Abstract Genetic selection for parasite resistance has been shown to produce beneficial results for ewes and their lamb progeny. Recent literature has also shown that parasite resistance is associated with improved general immune response. The aim of this study was to evaluate differences in colostrum IgG concentrations between parasite resistant St. Croix (STC) and parasite susceptible Suffolk (SUF) ewes. Additionally, this study aimed to determine if supplementation of serum isolated from St. Croix ewes given to Suffolk lambs at birth had the potential to positively impact pre-weaning lamb health. Over 2 years, STC (n = 36) and SUF (n = 34) ewes from the Virginia Tech Sheep Center were managed together through gestation and lactation to evaluate differences in ewe colostrum IgG and lamb production. Within 3 hours of lambing, 20mL of colostrum was collected from ewes, measured utilizing Brix refractometry upon milking, and frozen. Samples were later thawed and diluted with 1X MOPS and refrigerated overnight. Ammonium sulfate (36%) was slowly added and centrifuged at 3,000 x g for 20 minutes at 4 °C. 5mL of whey was removed and added into a cassette dialysis for 12 hours at 4 °C. IgG measurements were obtained using a Valita Titer™ Assay. Following the administration of the pre-lambing vaccinations to ewes (Y1: 7 d, Y2: 14 d), serum was collected and IgG concentrations determined for each ewe, and samples pooled and diluted for each breed. Within three hours of birth, SUF lambs (Y1: n = 16, Y2: n = 33) were given a 1:1 treatment of either SUF or STC serum combined with colostrum milked from their dam. Statistical analyses were performed using PROC GLM in SAS (SAS Institute, Cary, NC). Results showed STC ewes produce significantly higher concentrations of IgG in colostrum as compared to SUF ewes (55.4 vs. 39.5 mg/mL; P 0.01). SUF colostrum IgG concentrations ranged from 18.3 to 68.0 mg/mL. Within the SUF data, ewes with IgG concentrations above average (n = 19) had a significantly higher mean IgG concentration compared to ewes below average (n = 15; 49.1 vs. 27.3 mg/ml; P 0.01). Death losses were recorded in STC and SUF lamb progeny from birth to 60 d of age. In Y1, a pneumonia outbreak affected the lambs before weaning resulting in 44% and 5% death loss in SUF and STC lambs, respectively. Across both years, there were no differences in lamb survivability, body weight, or FEC based on treatment. These results indicate differences in colostrum IgG both between and within breeds. Further research is needed to determine the impact of these differences in lamb progeny performance and health.
Poteat et al. (Wed,) studied this question.