A chicken’s digestive system is very different from humans.
The main difference is that they have crops and gizzards, both of which have important roles and affect greatly the efficiency with which chicken can get the most out of the feed they eat. Both have evolved over millions of years during which the ancestor of chicken, the Indian Jungle Fowl lived in the dim, humid and hot conditions of ancient jungles.
In the jungle there were and still are many predators looking for a chicken dinner! So when the Jungle fowl eats it has to eat very quickly and then fly up into the jungle canopy before it gets eaten itself. The survival of the fittest led to a food storage system, known as the crop. The food in the crop, consisting of plant material, insects, berries and seeds, formed a porridge like mass, which gradually emptied further down the gut until empty. The crop was filled twice a day, first early in the morning, before the heat of the day and after the sun had gone down in the cooler evening. During the time the food was in the crop, the cells of the plant material soaked up water (there is a lot on the jungle floor) and swelled up. The swelling of the plant cells burst the cell walls, which released their contents for better digestion in the lower gut.
The soaked food then passes slowly to the next organ, the gizzard, which is a very muscular grinding organ. Its function is to grind the hard grains, seeds and hard-shelled insects into much smaller particles so that the digestive juices secreted in the lower gut can get at the starches and proteins. The smaller the particles the bigger the surface area for the digestive enzymes to work on, so evolution led to very efficient gizzards, which with the crop, enabled the most value to be extracted from the food eaten.
The effect of Intensive housing (post 1950’s)
Before this, chicken were kept on free range, and fed twice a day including some whole grains. So the crop and gizzard were fully functional, which ensured very efficient use of the food eaten. But when intensive housing started, things changed dramatically.
Old feeding equipment such as tube feeders, cable and flight systems and chain feeders led to ad-lib feeding, which is unnatural for the birds. All feed was produced in compound feed factories, where all the whole grain components were put through hammer mills. So there were no whole grains for the gizzard to grind. So two important organs, which chicken had evolved were redundant, and made no contribution to digestion.
FLOCKMAN restores digestive efficiency to the modern broiler, resulting in the better feed efficiency seen, as well as Health and Welfare benefits to the birds.