9 Superovulation and fixed-time embryo transfer in Romosinuano cows using a short protocol with Stimufol and equine chorionic gonadotropin

The Romosinuano is a Bos taurus breed genetically adapted to tropical conditions, but little has been done to preserve this genetic material as embryos. It is known that two of the sources of variation in embryo transfer (ET) programs are the breed and the type and dose of FSH to induce superovulation. This study was carried out to evaluate the response of Romosinuano cows to a short protocol of superovulation and fixed-time embryo transfer using a combination of FSH (Stimufol^TM) and equine chorionic gonadotropin (eCG; GonActive^TM). Five Romosinuano donors with an average age of 4.5 to 5 years, 45 days postcalving, with body condition score of 2.5 to 3 (scale 1–5) were used in this study, in the Mexican State of Veracruz. This study was carried out during the months of April and May, a period of drought in the tropical region of the Gulf of Mexico, with temperatures as high as 40°C. Prior to the start of the study, cows were evaluated by ultrasound to determine the presence of a corpus luteum or follicles larger than 10 mm in order to rule out pregnancy and anestrus. One treatment was assigned to the donors, consisting in total FSH doses of 300 mg administered in a 2-day, twice-a-day protocol, as follows: Day 0: intramuscular injection of 3 mg of oestradiol benzoate (EstroActive^TM) and insertion of a controlled internal drug release device (CIDR^TM) with 1.9 g of progesterone. Day 4: a.m. FSH, p.m. FSH. Day 5: a.m. FSH, p.m. FSH. Day 6: a.m. two doses at once of a synthetic prostaglandin F_2α (InducelActive^TM) and eCG (400 IU). Day 7: CIDR is withdrawn. Day 8: a.m. buserelin acetate 0.01 mg (LiberActive^TM); p.m.: FTAI, first AI 24 h after CIDR withdrawal or 12 h after buserelin. Day 9: a.m. FTAI, second AI 12 h later. Day 15: embryo collection and evaluation. For AI, frozen conventional semen in 0.5-mL straws (30 million sperm per straw) from two Romosinuano bulls was used. Semen was evaluated with a field microscope, showing a minimum post-thaw motility of 40%. The AI and embryo collection procedures were carried out by a single technician. The results of the first program, performed in April, had an embryo production rate of 30 viable embryos with six embryos/donor on average compared to the procedure in May, with results of 18 viable embryos with 3.6 embryos/donor on average, respectively. The two protocols performed produced a total of 48 viable embryos collected in two attempts, using the same five donors, with an average of 4.8 viable embryos/donor. In conclusion, the cows showed good response to superovulation in terms of total viable embryos retrieved, with the program performed in April producing higher percentages than in May. There were differences in the two programs evaluated, and overall, the transferable embryo production was acceptable compared with results obtained in other breeds, but similar when compared to responses obtained with tropically adapted Bos taurus breeds. Based on these results, the protocol evaluated can be used with donors of the same age range, expecting similar results, with the advantage of the lower cost and easier management of this short protocol. The results also seem to indicate that season is another cause of variation in superovulatory treatments and embryo production, even in breeds genetically adapted to tropical environments. Further study is required using statistical analysis for evaluating differences in environmental factors.