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Despite extensive research on the reproductive health of domestic animals, embryonic mortality continues to be a problem that brings about significant losses for both commercial breeding and scientific research. This review paper discusses the genetic and environmental factors that affect embryo mortality rates in sheep along with the different techniques developed to overcome this issue. Additionally, one of the objectives of this study is to emphasize the importance of the use of time-lapse cinematography and color Doppler ultrasonography as quick and reliable methods for early detection of pregnancy and embryonic death.

Background Ultrasonography is one of the most important techniques that enable the detection and monitoring of pregnancy. One such study using this technique is the assessment of the hemodynamics of fetal and umbilical blood vessels. However, there is little data on blood flow in the placentomes, which is the basic structural unit of the sheep’s placenta. Therefore, the aim of this study was to determine the Doppler parameters in the arterial vessels of the caruncles, cotyledons and the umbilical cord as well as measuring venous flow rates during the entire gestation period of the sheep. Additionally, the usefulness of various other ultrasound parameters in the early diagnosis of pregnancy in sheep was analyzed. Results Most of the Doppler parameters in umbilical, cotyledonary and caruncular arteries were significantly correlated with the day of pregnancy (p < 0.01). In the early stages of pregnancy, the peak systolic velocity (PSV), regardless of the location of the artery, was significantly lower than that in the later stages of pregnancy (p < 0.01). PSV was also found to be significantly higher in the umbilical artery than in the cotyledonary and caruncular arteries (p < 0.01). Until the 50th day of pregnancy, the end diastolic velocity (EDV) was not found in the umbilical and cotyledonary arteries. EDV was significantly higher in the caruncular arteries than in the cotyledonary and umbilical arteries (p < 0.01). The resistance index (RI) and pulsatility index (PI) in the early stages of pregnancy were found to be significantly higher than that in the later stages of pregnancy (p < 0.01). The RI and PI were significantly lower in the caruncular arteries than in the arteries of the cotyledons and umbilical cord (p < 0.01). In the umbilical vein, all Doppler parameters were observed to be significantly higher than those in the placentomal veins (p < 0.01 or p < 0.05). Using transrectal ultrasound, pregnancy was detected between 20 and 28 days after mating. The ovaries were observed to have corpora lutea, the diameter of which was fairly consistent from the 17th to the 56th day of pregnancy. Conclusions It has been demonstrated that both the location of the arterial vessel in the placental-umbilical circulation and the gestational age have a significant impact on hemodynamic parameters. The results also provide new insights about the blood flow in caruncular and cotyledonary arteries, which could contribute to a more holistic understanding of hemodynamic changes in the placentas of sheep. Analyzing haemodynamic parameters in the umbilical and placental veins are preliminary studies in sheep, but it could inspire further research in this field. Furthermore, the research conducted confirms the practicality and convenience of transrectal ultrasonography in the early diagnosis of pregnancy in sheep and also indicates that the identification and imaging of the corpus luteum using B-mode ultrasonography can be a very early and simple method of confirming effective mating in sheep.

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Polyspermic fertilisation has been a continual problem in porcine in vitro fertilisation. Over the years, researchers have tried to resolve this persistent problem, but have not been entirely successful in their endeavour. This can be attributed to several factors. This review discusses the role of sperm capacitation in the in vitro fertilisation and the most recent studies on the capacitation media. This includes the results obtained by testing the effect of various compounds on sperm capacitation. Additionally, the importance of the oviductal fluid on the porcine oocytes prior to fertilisation is also discussed. This is of significance, as the experiments show that oviductal fluid is crucial for the pre-fertilisation zona pellucida hardening. Also, the significance of using high quality oocytes for the in vitro fertilisation is highlighted. Lastly, the different and latest techniques to prevent or reduce polyspermic fertilisation have been reviewed.