Infrared thermography or rectal temperature as qualification for targeted metaphylaxis in newly received beef steers and the effects on growth performance, complete blood count, and serum haptoglobin during a 42-day feedlot receiving period*

Objective: The objective was to evaluate rectal temperature and infrared thermography as qualification for targeted metaphylaxis, and effects on clinical health, growth performance, complete blood count, and serum haptoglobin in newly received beef steers during a 42-d feedlot receiving period. Materials and Methods: Crossbred beef steers (n = 240; arrival BW = 258 & PLUSMN; 22.5 kg) were used. Experimental treatments were arranged as a generalized complete block administered to all steers (CONV); targeted metaphylaxis administered to steers with rectal temperature >39.7 & DEG;C (RECT); or targeted metaphylaxis administered to steers with ocular infrared temperature >39.7 & DEG;C (EYE). Body 14, and 42 relative to metaphylaxis.Results and Discussion: Metaphylaxis was adminis- tered to 0% of NCON, 100% of CONV, 48.9% of RECT, and 48.6% of EYE steers (P < 0.01). Therapeutic bovine respiratory disease (BRD) treatment rate did not differ (P = 0.16), although overall BRD treatment rate was mini- mal. Metaphylaxis was 62.5% of total active antimicrobial compound administered to RECT and 32.1% of total ac- tive antimicrobial compound administered to EYE. Both methods of targeted metaphylaxis decreased percentage of animals administered antimicrobials relative to CONV (P < 0.01), but total milligrams of active drug compound administered was not different (P = 0.65). Body weight, DMI, DMI as percentage of BW, and G:F did not differ at any time point (P > 0.07). A tendency (P = 0.06) was observed for ADG from d 0 to 14, where CONV was greatest, RECT and EYE were intermediate, and NCON was least. Day 0 to 42 ADG was greatest in CONV and RECT, least in NCON, and intermediate in EYE (P < 0.01). Platelet count tended (P = 0.10) to be greatest in NCON and RECT, followed by EYE and CONV. No further hematologic treatment differences were observed (P > 0.22).Implications and Applications: Overall BRD mor- bidity was unexpectedly low in the present study. Both methods of targeted metaphylaxis decreased the propor- tion of animals administered antimicrobials relative to conventional metaphylaxis; however, total milligrams of active drug compound administered was not different. The ADG of steers administered targeted metaphylaxis based on rectal temperature did not differ from those ad- ministered conventional metaphylaxis. Use of targeted metaphylaxis with measures of body temperature may decrease the proportion of animals administered metaphy-laxis while maintaining optimal health and growth performance outcomes.