Pisces Ji,
That is a good question. Why Mongolians eat beef besides being Buddhist if Buddha discouraged to eat it?
There is no doubt that the Buddha discouraged to eat beef. I have read in different places in त्रिपिठक where Buddha was discouraging his lay disciples not to kill cows and Bulls.
In one सुत्र, he was saying something like this:
"Don't kill cow, she milks us, regard her as mother."
"Don't kill Bull, he plough and feed us, regard him as father."
This tells us that the people at the time of Buddha in Indian subcontinent used to kill cow for meat.
In one place, we can found him saying how the cow killing religious ceremonies (गौघातक यज्ञ) were started. He was saying,
"Ancient people used to regard cow as their mother. Some greedy corrupted Yogis, when tested cow's milk product, found so delicious and thought its meat should be more delicious. So, they went to the king and said him that if he (the King) sacrificed cow in यज्ञ, he will get a lot of merit. King had immense respect to Yogis, so he did it."
This fact tells us that there used to be cow killing religious ceremonies during Buddha era.
In different occasion, Buddha went to different people, who were performing multi-animal killing ceremony. He explained to them that killing doesn't bear any merit, real merit comes from non violence and purifying one's own mind. They got convinced and said:
"गोतम, These hundred cows are free now. May they graze green-green grasses! May they enjoy their life and have a natural death!?
This means there used to be cow killing religious ceremony for merit, which seems pretty much similar to modern day दशैं, but much worse.
I have given one more example from महासतिपठ्ठान सुत्त in my earlier posting, where he is giving example of a cow butcher while teaching धातुमनसिकार पर्व of कायानुपस्सना. He was saying:
"Like a skillful cow-butcher or his assistant, having killed a cow in a cross-road-square, divides different parts of its body, similarly, a mediator should be skillful to divide and dissect the reality pertaining to one."
This also supports the fact that people used to eat cow at the time of Buddha.
Contd...