Excuse me, what does "a thousand cows in the East Palace prepare for their lives" mean?

Niu Qian is an official position. In the Northern Wei Dynasty, the Northern Qi Dynasty and the Northern Zhou Dynasty, Niu Qian was established to take charge of the imperial sword. Leading the left and right houses, so it has the name of a thousand oxtails. Also known as "Battle of Thousands of Cows", he held an imperial knife as a guard around the emperor. Niu Qian is the name of this sword. In the Tang Dynasty, the left and right Niu Qian Guards were set as one of the Guards, and their subordinate officers prepared for Niu Qian. Seinfeld

"The position of a thousand cows in the East Palace" refers to the position of a thousand cows in the East Palace of the Prince.