Great question, flockoffour! Chickens store fat differently than most animals. Many animals will actually store fat within the muscle, which is often referred to as “marbling.” Chickens don’t store fat in the muscle (this is why it is a lean meat), they store their fat between the skin and the muscle. However, the majority of their fat is stored in the “fat pad,” which is found between the legs on the underside of the chicken.
One way to determine if your hen is too fat is to feel for the pubic bones of the chicken with your fingers. These bones come to a point on either side of the vent. When the hen has little fat stores, these will be very easy to find and will be pointed. As the hen’s fat stores increase, the pubic bones will be harder to find and will not feel as pointed. This is because there is now a layer of fat between the bones and the skin.
To help keep your birds healthy and trim, follow the 90/10 rule; 90% of the diet should be a complete feed and no more than 10% of the diet should consist of treats and scraps.
Read here for more information on feeding treats and scraps. Treats & Snacks: Are They Good for My Hens?