The ISA people are the largest poultry breeders in the world. Their hybred ISA brown is only 4.3 pounds and has a feed conversion factor of 2.14, meaning that for every 2.14 Lbs of feed they lay, they produce a pound of egg. The heavier sex link birds from other hatcheries can't come close. This is why 60% of the brown egg production in the world is from ISA browns. ISA also produces the Amberlink, a slightly heavier 4.5 Lb hen that is said to do better as a forager or on grain mix's instead of processed feed. Most ISA lines are developed for battery type egg factories, but lay very well in the average henhouse. ISA has also produced production Leghorns that only weigh 3.8 Lbs and far outperform traditional full size leghorns. As the largest breeder of egg production breeders in the world, they have resourses that are beyond the reach of smaller operations. The ISA browns and Amberlink are sold by Hoover, Town Line, and Mt Healthy.