Combine Two RSS Feeds to Appear as One in PHP

[lonestar23]

How would I go about combining two seperate rss feeds to appear as one list in PHP?

example:
abc.com/horse/rss
monty.com/cow/rss

=== results ===
1.) lovely horses
2.) great looking cows
3.) my pony is sick
4.) cows make good steaks
etc....

Thanks in Advance!