RESUMO. Avaliaram-se taxas de prenhez de vacas da raça Nelore das categorias nulíparas, primíparas e multíparas, a partir de dados de quatro estações de inseminações de uma fazenda com sistema extensivo de cria, com pastagens nativas típicas do Pantanal. As probabilidades de ocorrência de prenhez foram calculadas por meio de um modelo que incluiu os efeitos de peso final, escore de condição corporal inicial, escore de condição corporal final e ganho médio diário. As taxas de prenhez foram analisadas pelo teste de qui-quadrado e as análises estatísticas foram realizadas por meio de modelos lineares generalizados, empregando-se a função de distribuição binomial e a função de regressão logística. As taxas de prenhez foram 35,29; 40,98; 74,14 e 52% para as estações de inseminações de respectivamente. As categorias nulíparas, primíparas e multíparas, apresentaram as médias das taxas de prenhez de 84, 43 e 47%, respectivamente. Os efeitos de peso final, escore de condição corporal inicial, escore de condição corporal final e ganho médio diário foram significativos. As probabilidades de prenhez são elevadas com maior peso ao final (exceto para as nulíparas), com maior escore inicial e final e com maior ganho médio diário.Palavras-chave: nulíparas, primíparas, multíparas, taxa de prenhez, inseminação artificial.ABSTRACT. The pregnancy rates of nulliparous, primiparous and multiparous Nellore cows were evaluated from data from four insemination stations at a farm with extensive cow-calf system, based on native pastures typical of the Pantanal. Pregnancy probabilities were calculated by a model that included the effects of final weight, initial and final body condition scores, and average daily daily gain. The pregnancy rates were analyzed by chi-square test and statistical analyses were carried out through generalized linear models, using a binomial distribution function and the logistic regression function. The pregnancy rates were 35.28, 40.98, 74.14 and 52.00% for the 2005/insemination stations, respectively. The nulliparous, primiparous and multiparous categories showed average pregnancy rates of 84, 43 and 47%, respectively. The effects of final weight, body condition score at the beginning of the insemination station, body condition score at the end of the insemination station and daily gain during the insemination station were significant. The probabilities of pregnancy are higher with higher final weight (except for nulliparous cows), with higher initial and final scores and higher average daily gain.

-The objective of this experiment was to evaluate the effects of replacing eCG with FSH or FSH/LH on the diameter of ovulatory follicles (DOF) and the pregnancy rates (PR) of lactating Bos indicus cows subjected to a synchronization of ovulation protocol and fixed-time artificial insemination (FTAI) based on progesterone, estradiol benzoate (EB), PGF2α, and estradiol cypionate (EC). On day 0, primiparous and multiparous Nellore cows (n = 329) at 68 days postpartum were body condition scored (BCS) and received a P4 implant (PRIMER 1.0 g P4) plus 2 mg EB intramuscularly (IM). At day 8, the implant was removed, and 250 μg cloprostenol were injected IM along with 0.5 mg EC. At the time of implant removal, the animals were divided into one of four treatments: cows received (G1) 1 mL of saline solution IM (Control; n = 80); (G2) 300 IU eCG IM (ECG300; n = 84); (G3) 15 mg FSH IM (Folltropin; n = 82); and (G4) 30 IU FSH/LH IM (Pluset; n = 83); all cows were subjected to FTAI 48-54 h after implant removal (day 10). Transrectal ultrasonography was performed to measure the DOF to FTAI and to estimate the pregnancy rate on day 35. A statistical analysis examined the effects of the treatment, technician, semen, BCS, calf age and parity on PR to FTAI. There was no significant difference in PR and DOF among the treatment groups (G1, 41.3%, 13.1 mm; G2, 46.4%, 14.5 mm; G3, 46.3%, 14.2 mm; and G4, 48.2%, 14.3 mm), but PR was higher in multiparous than in primiparous cows. Commercial FSH solutions (Pluset or Folltropin) do not promote increases in PR or DOF of lactating Nellore cows and are equal to eCG in promoting growth in preovulatory follicles and elevating the PR in Nellore cows with a moderate BCS subjected to a progesterone-based FTAI protocol with EC.