146. Relationship Between Antibody Response to Booster Clostridial Vaccine and Weaning Fecal Egg Counts in Polypay Ewe Lambs

Abstract Previous studies have revealed a relationship between postweaning fecal egg count (PFEC) estimated breeding value (EBV) and antibody production in response to clostridial booster vaccination. While there is value is using the PFEC EBV as a predictor for antibody response, not all breeds and not all sheep submitting data to the National Sheep Improvement Program (NSIP) collect weaning or postweaning FEC. There exists a need to evaluate the relationship between weaning FEC and antibody response to booster vaccination to better assist producers’ selection for disease resistance. Therefore, weaning FEC were collected on 251 summer-born Polypay ewe lambs and analyzed using the modified McMaster FEC technique. One wk after a booster vaccination for clostridial diseases, a serum sample was collected and stored at -20oC. Total immunoglobulin-G (IgG) was measured using the Valita-Titer™ assay that has an IgG detection range of 0-2000 mg/L. Individual serum samples were diluted 1:20 in MOPS buffer then diluted again 1:2 MOPS buffer on the Valita-Titer™ assay plate. After a 15 min incubation at room temperature, plates were analyzed using the fluorescent polarization option on a plate spectrophotometer. Measured IgG concentration was adjusted from sample dilution and converted to mg/ml for reporting. Serum IgG average of the ewe lambs was 41.51 mg/ml with a range of 76.7 – 10.7 mg/ml. Weaning FEC average of the group was 481 eggs/g with a range of 8,900 – 0 eggs/g. Correlation analysis revealed a significant negative correlation between serum IgG and weaning FEC (-0.125, P = 0.045). Ewe lambs were grouped based on the mean IgG concentration ± ½ SD which generate 3 groups; High AB group (n = 70, IgG > 46.9 mg/ml)), Med AB (n = 108, IgG 46.9 – 36.04 mg/ml) and Low AB (n = 76, IgG < 36.04 mg/ml). Analysis of FEC within those groups revealed a significant difference between High and Low groups (334 vs 541 eggs/g; P = 0.04), but the Med group (535 eggs/g) was not different from either High or Low groups. Taken together these data demonstrate a relationship between antibody production to booster clostridial vaccination and parasite resistance. Being able to use a high-throughput test to measure IgG production maybe provide an alternative means to select for parasite resistance and general disease resistance in sheep.