Tigers, just like all cats, are induced ovulates In a natural breeding situation, that means that the male will stimulate the female to ovulate by breeding repeatedly. Once the female ovulates, the egg will drop and have the opportunity to be fertilized. This means that they cannot become pregnant after one breeding attempt. Female tigers generally go into estrus for about 7 days, and the male takes full advantage of that time to increase his chances of producing offspring. Herein lies the challenge. How do scientists replicate this? While this has been more successful in smaller cats, the technique is still in the beginning stages for tigers.
There are multiple ways that AI can be done, but before the big day, there is hormone manipulation. Each female tiger will have their own estrus pattern that is unique to them (similar to humans, the basics are the same, but there are individual differences). To control the timing of this, regumate can be given for 30 days. This is an oral medication that inhibits endogenous ovarian activity to gonadotropins and also increases the follicle-stimulating hormone that stimulates the growth of oocytes- the key to success. It is then timed to pick when the estrus cycle should begin. Once the female is taken off regumate, she should start to show estrus signs. 5 days before the AI procedure is scheduled, the female will receive Equine Chorionic Gonadotropin (eCG) hormone injection. 82 hours after that injection she will receive a second injection of Porcine Luteinizing Hormone (pLH). The timing is key to ensure the tiger is ovulating during the AI procedure.
The simplest, is vaginal AI. This is really just mimicking natural breeding, but eliminating the presence of a male. This method requires a high volume of sperm. To give you some perspective, for a domestic cat 80 million sperm gives about a 75% chance of pregnancy. Vaginal AI with tigers requires a volume of 500 million sperm, and there has only been one pregnancy ever. Uterine AI is where the sperm are inserted past the cervix, which is closer to the oocytes than vaginal. This can be done either surgically or non-surgically, although the surgical version of this is considered the most successful with felids overall. Laparoscopic oviductal AI is a surgical procedure where the sperm are deposited on top of the oocytes, which requires a greatly reduced amount of sperm for tigers.
Although this may all sound very sci-fi, it is the wave of the future for some species. It is our way to ensure genetic diversity while lowering the risk that comes with transporting animals in human care. Male tigers do not participate in the rearing or raising of cubs, therefore removing them from the picture will not change the natural process of raising cubs. If we can help the female tigers become pregnant, they can take it from there!