In Act IV scene 1 Antony says the following of Lepidus:

"ANTONY:
Octavius, I have seen more days than you:
And, though we lay these honors on this man,
To ease ourselves of divers slanderous loads,
He shall but bear them as the ass bears gold,
To groan and sweat under the business,
Either led or driven, as we point the way;
And having brought our treasure where we will,
Then take we down his load and turn him off,
Like to the empty ass, to shake his ears
And graze in commons."

Basically, Antony is comparing Lepidus to a beast of burden, specifically an ass (or a donkey). He says that Lepidus, though one of the new leadership, is really nothing more than someone to use--to bear the burden of the slander that may fall upon the new leadership, and then be rid of once he has served his purpose. Antony obviously has little respect for Lepidus and only wants to use him.

When Octavius points out that Lepidus is a "tried and valiant soldier," Antony further compares him to his horse:

"So is my horse, Octavius;and for that
I do appoint him store of provender:
It is a creature that I teach to fight,
To wind, to stop, to run directly on,
His corporal motion govern'd by my spirit.
And, in some taste, is Lepidus but so;
He must be taught, and train'd, and bid go forth:
A barren-spirited fellow; one that feeds
On objects, arts, and imitations,
Which, out of use and staled by other men,
Begin his fashion: do not talk of him
But as a property.

Antony contends that Lepidus is too weak to be a real leader, that, like his horse, he is only good for being led and taught by stronger men (like Antony). He then tells Octavius to only think of Lepidus as "property."

A complete side-by-side text of Julius Caesar with both original and modern translation is available through Enotes