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Defining differences in poultry diets

Jennifer Earing, PhD, PAS, TFC Nutritionist 4/27/2015

For chickens and other poultry, the digestive process needs a little help. When the birds consume feed, it enters the mouth and mixes with saliva.  As feed is swallowed, it travels down the esophagus to the crop, a part of the food pipe at the base of the neck where the initial stages of digestion occur. In natural settings, poultry need to quickly consume a large quantity of feed and then move to a safe location to digest it.

From the crop, the feed moves into the proventriculus.  Digestive enzymes and acid are secreted and begin to digest the feed.  Unfortunately, the acidic environment of the proventriculus is not enough to fully digest large particles of feed like grains or fibrous materials like grass.  As a result, the undigested material moves into the ventriculus, also known as the gizzard.  The walls of the gizzard are very tough and muscular.  These muscles, with the help of small rocks, or grit, mix and grind the undigested feed into smaller particles that can be digested. 

Free-range birds will often pick up small stones from the ground; however, confined poultry should be offered grit to aid in the digestion process.  This is particularly important if the birds are consuming whole or cracked grains or greens like grass and lettuce.  The grit will remain in the bird’s gizzard until it is small enough to pass through the remainder of the digestive tract. 

There is often confusion around the use of grit, limestone (calcium carbonate), and oyster shells in poultry diets.  Grit, often granite or quartz, offers no nutritional benefit other than the mechanical action of grinding up undigested feed.  Grit comes in small, medium, and large sizes for starting, growing, and finishing poultry, respectively.  Young chicks should be started on grit by sprinkling it on their feed twice a week.  Growing chickens and hens should be provided grit free-choice in a feed pan or trough.  While it is not necessary to supplement grit to birds consuming a mash, crumble, or pelleted feed, it does no harm. 

Limestone is offered to poultry as a source of calcium.  While it can provide some grinding action, it dissolves and is absorbed before the undigested feed is completely ground.  Laying hens have increased calcium requirements due to egg production.  It is often necessary to provide supplemental calcium in the diet, even if a well-fortified feed is provided, to ensure adequate eggshell strength.  This can be done by providing free-choice limestone to laying hens.

Oyster shells are also a good source of supplemental calcium and can be offered free-choice to laying hens.  Like limestone, oyster shells provide little grinding assistance in the gizzard.  It should also be noted that free-choice calcium supplements should not be provided to young, growing birds.  Too much calcium can cause weak bones during development.

While limestone and oyster shells offer the same benefit of calcium supplementation, they should not replace grit in the diet.  Grit is particularly important to birds consuming scratch — or whole — grains or greens.  Co-op offers all three supplements: Gran-i-Grit (#1306), Limestone [Coarse Grind] (#1308), and Oyster Shell [Pullet Size] (#1307), in addition to a full line of complete poultry feeds and scratch grains.

For help in assessing your bird’s diet, visit with the feed representative at your local Co-op.

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