Abstract
The objective was to determine the effect of some factors on pregnancy rate of fixed-time embryo transfer (FTET), in cows and heifers kept under Mexican tropical conditions. Recipients females (n=405) grazing in pastures were selected according to breed group (Zebu and crosses), parity (nulliparous and multiparous), body condition score (BCS) and the presence of a corpus luteum (CL). The females were synchronized on day 0 using a progesterone vaginal device and 2 mg estradiol benzoate (EB), two groups were established. Group 1 (conventional protocol) were animals in which the progesterone device was removed on day 7. At this time, also received an injection of 50 mg cloprostenol sodium and 1 mg estradiol cypionate. Animals also received 300 IU (heifers) or 360 IU (cows) of eCG. Group 2 (J-Synch protocol) were animals in which the progesterone device was removed on day 6. Cloprotenol and eCG injections were applied as in Group 1. Additionally, on day 9, animals of group 2 received 0.01 mg buserelin acetate. Embryo transfer of in vivo or in vitro was done on day 16 and pregnancy diagnosis was realized by ultrasonography on days 23 and 53 after FTET. Statistical analyses were carried out using Chi-square tests and logistic regression. Pregnancy rate varied between farms (P<0.05). The highest pregnancy rate was for multiparous cows (66%). The recipient utilization rate was better in the J-Synch protocol (85%), and in vivo embryos (75%) had higher pregnancy rate. The diameter of the follicle and the CL had no effect on pregnancy rate (P>0.05). However, the logistic regression determined that the only significant factor on pregnancy rate was the type of embryo. In conclusion, pregnancy rate in FTET females was higher for in vivo embryos than for in vitro embryos in cows evaluated under humid tropical conditions in Mexico.
Highlights
In Mexico, as in other parts of the world, the implementation of reproductive biotechnologies such as multiple ovulation and embryo transfer (MOET), and in vitro fertilization (IVF) are important tools for disseminating animals with high genetic merit, to improve productive performance of cattle herds
The diameter of the follicle and the corpus luteum (CL) had no effect on pregnancy rate (P>0.05)
Pregnancy rate in fixed-time embryo transfer (FTET) females was higher for in vivo embryos than for in vitro embryos in cows evaluated under humid tropical conditions in Mexico
Summary
In Mexico, as in other parts of the world, the implementation of reproductive biotechnologies such as multiple ovulation and embryo transfer (MOET), and in vitro fertilization (IVF) are important tools for disseminating animals with high genetic merit, to improve productive performance of cattle herds. The success of embryo transfer depends on factors associated with recipient selection, synchronization protocol used and embryo production method. Some factors to consider when selecting female recipients are type of cattle, Bos indicus, Bos taurus or the crosses of both (McEvoy et al, 2006), parity (nulliparous or multiparous), body condition score (BCS), management, reproductive and nutritional status (Bó et al, 2012; Wu and Zan, 2012).
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