Abstract
The increasing use of in vitro embryo production (IVP) followed by embryo transfer (ET), alongside with cryopreservation of embryos, has risen concerns regarding the possible altered pregnancy rates, calving or even neonatal mortality. One of the hypotheses for these alterations is the current culture conditions of the IVP. In an attempt to better mimic the physiological milieu, embryos were produced with female reproductive fluids (RF) as supplements to culture medium, and another group of embryos were supplemented with bovine serum albumin (BSA) as in vitro control. Embryos were cryopreserved and transferred while, in parallel, an in vivo control (artificial insemination, AI) with the same bull used for IVP was included. An overview on pregnancy rates, recipients' hormonal levels, parturition, and resulting calves were recorded. Results show much similarity between groups in terms of pregnancy rates, gestation length and calves' weight. Nonetheless, several differences on hormonal levels were noted between recipients carrying AI embryos especially when compared to BSA. Some calving issues and neonatal mortality were observed in both IVP groups. In conclusion, most of the parameters studied were similar between both types of IVP derived embryos and the in vivo-derived embryos, suggesting that the IVP technology used was efficient enough for the safe production of calves.
Highlights
In 2018, more than 1 million bovine embryos were produced worldwide from which the majority were in vitro produced (IVP) [1]
We followed two different approaches: In the first one, we evaluated the three groups (AI, bovine serum albumin (BSA) and reproductive fluids (RF)) independently; in the second one, we compared the data from artificial insemination (AI) group versus the pooled data of BSA and RF groups, with the intention of getting information about the effect of the assisted reproductive technologies (ART) procedure used (i.e., in vivo fertilized embryos (AI) versus in vitro produced embryos, where IVP = RF + BSA data)
Despite not showing any improvement of blastocyst yield, embryos produced with RF supplementation showed higher survivability after vitrification-warming than serum-derived embryos, a downregulation of genes related with oxidative stress in comparison with BSA-derived embryos as well as significantly lower reactive oxygen species when compared to both serum and BSA groups
Summary
In 2018, more than 1 million bovine embryos were produced worldwide from which the majority were in vitro produced (IVP) [1]. The use of IVP-embryos is a better option during season of heat-stress [5] or in cases of repeat breeders [6] Another technique on the rise is the cryopreservation of embryos, with more than 38% of 20180 s embryo transfers (ET) coming from frozen embryos [1]. The need for exchange of cattle genetics has popularized this embryo preservation technique, which has the added benefit to not have all the recipients synchronized at the time of fresh embryo production Within these large numbers of ET of frozen embryos, almost half (>46%) were IVP-derived embryos, but only a very small percentage of these (
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