What are ISO's?

I'm guessing they are talking about an ISA, probably ISA Brown. That is a type of commercial laying chicken. They have been bred to lay a lot of large eggs early in the commercial situation. They have a relatively small body so they are more efficient at using the feed to make eggs instead of using it to maintain a large body like the RIR, for example.

One possible drawback, they can burn out after a hard year of laying eggs. Thye are specialized chickens, specially bred for commercial laying operations which replace their chickens after their laying cycle. They are not bred for longevity. If you watch their feed a bit and don't overfeed them, they have a better chance of lasting through extra seasons and still laying great.

Many people get them and love them. It depends some on your goals.

 

An ISO is a cross between a Buff Orpington and a Rhoade Island Red.

 

Mine are ISO brown. They do lay larger eggs. Lots of double yolks and even a triple here and there! They are consistent in number but not in size.

How long is the egg production expectation of the ISO, since you say it's shortened?