The objective of this study was to explore the seroprevalence of Bovine Viral Diarrhea Virus (BVDV) infection and its associated risk factors in dairy cattle farms near Sebeta town. The overall animal-level seroprevalence of 19.41% observed in this study aligns with previous Ethiopian studies reporting 20.9% seroprevalence across three studies. However, this rate is lower than earlier findings in Ethiopia, who reported 51.7%, 80.82%, and 32.9% seroprevalence rates 39, 42, and 7 in Egypt, who reported 40% rate 37. Conversely, the current seroprevalence is higher than previous reports of 8.4% and 11.46% 43 and 23 in Ethiopia, 10.7% 34 in Sudan and 10.4% 39 in Egypt. The variations in these results might be due to differences in sample size, farm management, hygiene conditions, and distinct agro-ecological zones 18,41. As Ethiopia lacks a BVDV vaccination program, the current findings suggest a natural infection history due to the absence of vaccination efforts.
The observed herd-level seroprevalence of BVDV (Bovine Viral Diarrhea Virus) infection in this study (44.12%) aligns closely with the findings of previous research, such as the 50% seroprevalence reported by Study 3 and corroborated by other studies 41, 33, 18. This consistency suggests a stable prevalence rate in similar environments or under comparable management practices. However, the observed seroprevalence in this study is significantly lower than earlier findings of 95.6% and 69.8% reported from different regions of Ethiopia.40, 3 These discrepancies could be attributed to various factors, including Geographical Variation and temporal changes. Differences in environmental conditions, livestock management practices, and regional disease control measures could contribute to the variability in seroprevalence rates. The regions with higher seroprevalence might have differing ecological factors or higher population densities of susceptible livestock. Over time, the implementation of vaccination programs, changes in herd management practices, or natural fluctuations in disease prevalence could affect seroprevalence7,11.
Analysis of BVDV antibodies in relation to reproductive disorders showed a direct connection between retained fetal membranes and mastitis with BVDV seroprevalence. Dairy cows with a history of retained fetal membranes had a 2.58 times higher risk of seropositivity, corroborating study of 40. Additionally, cows with a history of mastitis had 1.93 times higher odds of being seropositive, which can be attributed to BVDV-induced immunosuppression increasing susceptibility to other infections3.
Moreover, cows without a history of abortion and calf deformity exhibited higher BVDV seropositivity than those with reproductive issues, consistent with other studies reporting higher BVDV antibody prevalence in cows without abortion history 25,3,40. Reproductive problems might be caused by other factors, or cows could clear the BVDV infection before breeding 21,46.
Dairy farms that introduced new animals had twice the likelihood of BVDV infection compared to those with only home-bred cattle, aligning with global reports 43 and 13. The introduction of PI animals likely increases disease prevalence by facilitating virus transmission between infected and non-infected herds 25. Global reports have consistently shown that farms introducing new animals are more susceptible to infectious diseases like BVDV, attributed to the mixing of different herd immunities and potential carrier animals. The presence of PI animals significantly elevates disease prevalence within dairy farms by acting as continuous reservoirs of the BVDV virus, perpetuating its transmission dynamics across susceptible animals. 11,22,18.
A significant association was found between BVDV seroprevalence and various risk factors. Crossbreed dairy cows showed higher seroprevalence compared to local breeds, consistent with previous studies40. This increased susceptibility might be due to crossbreeds' greater vulnerability and potential transmission through artificial insemination22. The observed higher seroprevalence of BVDV in crossbreed dairy cows aligns with established scholar findings indicating their increased susceptibility to infectious diseases, potentially attributed to genetic and physiological differences. Previous studies highlighting the influence of genetic factors on disease susceptibility in dairy cattle support this finding, emphasizing the need for targeted breeding strategies to mitigate disease risks.17,9,3,1 Moreover, the role of artificial insemination as a potential route for BVDV transmission underscores the importance of biosecurity measures in breeding practices to control disease spread within dairy populations.32
Multiparous dairy cattle had 1.3 times higher odds of seropositivity compared to nulliparous cattle, supporting the association of BVDV with reproductive tracts. This aligns with findings from various regions of Ethiopia 38,40,5. The increase in seroprevalence with parity might be due to increased exposure risk or immunotolerance, where animals fail to produce detectable antibodies, supporting the virus's tropism for the reproductive system41.
The study also indicated that larger herds are more susceptible to BVDV infection than smaller herds. Previous research has shown a connection between herd size and BVDV seropositivity 2,3. Larger herds increase contact among cattle, raising virus transmission likelihood 5. The study's observation of increased susceptibility to BVDV infection in larger herds aligns with the previous studies 2,3. This correlation underscores the critical role of herd size in facilitating heightened contact among cattle, thereby amplifying the likelihood of virus transmission5. Understanding these dynamics is crucial for implementing targeted control strategies to mitigate BVDV spread in livestock populations 22.
Additionally, farms with a history of introducing new animals were three times more likely to be infected with BVDV than those with only home-bred animals, consistent with global reports 42,49,16. This may be due to introducing PI animals, dams carrying infected fetuses, or contact between animals from infected and non-infected herds, transmitting the virus to naive herds 36.