Palpating/Follicle question

I have two females that have been bred to and locked with (on several occasions) two of my males this year. I have tried palpating them for follicles, but have not yet felt any follicles. At what point in the season do you normally start to notice follicle developement? I am new to this, so my palpating skills are certainly going to be sub-par. Any advice?

Thanks in advance!

http://www.youtube.com/watch?v=VDPZ1qSpca8

Thanks...I think i have seen that Ralph Davis vid, but I unfortunately can't watch youtube here at work. I'll be sure to check it out from home!