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Comparison of the host immune response to the footrot pathogenic bacteria in different genotypes of Katahdin sheep
Polymorphism at the DQA2 and DQA2-like loci located within the Major Histocompatibility Complex (MHC) was utilized to develop gene marker screening test to identify resistant vs. susceptible genotype for Katahdin ewes. The objective of this study was to compare the host immune response by IgG to Dichelobacter nodosus in footrot resistant vs. susceptible genotype for sheep. Fifty four Katahdin ewes, 18 in each of high resistant footrot gene markers (HR), medium resistance (MR) and low resistance (LR) were selected. Ewes were divided into control and treatment groups. Cultures of D. nodosus were inoculated to the inter-digital skin of the treatment group and held there with bandages for 7 days. Blood samples were collected for 5 weeks to measure the immune response. The blood collected in a vacutainer (10 ml) from the jugular vein of sheep in both control and treatment groups during footrot pathogenic challenge was centrifuged at 2000 RPM for 5 min to separate the serum. The IgG level (mg/ml) was measured by using an Enzyme-linked immunosorbent assay (ELISA) kit (GenWay, Biotech, Inc.). The data were analyzed by using mixed model procedures of SAS and P < 0.05 was considered as significant. The IgG level in sera (mg/ml) was not different (P = 0.45) among different marker groups, and between the beginning and the end of trial (P > 0.05). The IgG level in sera of both treatment and control groups was in the normal range (7.6-40 mg/ml), however; it was greater in treatment than control group (P< 0.0001). Since no active infection happened in animals, the IgG level in sera remained in the normal range in both control and treatment groups and the higher level of IgG in treatment group might be due to bacteria inoculation or higher stress perception.
Keywords:
Footrot, Sheep, Genotype