176 PRODUCTION OF TRANSFERABLE EMBRYOS IN BRAHMAN COWS TREATED WITH BOVINE SOMATOTROPIN

It is the goal of numerous research laboratories around the world to increase the number of transferable bovine embryos and to improve the viability of these embryos after ET into recipients. Treatment of donor cows with bovine somatotropin (bST) has given satisfactory results that have increased the hopes for an improved commercial production of embryos (Moreira et al. 2002 Theriogenology 57, 1371–1387). In order to demonstrate the effect of bST on the production of transferable embryos, degenerated embryos and non-fertilized oocites, 16 high-value genetic Brahman cows were synchronized and later subjected to a superovulatory (SO) treatment. The SO treatment consisted of decreasing doses of FSH (Folltropin-V®, Vetrepharm Inc, Ontario, Canada) every 12 h for 4 days (2.5, 2.0, 1.5, 0.5 × 2/day). Forty-eight hours after the beginning of the SO treatment, a dose of PGF2α (Lutalyse®, Upjohn, Kalamazoo, MI, USA.) was given to all donors (i.m.). Estrus was detected by careful observation. At the time of first AI (6 hours after estrus detection) all cows were given (i.m. a GnRH (Buserelin, Conceptal®, Intervet, Boxmeer, The Netherlands) analogue and randomly assigned to one of the following groups: bST (n = 8), which were treated with 500 mg (s.c.) of bST (Boostin-S®, Schering-Plough Caracas, Venezuela) or control group (n = 8) not treated. The second AI was done 10 hours after the first AI. Immediately after the uterine recovery, oocytes and embryos were evaluated and classified, according to their morphologic characteristics, into transferable embryos (TE) of good (TE1) or medium (TE2) quality, degenerated embryos (DE) and non-fertilized oocytes (NF). CL were evaluated by rectal palpation to estimate the ovulatory response. The statistical comparison between experimental groups (percentage of each category) was carried out using a chi-square test of SAS. Results are presented in Table 1. Results show that bST donor treatment increases the number and quality of transferable embryos. Key words: bST, ET, donor, embryo, superovulation. Table 1 Number and percentages of transferrable and degenerated embryos and non-fertilized oocytes in superovulated Brahman cows after treatment with bST