JAVMA, Vol 235, No. 3, August 1, 2009 Scientific Reports 299 RUMINANTS/ SWINE/CAMELIDS I njectable antimicrobials are used to treat individual pigs with bacterial infections. However, with large herd sizes, labor constraints, and the ability of some pathogens to spread quickly within a herd, swine pro- ducers must rely on other therapeutic approaches to treat groups of pigs, and oral administration of anti- microbials through drinking water is a common strat- egy. Medication of drinking water minimizes labor re- quirements and can be used to metaphylactically treat large groups of pigs. Farm personnel prefer to use medicated drinking water because of the relative ease of administration and safety (eg, avoidance of broken needles in the bodies of pigs), compared with inject- able antimicrobials. The degree of absorption of various orally admin- istered antimicrobials is highly variable. In animals, the gastrointestinal system readily absorbs some antimicro- bials such as tiamulin, and substantial blood concentra- Water-flow variation and pharmacoepidemiology of tetracycline hydrochloride administration via drinking water in swine finishing farms Paul M. Dorr, DVM, PhD; Megan S. Nemechek, BS; Alan B. Scheidt, DVM, MS; Ronald E. Baynes, DVM, PhD; Wondwossen A. Gebreyes, DVM, PhD, DACVPM; Glen W. Almond, DVM, PhD Objective—To evaluate variation of drinking-water flow rates in swine finishing barns and the relationship between drinker flow rate and plasma tetracycline concentrations in pigs housed in different pens. Design—Cross-sectional (phase 1) and cohort (phase 2) studies. Sample Population—13 swine finishing farms (100 barns with 7,122 drinkers) in phase 1 and 100 finishing-stage pigs on 2 finishing farms (1 barn/farm) in phase 2. Procedures—In phase 1, farms were evaluated for water-flow variation, taking into account the following variables: position of drinkers within the barn, type of drinker (swing or mount- ed), pig medication status, existence of designated sick pen, and existence of leakage from the waterline. In phase 2, blood samples were collected from 50 pigs/barn (40 healthy and 10 sick pigs) in 2 farms at 0, 4, 8, 24, 48, and 72 hours after initiation of water-administered tetracycline HCl (estimated dosage, 22 mg/kg [10 mg/lb]). Plasma tetracycline concentra- tions were measured via ultraperformance liquid chromatography. Results—Mean farm drinker flow rates ranged from 1.44 to 2.77 L/min. Significant differ- ences in flow rates existed according to drinker type and whether tetracycline was included in the water. Mean drinker flow rates and plasma tetracycline concentrations were signifi- cantly different between the 2 farms but were not different between healthy and sick pigs. The plasma tetracycline concentrations were typically < 0.3 µg/mL. Conclusions and Clinical Relevance—Many factors affected drinker flow rates and therefore the amount of medication pigs might have received. Medication of pigs with tetracycline through water as performed in this study had questionable therapeutic value. (J Am Vet Med Assoc 2009;235:299–304) tions are achieved within a few hours. 1 In contrast, oth- er antimicrobials such as spectinomycin and neomycin are poorly absorbed. The tetracyclines (oxytetracycline, tetracycline, and chlortetracycline) are widely used to medicate drinking water; however, in grower-finisher pigs, the bioavailability or amount of active compound that enters circulation is lower after oral administration than after IV administration. 2,3 In pigs, IV or IM admin- istration of antimicrobials yields greater, more rapid in- creases in blood concentrations of antimicrobials than does medication of drinking water. 3 Mass treatment of pigs in integrated swine pro- duction systems requires the administration of medi- From Research and Development, Merial Limited, 3239 Satellite Blvd, Duluth, GA 30096 (Dorr); the Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606 (Nemechek, Baynes, Almond); Swine Veteri- nary Services, Pfizer Animal Health, 1883 Flat Rock Church Rd, Louisburg, NC 27549 (Scheidt); and the Department of Veterinary Preventa- tive Medicine, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210 (Gebreyes). Dr. Dorr’s work was supported by funds from private agricultural industry and Pfizer Animal Health. Presented in part at the 39th Annual Meeting of the American Association of Swine Veterinarians, San Diego, March 2008. The authors thank Beth Barlow, Jessica Clark, Justin Cleary, Holly Hinson, Bryna Riley, Rebecca Robbins, Patty Routh, and Rita Sabadish for sample collection and laboratory work. Address correspondence to Dr. Dorr. ABBREVIATION UPLC Ultraperformance liquid chromatography