The chicken came first! Old mcdonald raised this chicken.
Old Macdonald had a farm, E-I-E-I-O
And on his farm he had a chicken, E-I-E-I-O
As you can see, Chicken Obviously was raised and bred by Old Mcdonalds, it even indicates it in the song.
In the song their is no mention of the egg, but it does mention the chicken.