The purpose of the present study was to examine the extrusion-cooking process of cereal blends with addition of hatchery waste (HW). The effect of HW addition on the physical properties and chemical composition of the extrudates was examined. The share of the HW in blends with corn meal was variable in the range of 5–30%. The study was conducted using a counter-rotating twin-screw extruder (L:D ratio 12:1, screw speed 75 rpm, die diameters 3 mm × 6 mm, profile of barrel temperature 120/140/180/180/130°C, and material moisture 28%). Increase in the content of the HW from 5 to 30% reduced the expansion ratio, pellet durability index, water absorption index, and water solubility index of the extrudates. The microstructure of the extrudates with HW addition is non-homogeneous; the areas with densely packed and adherent granules, interwoven with fibrous structures, can be observed. Increase in the share of HW leads to a lowering of the levels of crude fiber and total dietary fiber in the extrudates. Moreover, a significant increase in the content of protein, crude fat, and mineral elements such as calcium, sodium, magnesium, and iron was observed.