149. Relationship Between Immune Fitness and Maternal Productivity Traits in Katahdin Sheep

Abstract Antibody response to vaccination may be used to quantify immune fitness. Understanding relationships between immune fitness and maternal productivity traits is necessary to optimize breeding objectives. The objective here was to evaluate antibody concentration post-Clostridium perfringens Type C&D and C. tetani (CDT) vaccination relative to maternal traits in Katahdin sheep. Purebred Katahdin sheep from the Upper Piedmont Research Station (UPRS; Reidsville, NC; n = 46) and North Carolina State University Small Ruminant Education Unit (SREU; Raleigh, NC; n = 39) were born mid-February to early March 2024. Lambs were given an initial CDT vaccination on April 4 (UPRS) and April 24 (SREU) followed by booster on April 24 (UPRS) and May 13 (SREU). Serum was collected seven days post-booster vaccination for IgG antibody concentration analysis via the Valita Titer assay. All lambs were enrolled in National Sheep Improvement Program (NSIP) with phenotypes submitted for growth, maternal, and fecal egg count traits. Maternal estimated breeding values (EBVs) including weaning weight (WWT), maternal weaning weight (MWWT), number of lambs born (NLB), number of lambs weaned (NLW), and Maternal Hair Index were summarized from September 2025 data run. A subset (n = 26) of 2024 spring-born ewe lambs were exposed for breeding in April 2025. Pregnancy status in these yearling ewes was assessed by ultrasound 38 days after ram removal (June 23). Effects of location (UPRS vs. SREU), birth and rear type, and sex on IgG status were analyzed with SAS (9.4) along with relationships between IgG response to vaccination and maternal EBVs. A post-hoc analysis of IgG concentration based on pregnancy status was performed to evaluate effects of response to vaccination as lambs on fertility as yearling ewes. There were no effects of litter size, sex, nor birth location (P > 0.05). No correlations existed between IgG concentration and WWT, MWWT, NLB, NLW nor Maternal Hair Index EBVs (R2 = 0.003, 0.008, 0.001, 0.004 and 0.002; respectively). Yearling ewes confirmed pregnant had lower IgG concentrations compared to open ewes (P < 0.05). These data indicate response to vaccination measured by IgG concentration one week post-booster injection is likely independent from genetic potential for many ewe productivity traits. However, no EBV is available for fertility. The ability to mount a greater immune response to vaccination is potentially an indicator of decreased ability to establish a pregnancy. Thus, additional investigation is needed to explore the relationship between response to vaccination and pregnancy outcomes.