Hi, my girls are at the 17-week mark now and have been getting the Dumor grower/finisher feed since about 10 weeks. I have quite a bit left in the big feed bag, but starting next week they should be getting the layer mix. Is it okay to just finish the bag and when it's done start the layer mix, or should I just give away the rest of my grower/finisher mix & start the next stage? Also, the feed bag says that you don't need to supplement w/ oyster shells...the feed provides all the necessary nutrients for egg-laying...is that true, or should I give the oyster shells anyway. Any feedback would be very welcome! Thank you!