87 Assessment of pregnancy success following transfer of embryos produced in vitro using frozen–thawed semen from cloned and noncloned Bos indicus bulls

Abstract

Assisted reproductive technologies (ART) continue to develop rapidly, allowing for the development of techniques to increase reproductive efficiency and contribute to the genetic improvement of cattle. Some of these techniques include in vitro production (IVP) of embryos and embryo transfer. These modern ART can help produce offspring with highly desirable characteristics. However, there is a lack of information on the percentage of pregnancies obtained following transfer (P/ET) of IVP embryos derived using semen of cloned Bos indicus bulls. The objective of this study was to compare embryo transfer results of IVP embryos created using frozen-thawed semen from 5 Brahman bulls (Bos indicus) with characteristics and genetics of high commercial value. The embryos were produced on two different dates, 45 days apart, using pooled oocytes harvested by ovum pickup from 15 Brahman cows at random stages of the oestrous cycle. Procedures for IVP were performed in a commercial laboratory (Genemex Internacional) in the state of Chiapas, Mexico. For IVF, conventional semen was used from 1 bull (B1) and his clone (B1²), the grandson of B1 (B2), and from 2 nonrelated bulls (B3 and B4). A total of 100 embryos were transferred nonsurgically by a private practitioner on a ranch in the state of Campeche, Mexico. The recipients were commercial crossbred cows synchronized using a FTET program. On Day 0, recipients received an intravaginal device containing 1.9 g of progesterone (CIDR) and 2 mg of oestradiol benzoate IM. On Day 8, the CIDR was removed and cows received 25 mg of dinoprost tromethamine, 200 IU of eCG, and 0.5 mg of oestradiol cypionate IM. Embryos were transferred on Day 17. The overall P/ET was 42% (42/100). The P/ET for IVP embryos produced with semen from bulls B1, B1², B2, B3, and B4 was 3/15 (20%), 3/8 (37%), 23/42 (55%), 8/20 (40%), and 5/15 (33%), respectively. The P/ET was numerically greater for embryos produced using semen from the cloned bull (37%; B1²) compared to embryos produced using semen from the original noncloned bull (20%; B1), although this difference was not statistically significant (P = 0.62, Fisher’s exact test). There was a significant difference (P < 0.05) for the P/ET obtained with embryos produced using semen from bulls B1 and B2, but results for the other bulls were not significantly different. As far as we know, this is the first scientific report in Mexico concerning the use and comparison of semen from cloned and noncloned bulls for the production and transfer of bovine IVP embryos. In general, a wide numerical range of P/ET using the different bulls was observed (i.e. 20-55%). In this preliminary study, there was no impact of using frozen-thawed semen from a cloned bull for IVP on P/ET. The results from this research can contribute to the study and development of ART to improve P/ET obtained using Zebu IVP embryos. However, further research with a larger numbers of animals is required to confirm whether using semen from cloned and noncloned Bos indicus bulls for IVP impacts pregnancy success following embryo transfer.