Are these sentences interchangeable? (pseudogapping)
And if so, which one is preferred over the other?

They have been eating the apples more than they have been eating the oranges.
They have been eating the apples more than they have the oranges.

Similarly, are "I will feed the chickens today if you will feed the chickens tomorrow" and
"I will feed the chickens today if you will chickens tomorrow" interchangeable?

Question

Are these sentences interchangeable? (pseudogapping)
And if so, which one is preferred over the other?

They have been eating the apples more than they have been eating the oranges. 
They have been eating the apples more than they have the oranges.

Similarly, are "I will feed the chickens today if you will feed the chickens tomorrow" and
"I will feed the chickens today if you will chickens tomorrow" interchangeable?

Answer

These 3 are English sentences, the first 2 are interchangeable and mean the same 
thing.
They have been eating the apples more than they have been eating the oranges.
They have been eating the apples more than they have the oranges. 
I will feed the chickens today if you will feed the chickens tomorrow

The next one is not an English sentence.
I will feed the chickens today if you will chickens tomorrow

I will feed the chickens today if you will tomorrow <-- this is the sentence that you want.

Answer

할아버지 감사합니다. ^0^  It seems crystal clear now.

Answer

more contracted ... "They have been eating the apples more than the oranges" or even more succinct, "They have been eating more apples than oranges."