I have seen more than a dozen scenes of blue sheep killed by snow leopard. Most of the killed blue sheep are one with a pair of big horns.

Luke Hunter mentioned this phenomenon in the section of  "snow leopard"  of  "wild cats of the world". :Snow leopards can take down prey weighing 120 kg, and when face with the largest ungulates, snow leopards usually attack adult male individuals.

Why? Some scientists explain the best long-term survival strategy of carnivores: keep the number of hunting groups in a healthy and stable state, and optimize the prey community by hunting only the elderly and defective individuals who have completed the breeding task. He believes that predators have evolved self-discipline, which is formed through repeated genetic trial and error.

I think this theory is applicable to snow leopard. There are not many blue sheep on the Qinghai Tibet Plateau. Assuming that the snow leopard catches mothers or lambs exclusively, the population of blue sheep will continue to become smaller, and eventually the sheep will disappear, and the snow leopard or their offspring will be extinct because of lack of food.

Mathematician useed complex mathematical models to simulate this process and reach the same conclusion. For the snow leopard, the blue sheep is not its enemy, but its food, which will be used in moderation.

Once I saw the snow leopard observing a group of female rock sheep. The sheep were very close, the leopard  waited for more than half an hour, but  didn't attack, and finally the sheep walked away. This may somehow reflected that snow leopard tend to hunt male  sheep.

There are similar phenomena in the hunting behavior of other animals. In Africa, I took the following picture of cheetahs hunting impala. The tour guide told me that most of the animals killed by cheetahs are male. His explanation is that female animals are more careful and alert.

I have observed three times that the snow leopard hunted the female blue sheep, two times by the newly grown snow leopards, and one time by the female snow leopard with three cubs. 

A natural question, where did all the female rock sheep finally go? One possibility is that wolves hunt more. Wolves hunt by chasing for a long distance. Females and cubs may be easier to hunt. Below, a wolf chases a large group of blue sheep on the ridge.