Morphological evaluation of the corpus luteum before embryo transfer is a method commonlyused for the selection of the bovine receptients. The present study evaluated the relation betweenthe corpus luteum and the estrous synchronization protocol on pregnancy rates in recipientsimplanted with in vitro-produced bovine embryos (IVP). 260 crossbred females were selected andsynchronized using two different hormonal protocols: G1 (n=110), with sodium cloprostenol, andG2 (n=150), with norgestomet associated with estradiol benzoate, equine chorionic gonadotrophinand sodium cloprostenol. Corpus luteum (CL) were evaluated on the day of the transfer of theembryos, through rectal palpation, and classified into four types: CL-1 (small), CL-2 (medium), CL-3(large) and CL-4 (enclosed). All transfers were conducted transcervically, in the horn ipsilateral tothe ovary containing the corpus luteum. Pregnancy was confirmed, 30 days after the transfer, byultrasound. The total pregnancy rate was 35,77%, distributed as follows: 17,69% in the recepients withCL-1 (n=46), 30,77% in the recepients with CL-2 (n=80), 43,85% in those with CL-3 (n=114) and 7,69% inrecepients with CL-4 (n=20), resulting in 16 (34,78%), 29 (36,25%), 41 (35,96%) and 7 (35,00%) pregnantfemales, respectively. The results suggest that there is no correlation between corpus luteum sizeand synchronization protocol and the pregnancy rates of bovine recepients implanted with PIVembryos.A avaliação morfológica do corpo lúteo antes da inovulação é um método comumente utilizado na seleção de receptoras bovinas. Objetivou-se verificar a relação entre o protocolo de sincronização de estro e o tamanho de corpo lúteo sobre a taxa de fertilidade em receptoras bovinas inovuladas com embriões produzidos in vitro (PIV). Foram selecionadas 260 fêmeas mestiças e sincronizadas com dois diferentes protocolos hormonais: G1 (n=110), com cloprostenol sódico e G2 (n=150), com norgestomet associado a benzoato de estradiol, gonadotrofina coriônica eqüina e cloprostenol sódico. No dia da inovulação avaliaram-se os corpos lúteos (CL), por palpação retal, sendo classificados em quatro tipos: CL-1 (pequeno), CL-2 (médio), CL-3 (grande) e CL-4 (incluso). As inovulações foram realizadas por via transcervical, no corno ipsilateral ao ovário que continha corpo lúteo. O diagnóstico de gestação foi realizado por ultrassonografia aos 30 dias pós-inovulação. A taxa de fertilidade para os dois tratamentos foi de 35,77%, sendo 17,69% nas receptoras que apresentaram CL-1 (n=46), 30,77% nas que apresentaram CL-2 (n=80), 43,85% nas que apresentaram CL-3 (n=114) e 7,69% nas que apresentaram CL-4 (n=20), resultando em 16 (34,78%), 29 (36,25%), 41 (35,96%) e 7 (35,00%) fêmeas gestantes, respectivamente. Esses resultados sugerem não haver relação entre o tamanho do corpo lúteo e o protocolo de sincronização sobre os índices de prenhez de receptoras bovinas inovuladas com embriões PIV.Influence of the estrus synchronization protocol and the size of the corpus luteum onthe fertility rate in recipients implanted with embryos produced in vitroAbstractMorphological evaluation of the corpus luteum before embryo transfer is a method commonlyused for the selection of the bovine receptients. The present study evaluated the relation betweenthe corpus luteum and the estrous synchronization protocol on pregnancy rates in recipientsimplanted with in vitro-produced bovine embryos (IVP). 260 crossbred females were selected andsynchronized using two different hormonal protocols: G1 (n=110), with sodium cloprostenol, andG2 (n=150), with norgestomet associated with estradiol benzoate, equine chorionic gonadotrophinand sodium cloprostenol. Corpus luteum (CL) were evaluated on the day of the transfer of theembryos, through rectal palpation, and classified into four types: CL-1 (small), CL-2 (medium), CL-3(large) and CL-4 (enclosed). All transfers were conducted transcervically, in the horn ipsilateral tothe ovary containing the corpus luteum. Pregnancy was confirmed, 30 days after the transfer, byultrasound. The total pregnancy rate was 35,77%, distributed as follows: 17,69% in the recepients withCL-1 (n=46), 30,77% in the recepients with CL-2 (n=80), 43,85% in those with CL-3 (n=114) and 7,69% inrecepients with CL-4 (n=20), resulting in 16 (34,78%), 29 (36,25%), 41 (35,96%) and 7 (35,00%) pregnantfemales, respectively. The results suggest that there is no correlation between corpus luteum sizeand synchronization protocol and the pregnancy rates of bovine recepients implanted with PIVembryos.