No abstract

Synchronization of estrus and ovulation are of paramount importance in modern livestock improvement programs. These methods are critical for assisted reproduction technologies, including artificial insemination and embryo transfer, that can increase productivity. In the current study, subcutaneous implants containing norgestomet were placed for long (14 days), medium (9 days), and short (5 days) periods of time in 70 crossbred ewes undergoing fixed-time artificial insemination. The resulting effects on estrus synchronization and conception rates were subsequently evaluated. Among the synchronized ewes, 85.7% (60/70) underwent estrus over a period of 72 h after progestagen treatment ceased. The shortest mean interval between withdrawal of the device and onset of estrus (34.2 ± 8.9 h) was observed in the G14 days of P4 group (p < 0.05). The conception rate of the G14 days of P4 group was statistically higher than that of the other groups (83.3% vs. 60.9% vs. 47.8%; p < 0.05). In conclusion, 14 days of norgestomet treatment produced higher conception rates and a greater number of pregnancies at the beginning of the breeding season.

No abstract

No abstract

The aims of this study were to determine if the protein source of the medium influences zebu embryo development and if developmental kinetics, developmental block and programmed cell death are related. The culture medium was supplemented with either fetal calf serum or bovine serum albumin. The embryos were classified as Fast (n = 1,235) or Slow (n = 485) based on the time required to reach the fourth cell cycle (48 h and 90 h post insemination - hpi -, respectively). The Slow group was further separated into two groups: those presenting exactly 4 cells at 48 hpi (Slow/4 cells) and those that reached the fourth cell cycle at 90 hpi (Slow). Blastocyst quality, DNA fragmentation, mitochondrial membrane potential and signs of apoptosis or necrosis were evaluated. The Slow group had higher incidence of developmental block than the Fast group. The embryos supplemented with fetal calf serum had lower quality. DNA fragmentation and mitochondrial membrane potential were absent in embryos at 48 hpi but present at 90 hpi. Early signs of apoptosis were more frequent in the Slow and Slow/4 cell groups than in the Fast group. We concluded that fetal calf serum reduces blastocyst development and quality, but the mechanism appears to be independent of DNA fragmentation. The apoptotic cells detected at 48 hpi reveal a possible mechanism of programmed cell death activation prior to genome activation. The apoptotic cells observed in the slow-developing embryos suggested a relationship between programmed cell death and embryonic developmental kinetics in zebu in vitro-produced embryos.

The aims of this study were to investigate whether the number of antral follicles (AF) in the ovaries of Nelore cows is influenced with the developmental competence of oocytes to reach the blastocyst stage and to quantify the mRNA abundance of genes associated with folliculogenesis and oogenesis in granulosa and cumulus cells. A total of 168 cows were distributed into two experimental groups according to the number of AF, low (≤31) and high AF (≥92), which were determined based on the mean number of AF (61.14) ± SD (30.43). Granulosa and cumulus cells were used to assess the mRNA expression of 16 genes. Cumulus cells from cows with low AF had higher mRNA expression of genes involved in meiosis resumption (NPR-2, NPR-3) and cumulus cell expansion (FGF10), as well as a transcription factor involved in the regulation of oocyte maturation and cell proliferation (STAT3). Conversely, granulosa cells from females with high AF had higher expression of PGR and AMHR2a, which are involved in meiosis resumption and cumulus cell expansion. Cumulus-oocyte complexes (COCs) were collected from 356 cows with low and high AF populations to evaluate embryo development. Cleavage and blastocyst rates did not differ between the groups. In conclusion, our findings revealed that genes involved in folliculogenesis and oogenesis are differently expressed in cumulus and granulosa cells of cows having low and high numbers of AF. These molecular differences suggest that the regulation of oocyte maturation, meiotic resumption and cumulus expansion may be influenced by the number of AFs. However, the variations in gene expression were not associated with in vitro oocyte developmental competence to reach the blastocyst stage, which confirms that oocytes from Nelore cows with low and high numbers of AF are similarly able to mature, regulate the fertilization process and support pre-implantation embryo development.

No abstract

The aims of this study were I) to compare the follicular diameter, corpus luteum diameter and serum progesterone (P4) concentrations in cows treated with conventional protocol vs. injectable P4 protocol; II) to determine the serum P4 profile in ovariectomized heifers; and III) to compare pregnancy rate between protocols. In experiment I, multiparous cows received a protocol for ovulation synchronization with an intravaginal P4 device (n = 38; device + EB day 0; device removal + PGF2α + eCG + EC day 8) or injectable P4 (n = 38; injection + EB day 0; PGF2α + eCG + EC day 8). In experiment II, ovariectomized heifers (n = 8) were treated with injectable P4 and blood samples were collected to determine the serum P4 profile. In experiment III, multiparous cows were timed AI with two different P4 approaches, intravaginal P4 device (n = 48) or injectable P4 (n = 47). In the first experiment, cows treated with P4 device had higher (P < 0.05) diameter of dominant follicle after ovulation induction (11.6 ± 1.8 vs.10.3 ± 1.8 mm) and ovulation rate (97%, 37/38 vs. 47.3%, 18/38) than cows treated with injectable P4. But, the follicular growth daily was higher (P < 0.05) in cows treated with injectable P4 than intravaginal device (1.3 ± 0.4 vs. 1.0 ± 0.3 mm/day, respectively). In experiment II, the P4 concentration peak occurred within 48 hours (6.54 ng/mL) and decreased after 96 hours (P < 0.05) after P4 injection. In experiment III, cows with P4 device had higher (P < 0.05) pregnancy rate than the injectable P4 group (60.4 vs. 34.0%, respectively). These results demonstrate that although the intravaginal P4 devices showed a higher pregnancy rate, a protocol with injectable P4 represents an easier method and a promising alternative for TAI in cattle.