One should do his "VARNA ASHRAMA DHARMA" by knowing the (Dharma) SHAASTRAM-Srimadh Bhagavath Gita

Ahimsa: Impact of Buddhism on Hinduism?.NO!

Diet of hindus was mainly vegetarian since time immemorial. Consumption of beef is prohibited. But consumption of meat etc is accepted only as prasad (Yagya Shaesha) after ritulas that too in very small quantity during 'special occasions'. Non-veg is NOT advocated for daily diet. Saying Change of culture after advent of Jainism & budhhism is unacceptable.

Did brahmins eat beef in sacrifices ?

NO. They did not eat. They should not eat beef.

BUT, they have to consume a small quantity (mustard size) of goat meat as 'Prasad' of Devathas to make the sacrifice fruitful. IF they refuse, it is considered as humiliating Devathas & the sacrifice become futile. It is COMPULSORY to take meat of Goat as prasad after offering to devathas!.

So, understand that brahmins didn't eat heaps of beef after sacrifice.

Were cows slaughtered for sacrifices?

NO. 'Pashu' in sanskrit means animals in general. In ritual scriptures it means GOATS. NOT COWS. Wherever we see that so many pashus were sacrificed in rituals we need to understand that it was goats. No where in scriptures it is said to sacrifice cows.

So understand that  hindus did not kill cows!. eg. In 'Pashu bandha' ritual  goats should be sacrificed. Not cows.Similarly in Somayagas like Yajapeya etc.