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ABSTRACT. Grillo G.F., Guimarães A.L.L., Couto S.R.B., Abidu-Figueiredo M. & Palhano H.B. [Comparison of pregnancy rate between heifers, primiparous and multiparous Nellore submitted to artificial insemination fixed time.] Comparação da taxa de prenhez entre novilhas, primíparas e múltíparas da raça Nelore submetidas à inseminação artificial em tempo fixo. Revista Brasileira de Medicina Veterinária, 37(3):193-197, 2015. Departamento de Biologia Animal, Universidade Federal Rural do Rio de Janeiro, Rodovia BR 465, Km 7, Seropédica, RJ 23890-000, Brasil. Email: email@example.com The aim of this study was evaluate the reproductive performance of cows from Nelore in a program fixed time artificial insemination (TAI) pregnancy rates by comparing the categories of heifers, primiparous and multiparous. For the experiment, we used the Nellore females belonging to the same herd on property located in the coastal lowlands of the state of Rio de Janeiro, kept on pasture divided into three groups and submitted to the same synchronization protocol for TAI (D0- 2,0 mg of estradiol benzoate + bovine intravaginal device with 1.0g progesterone, D8- implant removal + 250μg of cloprostenol + 300 IU eCG, D9- 1.0 mg.of Bz. estradiol, D10- IATF). The groups were divided according to rank, in group I, n=150 heifers, group II, n=150 primiparous group III, n=181 multiparous all with body condition score (BCS with 1-5 scale) ≥ 2,0. The overall pregnancy rate was 86% (129:150), 45.3% (41:150) and 76.8% (139:181) to groups I, II and III, respectively. Data were analyzed by chi-square test and the results indicated a statistically significant difference (P <0.05) between groups I and II and between groups II and III, with no difference between groups I and III. Therefore it was concluded that primiparous Nellore cows, showed poor reproductive performance in TAI program used when you compare to heifers and multiparous of the same race, which affected the reproductive efficiency of the herd studied.