The aim of this study was to assessed the differences in embryos quality between the natural estrus and two systems of estrus synchronization in multiparous sows and prepuberal gilts. In this experiment, multiparous sows (n = 63) and prepuberal gilts (n = 42) were used. The subgroups of these animals were treated with PMSG (1500 U.I.) + hCG (500 U.I.) or PG-600 synchronization systems. These animals were inseminated twice, 24 and 36 h after hCG injection. The control gilts (n = 20) were from the third subgroup and were inseminated two times at 12 h intervals during their natural estrus cycles. A statistically significant increased number of corpora lutea (CL) and embryos was observed between natural estrus and both synchronization systems in multiparous sows (p < 0.001). There were no differences found in the number of degenerative embryos isolated from both ovaries between PMSG + hCG, PG-600, and natural estrus groups in multiparous sows (p = 0.484), (p = 0.279), (p = 0.213), (p = 0.138), respectively. However, an increased number of unfertilized oocytes in multiparous sows after treatment with PMSG + hCG as compared to control animals (p = 0.041) was observed. A statistically higher number of embryos after treatment with PMSG + hCG was also observed in the separate groups of multiparous sows and prepuberal gilts as compared to PG-600 treated animals. No differences were found, however, in the number of degenerative embryos between those two separate groups of animals after treatment with PMSG + hCG and PG-600 of both ovaries: (p = 0.175), (p = 0.344), (p = 0.122), and (p = 0.055), respectively. It can be suggested that the differences in the number of embryos isolated from both ovaries after these two treatments systems in prepuberal gilts and multiparous sows may be a result of age-dependent different response to gonadotropins and the reproductive competence of these females.
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