Congratulations on the new babies!!! Do you do a fertility test on all your chickens? Didn't even know you could do that!
I've done fertility testing on most of my hens and I do make it a point to see how well the roos perform too.
There is a facility here in town where you can bring your eggs for fertility testing, not sure about how the test is performed exactly. I just know somebody who's had it done is all. I usually do what Ron said and throw some in the incubator. I have such a varied flock I can usually tell who's laying what egg, or in the case of the sexlinks and FBCM's either one of the two laid an egg.