ABSTRACT: In ruminants, the period from fertilization to implantation is relatively prolonged, and survival of embryos depends on uterine secretions, or histotroph. Our objective was to determine if prebreeding diet affected histotroph proteome in beef cattle. Cows were assigned to 1 of 4 diets: control (CON), high protein (PROT), high fat (OIL), or high protein and fat (PROT+OIL). After 185d on diets, an intravaginal progesterone implant (CIDR) was inserted for 7 days. At 9 days post CIDR removal, animals with a corpus luteum were selected (n = 16, 4/treatment). Proteins were isolated from histotroph collected by uterine lavage and analyzed with LC-MS/MS. Over 2000 proteins were expressed (n >= 3 cows/treatment), with 1239 proteins common among every group. There were 20, 37, 85, and 123 proteins unique to CON, PROT+OIL, PROT, and OIL, respectively. Relative to CON, 23, 14, and 51 proteins were differentially expressed in PROT+OIL, PROT, and OIL, respectively. Functional analysis found that 53% of histotroph proteins were categorized as extracellular exosome, 3.28% as cell-cell adhesion, and 17.4% in KEGG metabolic pathways. Differences in proteomes among treatments support that prebreeding diet affects histotroph. Understanding the impact of diet on histotroph proteins may help to improve conception rates.