PSI-13 - Effect of Targeted Metaphylaxis Using Blood Leukocyte Status on Health, Performance, and Economic Outcomes of Auction-derived Feedlot Heifers

Abstract: The study objective was to evaluate health, performance, and antimicrobial costs of heifers where targeted metaphylaxis was guided by a commercial blood leukocyte analyzer compared to a traditional metaphylaxis regimen. Using a randomized complete block design, heifers (n=1,271; initial body weight (BW) = 233.3±1.08 kg) were randomly allocated to treatment pens (n=20; 10 blocks). Treatments were: 1) cattle administered metaphylactic treatment with gamithromycin at arrival (META), and 2) cattle administered metaphylaxis with gamithromycin according to the blood leukocyte analyzer outcome (TARGETED). The blood leukocyte analyzer indicated immune status of individual animals according to the number and proportion of different leukocytes in the blood; red signified “abnormal” and green signified “normal” status. Only cattle with a red outcome were administered antimicrobial in the TARGETED treatment. Of all cattle enrolled in the study, 73% were deemed normal and 27% were deemed abnormal by the chute side blood analyzer. Treatment groups had an equal distribution of normal (META = 73% TARGETED = 74%) and abnormal (META = 28% TARGETED = 26%) cattle enrolled in the study. Cattle were fed a common starter ration for the duration of the 62-d study. Pen riders were blinded to treatment pen status. Data was analyzed using PROC MIXED and GLIMMIX in SAS. Final BW, ADG, and feed conversion were less for TARGETED (P≤0.02). However, the arrival processing antimicrobial cost (META = 11.77 and TARGETED = $3.27/heifer) and total antimicrobial cost (META = 17.77 and TARGETED = $9.12/heifer) was reduced (P< 0.01) for TARGETED. TARGETED had an arrival processing antimicrobial cost savings of $8.50/heifer and an overall drug input cost savings of $8.65/heifer. The BRD morbidity rate for normal status heifers was 18.85% and more than abnormal (26.49%; P< 0.01). Normal status heifers had a mortality rate of 3.17 vs. 5.80% for abnormal (P=0.03). In conclusion, drug costs were reduced but performance of TARGETED was also less.