Title:Advancing Asian Elephant Reproduction through Artificial Insemination: Potential Artificial Insemination Outline
In the past decades, Asian elephant population throughout the world has been declining at an alarming rate, in which they have been listed by CITES as endangered species since 1972. Many efforts have been made to improve Asian elephant breeding both in the wild and in the captive populations. Even though natural mating has a higher conception rate, it is not self-sustaining due to several factors. Artificial insemination (AI) has been introduced to enhance the reproduction rate, especially in captive population. With self-sustaining captive population, capturing of new animals from the wild to replace the captive ones could be minimized. AI can be advantageous in maintaining genetic diversity from distant mating and in the establishment of gene bank resources. It would also allow sex-sorting of semen, which could contribute to correct the currently shifted sex-ratio in the Asian elephant population. The success of AI can be influenced by multiple factors, such as semen collection method, AI technique, semen type with their extenders and cryoprotectants, cooling, freezing and thawing methods, as well as appropriate timing of AI. Manual rectal stimulation is the recommended method for semen collection, where separated sperm-rich fraction can be obtained without the need for extensive training. A non-surgical-AI technique is suggested, where ultrasound-guided modified endoscopic AI allows for the best visualization of semen deposition site. There is no ideal protocol for semen extenders and cryoprotectants, rather understanding how different substances work to maintain post-treatment semen quality. It was observed that egg yolk contains lipoprotein, which helps to preserve plasma membrane integrity. Additional glycerol was also seen to diminish cryoinjuries by reducing osmotic stress and minimizing the amount of water molecules susceptible for ice crystal formation. Directional freezing was found to result in better post-thaw semen quality, while dry shipper has the potential to be used in cryopreservation. The timing of AI was suggested on day 0 or day 1-2 after ovulation, which occurs 24 h after ovLH surge. Nonetheless, there are still high variation and inonsistency in the semen quality and quantity between bulls and within an individual, making it challenging to set up a standardized AI protocol in Asian elephants.