PSXI-16 Intercaruncular lipidome is affected by form of Se at maternal recognition of pregnancy in beef heifers.

Abstract Southeastern regions of the United States have soils and consequently forages that have inadequate concentrations of selenium (Se), necessitating supplementation of this trace mineral to the diet of grazing cattle. Supplementation conventionally occurs using an inorganic form of selenium (ISe), however organic forms (OSe) are available when cattle naturally consume forage. We have studied the effects of supplementing a 1:1 combination of ISe:OSe (MIX) versus the industry standard of ISe alone, and observed significant effects on the corpus luteum (CL), endometrium, and systemic blood chemistry, culminating in a MIX-induced increase in length of the conceptus at maternal recognition of pregnancy (MRP). Herein we aimed to determine the effect of supplementation with MIX versus ISe on the lipidome of intercaruncular endometrial (ICAR) tissues of beef heifers at MRP to identify mechanisms supporting the MIX-induced increase in conceptus length. Angus-cross heifers received no Se for 45 days (Se depletion) followed by ISe alone for 45 days (Se repletion). Heifers were then assigned to receive at least 90 days of supplementation with either ISe (n = 6) or MIX (n = 6) prior to synchronization of estrus and artificial insemination. On d17 of presumed pregnancy (MRP), heifers were killed, and reproductive tracts collected. Specifically, ICAR samples were collected using an 8 mm biopsy punch for an untargeted C30 lipidomic analysis. Thermo Scientific LipidSearch software version 5.1.8 was used for lipid identification and sample alignment. Multivariate analysis was performed using MetaboAnalyst6.0. A total of 879 lipid ions were identified using positive ion mode with the top five classes being triglycerides (27%), phosphatidylcholine (24%), ceramide (9%), diglyceride (8%), and sphingomyelin (7%). A total of 167 lipid ions were identified using negative ion mode with the top five lipid classes being fatty acids (43%), sphingomyelin (26%), lysobisphosphatidic acid (11%), lysophosphatidylcholine (10%), and phosphatidylserine (6%). We identified 21 and 7 significantly affected lipids in positive and negative ion mode, respectively. Of these, the concentration of key fatty acids important for development of the preimplantation embryo (arachidonic, behenic, docosahexaenoic, linoleic, and oleic acids) were significantly less abundant in ICAR from MIX compared to ISe heifers (P < 0.05). This was also associated with a less abundant concentration (P < 0.05) of acylcarnitines, phosphatidylcholines, and triglycerides that store these fatty acids. It appears that the form of supplemental Se provided to achieve a Se-adequate status is altering the composition of lipids, particularly fatty acids, which are directly related to the concentration of these in the histotroph to nourish the post-hatching, pre-implantation conceptus. The differences observed in the relative concentration of these fatty acids in the ICAR between ISe and MIX-treated heifers may reflect a reduced requirement by the more developed MIX-treated conceptus at MRP.