Here is how I deal with the property with out reloading them for every screens. You ought to load your asset in your essential sport class like this

public class MyGame extends Game {
    personal AssetManager assetManager;

    @Override public void create() {
        this.assetManager = new AssetManager();

        this.assetManager.load("degree.tmx", TiledMap.class);
        this.assetManager.load(...)
        this.assetManager.load(...)

        // power the asset supervisor to complete loading
        this.assetManager.finishLoading()

        // inject the asset supervisor to your display screen
        this.setScreen(new LevelScreen(this.assetManager));
    }

    @Override
    public void dispose() {
        this.assetManager.dispose();
    }
}

This approach if I have to reload the LevelScreen I simply have to re inject the assetManager to the brand new display screen with out reloading any ressources.

To retrieve a useful resource from the asset supervisor, simply use

// this retrieve the tiled map from the asset supervisor with out reloading it
TiledMap levelMap = assetManager.get("degree.tmx");