Epidemiological Insights Into BVDV and IBRV in Feeder Cattle After Cross‐Regional Transport in China 2022–2024: Coinfection Dynamics and Implications for BRDC Control

Background Bovine viral diarrhea virus (BVDV) and infectious bovine rhinotracheitis virus (IBRV) are key components of the bovine respiratory disease complex (BRDC) in China’s cross‐regional feeder system. We quantified antibody and antigen positivity and identified epidemiological determinants across provinces, seasons, years, and clinical status. Methods We collected 7592 sera and 6651 clinical specimens from five provinces spanning pretransport (north) and posttransport (southwest) settings across all seasons from 2022 to 2024. Seroprevalence and antigen prevalence were summarized by province, year, season, and clinical status. Logistic regression estimated adjusted odds ratios (aORs) for single‐virus outcomes; multinomial models (adjusted relative risk ratios [aRRRs]) and modified Poisson models (adjusted prevalence ratios [aPRs]) evaluated antibody coinfection. Results Overall, 78.85% of sera were BVDV‐antibody positive (95% CI 77.99–79.69) and 70.11% were IBRV‐antibody positive (95% CI 69.07–71.14). Seroprevalence was higher in the southwest (Sichuan/Chongqing) than in the north (Hebei/Inner Mongolia/Liaoning), rose from 2022 to 2024, and peaked in winter; cattle without clinical signs showed higher seroprevalence than symptomatic animals. Antigen positivity was lower overall—BVDV 7.01% (95% CI 6.40–7.65) and IBRV 5.79% (95% CI 5.24–6.38)—and was greater in the southwest and in winter. In multivariable models, BVDV seropositivity was strongly associated with residence in Sichuan (aOR 2.37, 95% CI 1.89–2.99) and Chongqing (aOR 2.86, 95% CI 2.10–3.91) versus Hebei, and with winter (aOR 1.64, 95% CI 1.38–1.96) versus spring; clinical signs were inversely associated (aOR 0.83, 95% CI 0.73–0.95). For antigens, IBRV positivity increased in 2024 vs. 2022 (aOR 1.53, 95% CI 1.16–2.02) and was higher in clinically symptomatic cattle (aOR 1.96, 95% CI 1.54–2.50). Coinfection analyses showed the greatest departure from the double‐negative reference for the BVDV−/IBRV+ category (aRRR 0.500, 95% CI 0.318–0.785; p < 0.01). Conclusions Under China’s cross‐regional finishing model, BVDV/IBRV circulate widely, with higher risk in southwestern provinces, in winter, and in recent years. Antigen detection concentrates among symptomatic cattle, underscoring the value of paired serology—PCR at intake and calendar‐aware vaccination and management before winter moves. These findings support risk‐based BRDC prevention aligned to province and season.