle; Cephalosporins; Cephapirin; Clindamycin; Escherichia coli; Female; Klebsiella; Logistic Models; Mammary Glands, Animal; Mastitis, Bovine; Oxytetracycline; Pasteurella; Penicillins; Staphylococcus; Streptococcus; Wisconsin

The effect of intramammary antibiotic therapy at calving on mastitis infection prevalence, linear score milk somatic cell count, and milk NAGase activity, 30 d postpartum, and on milk production, 90 to 120 d postpartum, was tested. Cows (n = 175) were split into treatment and control groups at drying off. All cows received commercial dry cow therapy. At calving, treated cows received commercial lactating cow therapy in all quarters after the first two milkings; control cows were not treated. Composite milk samples were aseptically collected from all cows at drying off, calving, and 30 d postpartum. Udder health traits: linear score milk SCC, NAGase activity, and bacterial content in milk, were determined on all samples. The first three DHI milk weights were recorded for all cows. Treatment and control cows had similar prevalences of intramammary infections during the dry and 30-d postpartum periods. Least squares means of linear score milk SCC and NAGase activities were similar at drying off and calving. Cell count scores were similar between groups; NAGase activities were higher in control cows at 30 d postpartum. Control cows tended to produce more milk postpartum. Results demonstrated no advantage of intramammary therapy at calving in improving milk production or udder health.

Topics: Acetylglucosaminidase; Animals; Cattle; Dihydrostreptomycin Sulfate; Female; Mastitis, Bovine; Milk; Penicillins; Postpartum Period; Pregnancy