PARENT SESSION
REPRODUCTIVE TECHNOLOGIES

Wednesday, August 4, 2004
10:30 AM–12:30 PM
Buchanan Courtyard

(622) STAGE OF DEVELOPMENT AFFECTS THE SEX RATIO OF BOVINE EMBRYOS PRODUCED IN VITRO.

Calegari, Renata¹, Martins, Jr., Alicio¹, Canellas, Luis Fernando¹, Rodrigues, Eduardo Augusto¹, Paschoal, Daniela¹, Barbieri, Fausto¹, ¹ Department of Clinical Surgery and Animal Reproduction, College of Veterinary Medicine, University of São Paulo State, Araçatuba, SP, Brazil

ABSTRACT- Various factors influence the rate of development and sex ratio of bovine embryos produced in vitro. The mechanisms envolved are not clear, however it may induced by in vitro culture conditions originating before or after fertilization. The aim of this study was to determine the effects of stage of development of Day 7 in vitro-derived bovine embryos on the percentage of males and females fetuses. Embryos were morphologically evaluated under a stereoscope (x 70) and divided by developmental stage in 4 groups: morula (M), early blastocyst (EB), blastocyst (B), and expanded blastocyst (ExB). Cross-bred recipients were induced to come into estrus with prostaglandin. On Day 6, 7 or 8 following the onset of estrus, 7-day old embryos were randomly transferred nonsurgically into the horn ipsilateral to the corpus luteum. First pregnancy diagnosis and fetal sexing were determined by ultrasound using a B-mode scanner (Pie Medical 200) connected to a 6 MHz linear-array transducer around Day 30 and 60, respectively. Differences between proportions were compared by Chi-square analysis with p<0.05 taken as significant. At the time of sex determination the number of pregnant recipients dropped from 164 to 151 (92.1%), with an early embryonic and/or fetal loss of 7.9% (13/164). Thus, a total of 151 pregnant recipients were used for fetal sexing. The overall male percentage (48.7%) was not different from female (43.1%). However, more (P<0.05) female fetuses were obtained from ExB (43.5%) and B (36.2%) compared to EB (17.4%) and M (2.9%) with EB superior to M. No differences were noted in the rates of male fetuses from embryos at the ExB (37.2%), B (28.2%), and EB (30.8%) stages, but these were higher (P<0.05)than for M (3.8%). The results indicate that the proportion of sex was skewed in favor of females among in vitro-derived expanded blastocyst and blastocyst, and in favor of males among expanded blastocyst, blastocyst and early blastocyst stages. Under the conditions described here, advanced stages of development produced similar percentages of either male or female fetuses, while early blastocyst stage leads to a higher proportion of males. Authors gratefully acknowledge FAPESP; Fortaleza and Cafezinho, Aracatuba,SP, Brazil.

KEY WORDS: fetal sexing, bovine, gender determination, ultrasound