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.

Updates

Dear Readers,

As I do not have enough time to post my views,I have written these Posts in a hasty manner.There may be many grammatical or spelling mistakes for which I apologize!.The posts may seem to be funny & irrelevent to present day to day life to "some people",who may find these posts difficult to digest!.I am ready to explain to them when I find time.Till then,I request readers to do their own research from their side on our scriptures and come to a conclusion.Because,Our Hindu religion is very vast and every thing can't be spoon-fed!.

I am thinking of explaining each & every thought of mine elaborately when I find time.So,do visit this blog for recent updates.