Climate change has caused heat stress (HS) to become an increasingly severe problem for high-producing dairy herds. Although cooling systems allow milk production to remain nearly constant throughout the year, fertility decreases during summer. Physiological counter-current heat transfer mechanisms maintaining brain/hypothalamic and reproductive functions in cattle are vulnerable to HS. In this study, I propose strategies to improve cooling systems, particularly in zones with the highest risk of increased body temperature, such as milking areas. In addition, heat transfer mechanisms to protect the brain–hypothalamus axis from hyperthermia must be considered when implementing measures to reduce HS-related problems.

Hypothalamic arcuate (ARC) kisspeptin neurons are considered the gonadotropin-releasing hormone pulse generator in rats. In virgin rats, the expression of the ARC kisspeptin gene (Kiss1) is repressed by proestrous levels of estradiol-17β (high E2) but not by diestrous levels of E2 (low E2). In lactating rats, ARC Kiss1 expression is repressed by low E2 during late lactation. This study aimed to investigate whether nuclear receptor corepressor 2 (NCOR2, encoded by Ncor2), an estrogen receptor α corepressor, is involved in the estrogen-induced repression of ARC Kiss1 expression in rats. Double in situ hybridization for Kiss1 and Ncor2 revealed that approximately 80% of ARC Kiss1-expressing cells co-expressed Ncor2 in ovariectomized (OVX) + low E2 virgin rats, while approximately 90% of ARC Kiss1-expressing cells co-expressed Ncor2 in OVX + low E2 lactating rats. To further examine the role of Ncor2, we studied the effects of Kiss1-dependent Ncor2 knockdown on ARC Kiss1 expression and luteinizing hormone (LH) pulses. An adeno-associated virus vector carrying Cre-activated short hairpin RNA (shRNA) for Ncor2 was administered to the ARC in two Kiss1-Cre rat models: OVX + high E2 Kiss1-Cre virgin rats and OVX + low E2 Kiss1-Cre lactating rats. Ncor2-shRNA treatment significantly increased the number of ARC Kiss1-expressing cells and the intensity of Kiss1 signals in OVX + high E2 virgin rats but failed to fully restore low E2-induced Kiss1 repression in lactating rats. The Ncor2-shRNA treatment failed to affect LH pulses in both models. These findings suggest that NCOR2 in ARC kisspeptin neurons mediates high E2-induced repression of ARC Kiss1 expression in virgin rats.

The neurotransmitter, 5-hydroxytriptamine (5-HT), is well known. Furthermore, it enhances the acrosome reaction, hyperactivation, and in vitro fertilization (IVF) success in hamsters and mice. In the present study, we examined whether 5-HT enhances hyperactivation and increases IVF success in rats. When rat sperm was exposed to 5-HT, hyperactivation was significantly enhanced. Only the 5-HT₄ receptor agonists significantly enhanced hyperactivation. Additionally, both 5-HT and 5-HT₄ receptor agonists significantly increase the success of IVF. These results suggested that 5-HT increases IVF success by enhancing hyperactivation and effects of 5-HT are associated with the 5-HT₄ receptor. Therefore, in rats, 5-HT enhances capacitation and the 5-HT₄ receptor is the key molecule for capacitation.

In Japanese Black (JB) cattle, the number of transferable embryos produced after superovulation is crucial for the economic success of embryo production for both farmers and veterinarians. Anti-Müllerian hormone (AMH) has emerged as a key reproductive marker for predicting the number of embryos produced in vivo and oocytes retrieved through transvaginal pickup. This study investigated the relationship between AMH, inflammatory markers, including serum amyloid A (SAA) and albumin/globulin (A/G) ratio, and the number of embryos recovered and transferable after superovulation in JB cows. A total of 96 JB donor cows underwent artificial insemination after superovulation, and embryo recovery was performed 7 days later. Embryos recovered were classified based on the International Embryo Technology Society criteria, wherein “transferable embryos” included those with codes 1 or 2, while “total embryos” included transferable embryos as well as those with codes 3 and 4. Blood samples collected during embryo recovery were used to measure serum AMH, SAA, and A/G ratios. When grouped by AMH quartiles, the high-AMH and middle-high-AMH groups produced significantly more total embryos compared to the low-AMH group. The total number of embryos increased with higher AMH levels (r = 0.3336, P = 0.0009). Correlation analysis revealed associations between AMH, α₁-globulin and SAA. Additionally, a significant positive correlation was observed between total and transferable embryos (r = 0.6339, P < 0.0001) and between AMH and the yield ratio (r = 0.25583, P = 0.0119). These findings confirm that AMH concentration is a valuable reproductive marker for predicting the total and transferable embryos produced by JB donor cows.

In vitro production of porcine-hatched blastocysts is important for various applications. However, the mechanobiology of blastocoel expansion and hatching remains poorly understood. Our study aimed to efficiently produce hatched blastocysts and investigate the hatching mechanics of late-stage porcine embryos using time-lapse assessment. In this study, fetal bovine serum (FBS), amino acids (AA), and insulin-transferrin-selenium (ITS) were added individually or in combination to culture day 5 parthenogenetic morulae and early blastocysts to investigate their developmental capacity. We found that FBS-AA-ITS supplementation significantly promoted blastocoel expansion (4.4-fold), accelerated early hatching (at day 6 vs. day 7.5) and improved hatching rates (39.59 ± 4.34% vs. 0 ± 0% on day 7, and 80.02 ± 2.93% vs. 2.78 ± 1.60% on day 8) compared with non-supplemented controls. It also increased the number of trophectoderm (2.5-fold) and inner cell mass (2.7-fold). Furthermore, FBS-AA-ITS elevated BCL2 expression and reduced BAX expression, potentially inhibiting apoptosis. In in vitro fertilized embryos, the combination also significantly improved the hatching rate (8.3-fold) and cell number (2.7-fold). Analysis of the effects of FBS on hatching dynamics revealed that FBS enhanced hatching by increasing the number of blastomeres and blastocoel diameter. Blastocysts supplemented with FBS had significantly smaller hatching sizes (320.09 ± 5.01 µm vs. 343.95 ± 5.67 µm) and faster rate of hatching progress (5.6-fold) compared with non-FBS groups. In conclusion, FBS-AA-ITS played a pivotal role in supporting the development of late-stage porcine embryos and significantly accelerated their progression through the embryonic developmental phase.

The efficiency of porcine in vitro fertilized (IVF) embryo production remains low. Polyspermy is considered a contributing factor to this result. In this study, we investigated the effects of mechanical vibrations during the co-culture of oocytes and spermatozoa on fertilization parameters and subsequent embryonic development. The rate of polyspermy decreased significantly in all vibration culture groups compared with the stationary culture (control) group (P < 0.05). Regarding subsequent embryonic development, the blastocyst formation rate was significantly improved in the middle-vibration culture group compared with the control group (P < 0.05). However, the high-vibration culture group had the lowest sperm penetration rate and did not show any improvement in monospermy rate and normal fertilization efficiency. In addition, their in vitro developmental status was the lowest. These results indicate that moderate mechanical vibrations during insemination effectively suppress polyspermy and improve porcine IVF embryo production efficiency.