This study aimed to investigate the effect of Ivermectin (IVM) on the reproductive hormones and hemato-biochemical parameters of twenty apparently healthy ewes weighing 30-40 kg and 2-3 years old. Ewes were randomly divided into two groups (ten for each). The first group was left without treatment (control group), and the second was treated with the recommended therapeutic dose of IVM (0.2 mg/kg, S/C) one day after parturition (treated group). The study continued for three months. Blood samples

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... were collected from the two groups at the 1st, 30th, 60th, and 90th days after IVM treatment. The current study revealed that IVM injection delayed estrous for up to 3 months (absence of estrous signs and no ovarian structures were observed by sonar examination). There was a significant decrease in hemoglobin concentration (Hb), red blood cells (RBCs) count, and packed cell volume (PCV), with a significant increase in total leukocytic count (TLC) at 30th and 60th days post-treatment (p.t.). In addition to a significant decreased at (P<0.05) in the activity of glutathione peroxidase (GSH) and concentrations of total antioxidants (TAC), copper (Cu), phosphorus (P), estradiol, triiodothyronine(T3), and tetraiodothyronine (T4) for up to 3 months. In contrast, a significant increase in concentrations of calcium (Ca), progesterone and cortisol, and activity of malondialdehyde (MDA), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) enzymes were recorded at 30th and 60th days p.t. It has been concluded that IVM delayed estrous in ewes for three months via disturbing the female reproductive hormones and the hemato-biochemical parameters. Therefore, it is recommended that IVM not be injected at least three months before the reproductive season.