2017 ACVIM Forum Research Abstract Program

Clinical signs were poorly correlated with being qPCR negative or qPCR positive for EHV-2, -4, -5. All EHV-1 positive horses were clinical affected. While EHV-2 and EHV-5 were commonly shed, their significance in acute respiratory disease is questionable. EHV-1 or EHV-4 were shed by 3.6% of horses, which could have serious consequences if such animals were introduced into a large mixed population of susceptible horses upon entry into the USA. Foals are immunologically na€ ıve at birth, meaning they have had no exposure to foreign antigens and have therefore not yet mounted any type of protective immune response or accumulated significant levels of immunoglobulins (Ig). Ingestion and absorption of immunoglobulin-rich colostrum are the sole means of passive transfer in foals providing temporary protection from infection for the first few months of life. Current recommendations for optimizing colostral antibody transfer from mares to foals includes vaccination of the mare 4 to 6 weeks prior to parturition. This practice has been recommended to increase the serum antibody level in the dam; therefore the mare would concentrate a higher level of Ig in colostrum during the final two weeks of gestation. Although this management practice is widely accepted, it has not been adequately substantiated using evidenced-based medicine from adequately controlled studies. The purpose of this study was to determine if vaccinating pregnant mares approximately 4 to 6 weeks prior to foaling increases the IgG antibody transferred to foals specific for West Nile Virus (WNV) and Equine Influenza Virus (EIV). Twenty-seven pregnant adult Tennessee Walking Horse (TWH) mares ranging in age from 5 to 23 years were enrolled in the study. All mares were confirmed in foal via rectal palpation and confirmed via ultrasound. Mares were randomized into three treatment groups: G0 na€ ıve control group (no previous vaccinations; no vaccinations administered during the study); G1 vaccinated group (initial 2 vaccination series and revaccinated 4 to 6 weeks prior to foaling); and G2 vaccinated group (initial 2 vaccination series; no pre-foaling revaccination). Mares in G1 and G2 were administered Vetera Ò 4XP + WNV (eastern and western encephalitis, equine influenza clades 1 and 2 + WNV) labeled safe for use in pregnant mares. Following parturition, blood was collected and processed from each foal to determine IgG levels (passive immunity) and serum aliquots frozen at À80°C. Serum was shipped to Gluck Equine Research Center, Lexington, KY for measurement of serum hemagglutination-inhibiting (HI) equine influenza virus antibody levels against Kentucky/14 (Florida clade 1) and Ayrshire/13 (Florida clade 2) reference strains and samples were shipped to Cornell Animal Health Diagnostic Center, Ithaca, NY for analysis of WNV IgG antibody levels measured by ELISA. The mean antibody level was reported accompanied by standard deviation and 95% confidence intervals. Serological titer values below the quantifiable limit were reported as '< 10' and the value of 5 was substituted for these analyses, which provided a conservative estimate. The null hypothesis there was no vaccination effect was tested with a mixed model repeated measures methodology with subject as a random effect. All pairwise comparisons were reported between vaccination groups. Models were run separately for each reference strain. P values < 0.05 were considered statistically significant.