PSVI-28 Beyond the bunk: Utilizing D2Dx to assess immune health and inform cattle management in a feedlot system.

Abstract Respiratory diseases such as Bovine Respiratory Disease (BRD) and subsequent co-infections remain leading causes of morbidity and mortality in U.S. feedlots. Early disease detection and proactive intervention are essential, particularly for high-risk cattle. The D2Dx Immunity Test™, a nanoparticle-based assay that evaluates humoral immune activity through interactions with IgG, IgM, and complement C3, has potential as a rapid, chute-side diagnostic tool. This study aimed to evaluate the potential of the D2Dx test as an indicator of immune function in newly received feedlot cattle. We hypothesized an inverse relationship between D2Dx score and body weight, and that castration at intake would negatively influence immune response. Additionally, we expected antibiotic-treated (sick) cattle to exhibit altered D2Dx profiles compared to healthy animals. High-risk beef calves (n = 25) were enrolled and monitored for four weeks post-feedlot arrival. Upon intake (d0), all animals underwent standard processing, including vaccination, deworming, ear tagging, topical insecticide application, and BVDV testing. Bulls (n = 14) were surgically castrated at intake, while steers (n = 11) arrived castrated and fully healed. Body weights were recorded weekly, and whole blood samples were collected on days 0, 7, 14, and 21. Serum samples were analyzed using the Nano Discovery D2Dx Immunity Test procedure. Data were analyzed using R statistical software. Pearson’s correlation analysis revealed a significant negative relationship between D2Dx score and body weight (r = –0.44, p < 0.001). Linear regression indicated that for every 0.01 decrease in D2Dx score, body weight decreased by 39 lbs (β = –3930.09, p < 0.001). This correlation highlights the potential of D2Dx as a marker for immune function during high-risk periods in feedlot cattle. A significant sex-by-time interaction was identified, with steers outperforming bulls in body weight gain post-castration (Week 2: p = 0.005; Week 3: p < 0.001; Week 4: p < 0.001), supporting the impact of castration stress on early performance in the feedlot. Regarding immune function, a significant main effect of time on D2Dx score was observed (p = 0.013), with a notable decrease in immune score during Week 2, likely associated with the stress of feedlot transition and inadvertent wildfire smoke exposure during the 2025 Stillwater fire events. While no main effect of health status on D2Dx score was found overall (p = 0.0761), a significant interaction was observed in Week 2, with sick cattle exhibiting significantly lower D2Dx scores compared to healthy cattle (p = 0.0231), suggesting stress-induced immunosuppression. These findings highlight the D2Dx immunity test’s potential for early identification of immune dysfunction in high-risk feedlot cattle. Future research aims explore the role of environmental stressors, like wildfire smoke, on immune suppression and refine management strategies for improving cattle health and performance.