stoped laying

we have had 11 girls for a year now and 10 of the 11 used to lay on most days, 6 weeks ago we gradualy introduced 8 more young girls. they still have the occasional squable but mainly they seem to get on, the trouble is that most of the older girls have stopped laying, (5 of the new girls are laying ) any advice on how to get the old girls laying again
thanks in advance
desandchez

i had some very good advice from this site, have you checked them for crawlies, and do you worm them regularly? my chickens stopped laying and i thought it was becuase of the ducks!, didn't see any crawlies an them but doused them anyway and today had 3 eggs (only have 4 hens) whereas i was only getting an egg from them in a week! might  be worth doing them all anyway 

Hello there! if my egg numbers drop! then i revoke all treats and just feed layers pellets! someone advised me to do this last year and it worked a treat, although it does sound like they are just in protest at the new arrivals! good luck