Animal Molecular Breeding 2024, Vol.14, No.3, 217-227 http://animalscipublisher.com/index.php/amb 220 Non-surgical methods are preferred due to their lower risk and higher acceptance among breeders. The use of ultrasonography to guide the transfer process can improve the accuracy and success rates of ET. It is essential to ensure that the recipient queen has a functional corpus luteum (CL) at the time of transfer, as this is critical for maintaining pregnancy (Bonacker et al., 2020). The quality and stage of the embryos also play a significant role in the success of the transfer, with blastocyst stage embryos often showing better outcomes compared to earlier stages (Baruselli et al., 2010). 4.4 Post-transfer care and monitoring Post-transfer care and monitoring are essential to ensure the success of the ET program. Recipient queens should be monitored for signs of estrus and pregnancy, with regular ultrasonographic examinations to confirm the presence and development of embryos. Proper nutrition and stress management are crucial during this period to support the queen’s health and the development of the embryos. Additionally, monitoring progesterone levels can help in assessing the queen’s readiness to support pregnancy and in making necessary adjustments to the care regimen (Phillips et al., 2016; Wiltbank et al., 2019). By following these optimized protocols, feline breeding programs can improve the efficiency and success rates of embryo transfer, ultimately contributing to better genetic management and breeding outcomes. 5 Factors Influencing Embryo Transfer Success 5.1 Genetic and health status of donor and recipient The genetic and health status of both the donor and recipient cats play a crucial role in the success of embryo transfer. Studies have shown that the reproductive status and health of the donor significantly affect the quality and viability of the embryos produced (Figure 1). For instance, non-lactating donor cows produced a larger number of viable embryos compared to lactating cows, indicating that the physiological state of the donor can impact embryo quality (Lamas et al., 2020). Additionally, recipient health, including uterine pathology and endometrial thickness, has been identified as a critical determinant of successful embryo implantation and pregnancy outcomes. The two charts from Currin et al. (2022) clearly demonstrate the impact of the donor bull and semen concentration on embryo development in in vitro fertilization (IVF). Chart A illustrates how the genetic background of different bulls significantly affects embryo cleavage, the embryo/oocyte ratio, and the embryo/cleaved embryo ratio. This reflects the importance of the donor's genetic health in the success rate of IVF. Chart B further explores the effect of semen concentration on a specific donor bull (Bull D), showing variability in how semen concentration influences embryo development, which may be related to the donor's reproductive health and genetic quality. These findings emphasize the importance of selecting donors with healthy and superior genetic traits to optimize IVF outcomes. 5.2 Quality of embryos The quality of the embryos being transferred is another pivotal factor. High-grade embryos have been associated with higher pregnancy rates. For example, in bovine studies, the quality of embryos (graded on a scale) was directly correlated with pregnancy per embryo transfer (P/ET) rates, with higher quality embryos resulting in better outcomes (Ferraz et al., 2016). Similarly, in equine and ovine studies, the age and developmental stage of the embryo at the time of transfer were significant predictors of successful pregnancy establishment (Currin et al., 2022). 5.3 Environmental and management conditions Environmental and management conditions, including season, temperature, and stress levels, significantly influence embryo transfer success. Heat stress, for instance, has been shown to reduce the number of viable embryos and lower pregnancy rates in cattle (Chebel et al., 2008; Tandulwadkar et al., 2019). Proper management practices, such as the use of heat abatement systems and minimizing stress through adequate facilities, are essential to optimize the conditions for both donors and recipients. 5.4 Role of nutrition and veterinary care Nutrition and veterinary care are fundamental to the success of embryo transfer programs. Adequate nutrition ensures that both donor and recipient animals are in optimal condition for reproduction. For example, prepartum
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