293 FACTORS ASSOCIATED WITH PREGNANCY OUTCOMES OF IN VITRO-PRODUCED EMBRYOS IN ZEBU CATTLE

Abstract

Few studies have addressed the factors that can affect pregnancy rates of in vitro-produced embryos (IVPE) and fewer still when referring to zebu IVPE. This study aimed to estimate some of these factors and the proportion of pregnancy loss. A total of 1227 pure-breed IVPE (Brahman, Red Brahman, and Gyr) were transferred (ET) to an equal number of crossbred Bos indicus × Bos taurus heifers. Recipients averaged 420 kg, were grass fed, and kept in three different ET Centrals located in northern, central, and eastern regions of Colombia. IVPE (Embriogen, Bogotá, Colombia) were nonsurgically transferred into synchronized recipients by using the following protocol: Day 0 s.c. implant of norgestomet 3 mg, plus an i.m. injection of estradiol valerate 5 mg and norgestomet 3 mg; Day 7 D-cloprostenol 0.15 mg i.m. Day 9 implant removal plus 200IU of eCGi.m. Pregnancy was recorded on Days 30 and 60 by ultrasound with an 8-m Hz linear rectal probe. Data were collected for 1 year beginning in September 2007. Binary logistic regression with forward conditional elimination was performed to evaluate factors associated with pregnancy. The strength of the association between the studied variables and pregnancy rate was estimated by the odds ratio (OR) (95% CI); a P-value < 0.05 indicated statistical significance. Interaction terms were considered (SPSS Inc., Chicago, IL, USA). Variables included in the logistic model were CL diameter at the time of ET, number of previous transfers to a recipient before achieving pregnancy, difficulty during the ET, embryo quality and stage, technician and level of training, number of transferred embryos by technician per day, uterine horn where the embryo was delivered, time between laboratory release and ET, ET Central, period of the year when the ET was performed, sire and breed of the embryo. Total pregnancy rate was 38% on Day 60 (462/1227), and the proportion of pregnancy loss was 8% between Days 30 and 90. Factors associated with pregnancy were as follows: 1) excellent embryos were 2.3 times more likely to achieve pregnancy (39%) than good embryos (21%), OR = 2.3, 95%CI = 1.4-3.8, P = 0.001; 2) easy transferred embryos were 5.1 times more likely to result in pregnancy (49%) compared with difficult transferred embryos (11%), OR = 5.1, 95% CI = 2.5-10.3, P < 0.05; and 3) transferred embryos <5 h after being released from the laboratory resulted in higher pregnancy rate (42%) than those transferred >5 h (33%). No interactions were found in the final logistic model. In conclusion, pregnancy outcome of IVPE Bos indicus was strongly associated with quality of the embryo, level of difficulty at the moment of the ET, and the time between the production of the embryo and the ET. In addition, the observed low pregnancy loss in this study suggests careful selection and management of the recipients, adequate handling of the IVPE, and proper training of the ET technicians.

Embriogen S.A. Bogotá, Colombia. Cenatte, Pedroleopoldo, MG, Brazil.