Abstract
Selection for post weaning worm egg count (PWEC) EBV has revealed that lowPWEC sheep have greater resistance to gastrointestinal nematode infection, greater survivability to weaning and generate greater anamnestic response to booster clostridial vaccination. Therefore, it can be hypothesized that selection for PWEC may result in improved generalized immunity. The aim of this study was to compare IgG and IgA antibody concentration in colostrum and milk of Katahdin ewes divergent in their PWEC EBV. Katahdin ewes from the Virginia Tech SWAREC selected for this study had to meet the following criteria: age (3-6 years), have a Katahdin Hair Index EBV (>104, pre-genomic EBV), and be twin bearing. Ewes fitting those criteria were sorted by their PWEC EBV into two groups: lowPWEC (n = 20) with an average EBV of -81 and hiPWEC (n = 18) with an average PWEC EBV of +213. Upon parturition and within 24 hours of lambing, a 20 mL colostrum sample was sterile collected by milking 10 mL from each half of the udder of the ewes, representing the early sample. Milk samples were taken from each ewe at two distinct time points, mid (30-days post-parturition) and late (60-dayd post-parturition) lactation. All samples were placed into pre-labeled 50 mL tubes and frozen on-site. Colostrum and milk samples were thawed and diluted in 36% ammonium sulfate and centrifuged at 3,000 x g for 20 minutes at 4ºC. The removed whey portion was then dialyzed using a 3,000 MW membrane cassette in 1L of PBS (pH 7.4) at 4ºC for 12 hours. Total IgG and IgA from colostrum was measured used an ovine-specific enzyme-linked immunosorbent assay (ELISA). To evaluate IgG and IgA differences, data were analyzed using the General Linear Model (GLM) procedure of SAS with fixed effects of genotype, time, and genotype X time interactions. Means comparisons were performed on LS means of fixed affects or interactions, using Bonferroni adjustment. Main effects of ewe genotype revealed that lowPWEC ewes had greater concentration of both IgG (0.482 vs 0.236 µg/mL; P < 0.001) and IgA (10.5 vs 8.1 µg/mL; P = 0.002) within colostrum. The 2-fold increase of IgG (P < 0.001) within lowPFEC ewe colostrum loses magnitude overtime, nonetheless lowPFEC ewes continue to have greater IgG in milk at mid (0.291 vs 0.183 µg/mL; P = 0.048) and late lactations (0.322 vs 0.183 µg/mL; P = 0.032). These data indicate that lowPWEC Katahdin ewes generate greater colostrum quality as measured by antibody concentration. Therefore, lambs born to these ewes would have a significant advantage in passive immunity from their dams potentially contributing to lamb survivability.