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Ovulation inducers are routinely used in domestic horses, especially when assisted reproduction technologies are applied, with the purpose of modulating hormonal activity. The objective of this study was to evaluate the variation of the sex hormones and the lipid profile of empty and single mares, subjected to the use of medicine regulators of the estrous cycle. We used 30 Mangalarga Marchador mares, aged between three and twelve years which were kept in the municipality of Limoeiro, Pernambuco, Brazil. In the presence of a follicle of ≥ 35 mm in diameter and endometrial oedema grade ≥ 2, the mares were randomly separated into three experimental groups of ten animals each, which were treated with different ovulation inducers: i) G-HCG, 1,000 IU of human chorionic gonadotropin, intravenously; ii) G-Deslo, 1.0 mg deslorelin acetate, intramuscularly; iii) G-Combo, 1.0 mg COMBO®, intramuscularly. All mares were artificially inseminated with chilled semen from one stallion. Blood samples were collected before the experiment and 2, 3, 9, and 15 days after ovulation by jugular venopuncture using vacuum system tubes without an anticoagulant. After centrifugation, serum was separated to measure the concentrations of luteinizing hormone (LH) and progesterone (P4) using an ELISA, and concentrations of triglycerides (TRIG), total cholesterol (COLE), high-density lipoproteins (HDL), and low-density lipoproteins (LDL) were measured using semi-automated equipment. The use of oestrus cycle regulators produced significant variations in P4 and COLE whereas no significant effect was observed on LH, HDL, LDL, TRIG, and total plasma proteins (TPP). This likely resulted from endogenous mobilization required for metabolic adaptations at the onset of gestation, as the reproductive success rate of the three groups indicated that the treatments effectively induced and synchronized ovulation. [ABSTRACT FROM AUTHOR]