Master of Science / Department of Clinical Sciences / Daniel U. Thomson / Bovine Respiratory Disease (BRD) continues to be one of the largest animal health concerns in the cattle industry. BRD is a multifaceted group of pathogens, both viral and bacterial, that take advantage of an immune compromised calf to cause disease. This study took aim at comparing metaphylactic treatments for BRD in both the feedlot and pasture setting. In the feedlot study, heifers (n=579, 403.7 ± 27.4 lbs) from Southwest Texas were identified as being high risk for BRD and shipped to the Clayton Livestock Research Center in Clayton, NM. Cattle were randomly allocated within truck load lots into 18 to 20 head treatment pens (30 pens; 3 treatments; 10 reps). Cattle were given one of three metaphylactic treatments based on the randomly assigned treatment for their pen within a replicate. The three antibiotic treatments administered at initial processing were: 1) Tulathromycin (2.5 mg/kg), 2) Tilmicosin (13.3 mg/kg), and 3) Gamithromycin (6.0 mg/kg). Cattle were fed a typical commercial starter diet for the first 56-60 d with a step-up ration change at day 28. At the end of the feeding period, pens were weighed and body weights recorded. Dry Matter Intake, morbidity, and mortality were recorded by CLRC personnel daily. Cattle administered tulathromycin had higher daily gains than cattle administered gamithromycin by 0.29 lbs/d (P<.01) and tended (P=0.09) have higher daily gains than cattle that received tilmicosin by 0.18 lbs/d. Tulathromycin treated cattle tended (P = 0.12) to have improved feed efficiency compared to gamithromycin treated cattle. Cattle that received tulathromycin (5.2%) had lower morbidity rates (P < .02) than tilmicosin (14.6%) and gamithromycin (12.79%) treated cattle. There were no treatment differences in dry matter intake or mortality in cattle. For the wheat pasture study, heifers (n=120, 393.2 ± 28.6 lbs) from the same origin and risk were shipped to the CLRC and processed before being trailed to a nearby wheat pasture. Cattle were randomly assigned into three treatment groups (3 treatments, 40 reps), and were given one of three metaphylactic treatments. The three antibiotic treatments administered at initial processing were: 1) Tulathromycin (2.5 mg/kg), 2) Tilmicosin (13.3 mg/kg), and 3) Gamithromycin (6.0 mg/kg). Cattle were allowed to graze on wheat for 54 days with free-choice Hi-Pro mineral mixed with Lasalocid, an ionophore. After 54 days on wheat pasture, the cattle were trailed back to the CLRC facilities and final individual weights were recorded. Morbidity and mortality were recorded daily by CLRC personnel. No differences were identified for ADG (P=0.98), morbidity (P=0.46) or mortality (P=0.36) among the three treatment groups.

Tulathromycin is a macrolide antibiotic approved for use in cattle and swine respiratory disease. Extra-label use of tulathromycin occurs in bison and deer and significant interspecies differences in pharmacokinetics warrant specific investigation in these species. This study involved investigation of the pharmacokinetics of tulathromycin in bison and white-tailed deer following a single 2.5 mg/kg bw subcutaneous injection (n=10) of Draxxin (Pfizer Inc.) to provide important information regarding tulathromycin dosage regimens in these species. As well, tulathromycin distribution and depletion in deer muscle and lung tissues following a 2.5 mg/kg bw subcutaneous injection of Draxxin was investigated to obtain pilot information regarding withdrawal time of tulathromycin in deer. For the pharmacokinetic studies, serial blood samples were collected at baseline and up to 25 days post-injection. Pharmacokinetic parameters were estimated using non-compartmental methods. For the tissue pilot study, deer (n = 2 to 3) were slaughtered at 0, 1, 2, 6, 7, and 8 weeks post-injection. A quantitative analytical liquid chromatography-mass spectrometry method for measuring tulathromycin was developed and validated in bison and deer serum and deer lung and muscle according to international guidelines. Samples were processed by solid-phase extraction. Reverse-phase chromatography was performed by gradient elution. Positive electrospray ionization was used to detect the double charged ion [M+2H]+2 at m/z 403.9 and monitored in selected ion monitoring mode. Tulathromycin demonstrated early maximal serum concentrations, extensive distribution, and slow elimination characteristics in deer and bison. In bison, mean Cmax (195 ng/mL) was lower compared to cattle (300 to 500 ng/mL) and half-life (214 hours) longer (cattle, 90 to 110 hours). In deer, mean Cmax (359 ng/mL) is comparable to cattle, but half-life (281 hours) was much longer. Tissue distribution and clinical efficacy studies are needed in bison to confirm extensive distribution of tulathromycin into lung and the appropriate dosage regimen. Tulathromycin was extensively distributed to deer lung and muscle, with tissue levels peaking within 7 to 14 days after injection. Drug tissue concentrations were detected 56 days after treatment, longer than the established withdrawal time of 44 days in cattle. This prolonged drug concentration in the tissue is supportive for the administration of tulathromycin as a single injection therapy for treatment of respiratory disease of deer. While more study is needed to establish a recommended withdrawal time, the long serum and tissue drug half-life and extensive interindividual variability in tissue levels suggests a withdrawal period well beyond 56 days may be required in deer.