|Clinic:||Kansas State University|
|City, State, ZIP:||Manhattan, KS 66503|
Brad White, DVM, MS
David Amrine, DVM, PhD
Robert Larson, DVM, PhD
Brian Lubbers, DVM, PhD
Kristen Smith, none
1Beef Cattle Institute, Kansas State University, Manhattan, Kansas
2Department of Clinical Sciences, Kansas State University, Manhattan, Kansas
3Student, Department Animal Science, Kansas State University, Manhattan, KS
Judicious and appropriate antimicrobial therapy is a critical topic in beef cattle production. Bovine respiratory disease (BRD) is the most frequent syndrome requiring antimicrobial therapy in post-weaned beef calves; however, little published information has described factors impacting the actual intertreatment interval (ITI) and potential associations of ITI with case outcomes. The objective of this retrospective research is to determine associations between ITI of first and second BRD treatment with antimicrobials with case fatality risk (CFR) and secondarily to identify factors influencing ITI in BRD cases treated at least twice with antimicrobials.
Individual animal feedyard health operational data were collected including cattle treated multiple times for bovine respiratory disease (BRD) from 2014 to 2020. Treatment dates were used to calculate the actual ITI between the first and second treatment for clinical BRD cases treated at least twice with antimicrobials. Metaphylaxis was included as a covariate, but not considered a first treatment for BRD. Data were cleaned removing ITI greater than 100, limiting arrival weights to 400 to 1200 pounds, and eliminating data that included additional gender classifications beyond steer or heifer. The final dataset for analysis consisted of 28,694 individual animal records from 13 feedyards. A multivariable model was created to evaluate potential associations of CFR with metaphylaxis status, ITI category (10-day increments), drug class of the first treatment, gender, number of head received in the group, arrival month, arrival year, and arrival weight. A second multivariable model was created to evaluate potential associations of the arrival and first treatment information with the ITI interval. A random effect was included in all models to account for lack of independence due to observations from the same feedyard.
Multivariable model results indicated ITI was associated with CFR and cattle with shorter ITI had higher CFR compared to cattle with longer ITI. Cattle with ITI of 0-10 days had higher CFR (34.4%± 3.1) than cattle with ITI of 10 to 20 days (27.8%± 2.7) and both were higher than all ITI other categories up to 70 days. Several factors were associated with changes in ITI including drug class of first treatment, arrival month, metaphylaxis status, initial weight and gender. The class of drug was associated with varied differences in ITI (range 16.0 ± 1.9 to 25.4 ± 1.7 days) as different formulations have different durations of activities. Cattle in the 500 to 600 pound range at arrival had the longest ITI (26.0 ± 1.7 days) with shortest ITI in each subsequent category until 800-900 pounds (20.8 ± 1.7 days). Steers had slightly longer ITI than heifers (22.8± vs 21.8± days). The arrival month of the calves also influence ITI with September showing lower ITI (20.3 ± 1.7 days) relative to Jan-July.
The ITI was significantly associated with CFR and understanding this relationship could help influence case prognostication as well as potential modifications to subsequent therapy. Several factors influenced the actual ITI beyond the type of drug administered at first treatment and understanding these factors may help in future treatment protocol design.