Where in the gizzard is the mechanical grinding of feed ingredients facilitated by insoluble grit?

The avian gizzard, or ventriculus, is a highly specialized muscular organ designed to mechanically grind feed particles in the absence of teeth. This grinding process takes place within the central cavity of the ventriculus, which is lined with a tough, yellowish-brown membrane made of Koilin—a complex protein-keratinized polysaccharide mixture secreted by the underlying glands. When the bird swallows insoluble grit (such as granite or quartzite stones, 2.0 to 4.0 mm in size), these stones become trapped within the koilin lined cavity. The massive, opposing muscular contractions of the gizzard's lateral muscles grind the raw feed grains directly against this abrasive grit, crushing tough seed coats and fibrous NSPs before enzymatic digestion in the intestine. Farmers can study gizzard physiology in the Poultry Encyclopedia, purchase standardized insoluble granite grit on Poultry Plaza, check grain rates on Poultry Rates, and trade healthy, active layer flocks on Murghi Mandi.