1 yr.old hens not laying

[Feather's McGraw]

I replaced my flock in September '09 with new chicks, thinking that by spring '10 they would start laying. I have 6 Rhode Island reds, 6 Buff Orp. , 6 Barred Rock, 3 Araucana, and 2 Wyndots. Out of 23 hens, we have been getting only 12-13 eggs a day. Now, they are starting to lay about 6-7 a day. We have 5 nest boxes and they are in a 50'x20'outdoor area during the day. At night they roost in the hen house which is 6x8 and has several roosting posts. They are free to eat and drink as much as they like. The flock that I replaced laid eggs very well, they just got old. Not sure what the problem is and if I should buy new chicks and start over again.