182 MANAGING FACTORS ASSOCIATED WITH PREGNANCY RATE OF HEIFER RECIPIENTS IN LARGE IN VITRO PRODUCED EMBRYO PROGRAMS

Abstract

Large programs of in vitro embryo production have been developed in Brazil, but the results are very variable. The objective of this study was to evaluate managing factors that influence pregnancy rate of recipients in a large embryo transfer program. Results of 1104 embryo transfers performed from November 2008 to February 2009 by Transgen Desenvolvimento e Produção Agropecuária Ltda (Uberlˆndia, Minas Gerais, Brazil) were evaluated. Embryos produced in vitro were used: 1/2 Holstein/Gir embryos (n = 139) or 3/4 Holstein/Gir embryos (n = 961) produced from donors 1/2 Holstein/Gir and Gir with Holstein bull semen. Only excellent (grade 1) quality morulae (stage 4), early blastocysts (stage 5), mid- blastocysts (stage 6), or expanded blastocysts (stage 7) were assigned for fresh transfer using the International Embryo Transfer Society guideline for grading embryos. The heifer recipients were 1/2 crossbred Nelore/Simmental, in good health condition, 20 to 30 months of age, 330 to 400 kg of weight, and were maintained on pasture (Tifton) with mineral supplementation ad libitum. The recipients were synchronized as follows: Day 0-intravaginal device with 1.0 g of progesterone (PRIMER^®, Tecnopec, São Paulo, SP, Brazil) +2 mg of estradiol benzoate (ESTROGIN^®, Farmavet, São Paulo, SP, Brazil); Day 5-150 μg of D-Cloprostenol (PRELOBAN^® Intervet, São Paulo, SP, Brazil) + 400IU of eCG (FOLLIGON^®, Intervet); Day 8-progesterone device removed; Day 9-1 mg of estradiol benzoate. On Day 17, nonsurgical embryo transfers were performed by a trained technician and synchronization was confirmed by presence of a CL. The effects of the embryo breed, the number of transfers in each recipient (the heifers that failed to get pregnant were used in the next program), and the transfer sequence (i.e. 20 embryo transfers were performed per hour, and approximately 100 per day) on the pregnancy rate was analyzed by logistic regression with the LOGISTIC procedure of SAS (SAS Institute Inc., Cary, NC, USA). The breed of embryo (56.9% for 3/4 Holstein/Gir embryos v. 62.6% for 1/2 Holstein/Gir embryos), the number of transfers in each recipient (first: 56.5% v. second: 61.8% v. third: 55.5% v. ≥fourth: 55.0%), and the transfer sequence during the day of the program (first hour: 57.4% v. second hour: 60.0% v. third hour: 58.1% v. ≥fourth hour: 53.8%) did not influence the pregnancy rate. Within the confines of an extensive embryo transfer program with in vitro produced fresh embryos, a large number of embryo transfers can be executed per day without adversely affecting the pregnancy rate if high-quality embryos are used, the transfers are performed by a trained technician, and recipients are in good health condition and synchronized.