Short-term culture of bovine bisected embryos effects on pregnancy rates, sex ratio and birth weight of calves

This study evaluated pregnancy rate, gestation length, calving rate, and also sex proportion and birth weight of calves derived from in vitro reconstructed bovine demi-embryos. Recovered embryos (grade I morulae) from superovulated cows were bisected with a steel blade and transferred to recipient heifers either immediately (group 1, n=38) or after a 24h period in culture medium (EARLE + 10% FCS) at 38.5 °C and 5% CO2 (group 2, n=34) when showed a reconstituted appearance. Intact, uncultured embryos immediately transferred to recipients after collection (group 3, n=36) were used as control. Data were analyzed by ANOVA and Chi-square test. In vitro cultured demi-embryos that developed from morulae to blastocyst (78%, 44/56) were considered viable. Pregnancy rate at day 45 was 47.4%, 52.9%, and 52.8% for groups 1, 2, and 3 respectively (P> 0.05). Calving rate reached 26.3% in group 1. 29.4% in group 2, and 30.6% in group 3 (P> 0.05). No difference was found regarding pregnancy length (280.8 ± 1.8, 285.5 ± 1.7 and 285.3 ± 1.7 days), male proportion (60%, 50% and 54.5%) and birth weight of calves (38 ± 4.2, 32.4 ± 2.5 and 36.2 ± 2.6 kg) among groups 1, 2 and 3, respectively. It was concluded that even though in vitro reconstructed demi-embryos transfer can be of some utility to select the viability of demi-embryos, this procedure is not able to improve pregnancy rates since it does not differ from uncultured demi-embryos. O presente estudo objetivou avaliar a taxa de prenhez, a duração da prenhez e a taxa de parição após a transferência de embriões bipartidos e reconstituídos in vitro, bem como algumas características (proporção de sexo e peso ao nascimento) dos bezerros produzidos. Embriões (mórulas grau 1) recuperados de vacas superovuladas foram bipartidos com uma lâmina metálica e transferidos em novilhas receptoras logo em seguida (grupo 1, n=38) ou após 24 horas de cultivo (meio EARLE + 10% SFB) a 38,5°C e atmosfera de 5% de CO2 (grupo 2, n=34). Como controle foram utilizados embriões intactos, não cultivados, transferidos logo após a coleta (grupo 3, n=36). Os dados foram analisados utilizando ANOVA e teste de χ2. Os hemi-embriões cultivados que evoluíram ao estágio de blastocisto (78%, 44/56) foram considerados viáveis. A taxa de prenhez no dia 45 após a transferência foi de 47,4%, 52,9% e 52,8% para os grupos 1, 2 e 3, respectivamente (P> 0,05). A taxa de parição foi de 26,3% no grupo 1, 29,4% no grupo 2 e 30,6% no grupo 3 (P> 0,05). Não houve diferen