PSVI-27 Evaluation of the D2Dx Immunity Test™ for monitoring castration and arrival stress on immune function in newly received feedlot cattle.

Abstract Castration and arrival stress are recognized as significant immunological challenges in feedlot cattle, particularly in groups not exposed to pre-conditioning protocols. Real-time assessment of immune status during the post-arrival period could provide valuable insight into health outcomes and inform timely management decisions. The D2Dx Immunity Test™, a nanoparticle-based tool that measures the balance between innate and adaptive immunity, can be conducted chute-side at an affordable cost, offering a practical method for immune profiling of high-risk beef cattle. This study aimed to evaluate the utility of the D2Dx test in detecting immunological effects of castration and arrival stress in a commercial feedlot setting. Twenty-five newly received, high-risk beef calves were enrolled and monitored for four weeks post-arrival—typically the highest-risk period for morbidity. All animals underwent standard intake processing, including vaccination, ear tagging, deworming, topical insecticide application, and BVDV testing on day 0. Bulls (CAS; n = 14) were surgically castrated at intake, while steers (STR; n = 11) had been previously castrated and were fully healed at arrival. Weekly body weights were recorded, and blood samples were collected for D2Dx testing on days 0, 7, 14, and 21. Animals treated with antibiotics during the four-week period were classified as sick (S), while untreated animals were classified as healthy (H). Morbidity was 46% in the CAS group and 36% in STR, with mortality rates of 7% and 0%, respectively. Statistical analysis was performed using R (version 4.3.0), with linear mixed-effects modeling via the lmer package. There was no significant main effect of sex (CAS vs. STR) on overall body weight (p = 0.95); however, significant sex-by-time interactions were observed. Steers gained more weight than CAS cattle beginning in Week 2 (p = 0.005), with differences increasing in Weeks 3 and 4 (p < 0.001). These results reflect known post-castration growth suppression and support CAS animals as a relevant comparison group for immune function assessment. A significant main effect of time was observed on D2Dx scores (p = 0.013), with all cattle exhibiting a marked decline between days 0 and 7—indicating a period of immunosuppression likely associated with transport and handling stress. This early drop in immune status highlights a window where D2Dx testing could be used to inform management decisions based on real-time immune profiling. Castration status did not significantly affect D2Dx scores at any time point, though CAS cattle experienced compounded challenges in growth and morbidity outcomes. These findings suggest that the D2Dx Immunity Test™ is a promising, field-ready tool for identifying immunological stress in high-risk feedlot cattle. By integrating immunology into health management, producers may be able to refine interventions, reduce disease incidence, and improve animal welfare outcomes.