PSII-A-6 - Evaluation of Maternal Plane of Nutrition and Selenium Supplementation on the Neonatal Fragment Crystallizable Receptor (FcRn) in Ewe Mammary Tissue

Abstract: Maternal immunoglobulin G (IgG) in livestock species is transferred to the offspring exclusively through colostrum. In ruminants, a highly selective mammary barrier allows only immunoglobulin G1 to enter colostrum in substantial amounts. The neonatal fragment crystallizable receptor (FcRn) is responsible for the bidirectional transport of IgG; however, its role in concentrating IgG into colostrum is not well described. The objective of this study was to evaluate maternal nutrition and supranutritional selenium (Se) supplementation on FcRn abundance in mammary tissue. Pregnant Rambouillet ewes (n = 80) were used in a 2 x 3 factorial treatment arrangement which included the main effects of dietary Se [adequate Se (9.5 µg/kg of BW) vs. high Se (81.8 µg/kg of BW)] and plane of nutrition [60%, 100%, and 140% of requirements]. After parturition, ewe mammary glands were collected, and tissue samples were fixed in 10% NBF before paraffin embedding and sectioning. Cross-sections (5 μm) were mounted onto glass slides, deparaffinized, stained for FcRn, and counterstained with DAPI. Areas of tissue cross-sections were captured with Plan-Apochromat 20x/0.8 NA lens using the tiling module of Zeiss software. Images were analyzed using ImagePro Premiere software. Relative fluorescence within the areas of interest was used as an indicator of FcRn abundance with data presented as receptor abundance per glandular tissue area. Data were analyzed using the general linear model procedure of SAS. High Se supplementation increased FcRn abundance per glandular area (P = 0.01). Abundance of mammary FcRn was not influenced by maternal plane of nutrition. Mammary FcRn was positively correlated (r² = 0.25; P = 0.02) with IgG concentration in colostrum. Results indicate the presence of FcRn in ewe mammary tissue and correlation with colostral IgG. Further evaluation of the role of supranutritional Se and the FcRn is needed.