Supplement Type Influenced the Immune Response of Nursing Ewes to the Natural Challenge of Gastrointestinal Parasites While Grazing in Woodlands

Abstract Nutritional status influences the immune response of grazing animals to naturally occurring diseases and parasites. Provision of supplementary nutrients may enhance the resiliency of grazing animals to gastrointestinal parasites, which are posing a major health problem in small ruminants raised in Southeastern pastures. Information is limited on the role of supplement type in influencing the immune response of grazing animals to natural health challenges. This study tested the hypothesis that the immune response of nursing ewes to gastrointestinal (GI) parasites would be the same irrespective of the supplement type. The objective of the study was to evaluate the cellular and humoral immune response of nursing ewes naturally infected with GI parasites when supplemented with energy- or protein-rich feeds. Katahdin-St. Croix cross-nursing ewes (n = 18) were divided into two groups. Each group was assigned to separate sets of woodland plots (3 plots/group) and rotated in the respective plots throughout the study period with ad libitum hay from May to August 2022. Group-1 ewes were supplemented with whole corn and Group-2 ewes with whole soybean (0.5% of body weight). Fecal samples and blood samples were collected on days 1, 45, and 70. Fecal samples were analyzed for the type and quantity of GI parasites using the McMaster technique. Blood samples were analyzed for WBC (Total WBC, lymphocytes, neutrophils, monocytes, eosinophils, and basophils) using the Procyte-Dx Analyzer. Enzyme-linked immunosorbent assays were performed on serum samples to quantify immunoglobulins (Ig): IgA, IgG, and IgE. Data were analyzed using GLM Procedure in SAS 9.4. Haemonchus contortus was the major GI parasite affecting ewes. No difference was found between groups for GI parasites, WBC, and IgE. However, IgA and IgG concentrations were less in Group-1 than in Group-2 ewes (P < 0.0001). Overall, the supplement type did not affect the GI-parasite load and the immune response in terms of cellular and IgE. However, the immune response in terms of IgA and IgG was amplified with protein-rich supplements.