Cover Story: To improve the reproductivity of dairy cows, which has been continuously decreasing, it is important to note that the detection of estrus should be accurate and that the timing of AI should be appropriately decided. However, the relationship between the conception rate and the timing of AI after the onset of estrus or ovulation period, following the performance of AI using the frozen-thawed semen, has not been investigated yet. However, Sumiyoshi et al. investigated the relationship between the ovulation time after AI and the conception rate, and identified the time span during which the frozen-thawed semen delivers high conception rate after its deposition in the uterus (Sumiyoshi et al., An investigation of the time period within which frozen-thawed semen delivers a high conception rate in lactating dairy cows, pp.277-280). In this study, the authors demonstrated that high conception rates averaging 63.0% were obtained by performing AI 6-30h before ovulation, which was significantly higher than the conception rates of 30.0% (P<0.05) and 26.9% (P<0.01) obtained from AI that was performed earlier than 30h before ovulation and later than 6h before ovulation, respectively. These results further suggest that the frozen-thawed semen can deliver a conception rate of ≥60% if it deposits in the uterus for more than 24-30h after AI, and also that a conception rate of ≥60% can be achieved by performing AI 6-30h before ovulation by using the frozen-thawed semen.
Most primordial follicles present in ovaries are dormant and only a few of them are activated in every estrus cycle. However, the mechanism controlling the activation of dormant primordial follicles in vivo remains unclear. In this study, Komatsu et al. found that almost all the activated primordial follicles (black arrows) made contact with blood vessels (red arrows) in mouse ovaries (Komatsu et al. Increased supply from blood vessels promotes the activation of dormant primordial follicles in mouse ovaries. pp. 105–113). To confirm the hypothesis that angiogenesis is crucial for activation of the dormant primordial follicles in vivo, Komatsu et al. induced angiogenesis using recombinant VEGF. They found that the activation of dormant primordial follicles was promoted by an increase in the number of blood vessels in the ovaries. Furthermore, the number of activated follicles increased in cultured ovarian tissues depending on the serum concentration in the medium. These results confirm that the supply of serum components through new blood vessels formed via angiogenesis is a cue for the activation of dormant primordial follicles in the ovaries.
Improving artificial oocyte activation is essential for animal biotechnology, to obtain healthy offspring with a high success rate. Yamamoto et al. investigated whether the equine sperm-specific phospholipase C zeta (ePLCζ) mRNA, which has the strongest oocyte activation potential in mammals, could improve the mouse oocyte activation rate and subsequent embryonic development using inactivated spermatozoa (Yamamoto et al. Production of mouse offspring from inactivated spermatozoa using horse PLCζ mRNA. pp. 67–73). The activation potential of ePLCζ was ten times greater than that of murine (m) PLCζ and normal blastocysts were obtained. However, the birth rate was slightly, but significantly, decreased in oocytes activated by ePLCζ compared to those activated by mPLCζ. These results suggest that activation rate does not always correlate birth rate.
Neuroendocrine Mechanisms Regulating Pulsatile Luteinizing Hormone Secretion
Released: October 20, 2010 | Volume 41 Issue 6 Pages j103-j111
Effects of Food Restriction on Spermatogenesis in Rats
Released: October 20, 2010 | Volume 42 Issue 6 Pages j69-j75
Makoto SHIMADA, Yukari SHIKANAI, Shigeo HARADA
Neuroendocrine Mechanism Regulating Luteinizing Hormone Secretion during Periovulatory Period: Negative and Positive Feedback Actions of Estrogen in the Brain
Released: October 20, 2010 | Volume 44 Issue 6 Pages j81-j90
Corpus Luteum Function and Its Morphological Characteristics in Cattle
Released: October 20, 2010 | Volume 43 Issue 6 Pages j55-j64
Adaptations for Brood Parasitism in Cuculus Cuckoos
Released: October 20, 2010 | Volume 41 Issue 6 Pages j127-j133