First, in the 20th century, the number of male giant pandas that could participate in breeding was rare. At that time, there were about 120 male pandas in China and abroad, and only one was able to participate in natural mating.
Second, it is difficult for male pandas to come into estrus. Female pandas entering the breeding season in captivity can generally come into heat on a seasonal basis, but males are difficult to come into heat, and artificial insemination was also used as a supplementary method at that time. But female giant pandas can conceive only about three or four days in a year, and there are no obvious physiological characteristics. Therefore, in artificial insemination, it is difficult to accurately grasp their ovulation period. For example, in 1989, 18 female giant pandas were either artificially inseminated or mated naturally, some were even given both methods, but only 6 were conceived.
Third, it is difficult for the cubs to survive. A newborn cub is only the size of an ordinary mouse and weighs about 100 grams, one-thousandth of the weight of an adult panda. In mammals, except marsupials, there is no animal with such a disparate size ratio between mother and child. The cubs have closed eyes, can't see anything, and have only sparse lanugo on their skin. Their level of development is about the same as that of a six-month-old human embryo, and their kidneys, brain and some immune organs and lymphoid tissues are not fully developed. This kind of organism may have adapted to the environment of high mountains, ice and snow, where there were rarely any bacteria, but it cannot adapt to the ex situ environment. Giant pandas have low mating rate, low conception rate and low survival rate, and these are their particular challenges among captive animals. This "three lows" was the problem of breeding giant pandas at that time