Overview
Limestone (calcium carbonate) is the primary source of inorganic calcium used in feed mills, serving as a vital macro-mineral for skeletal development and eggshell formation. Because calcium is required in high quantities but cannot be fully provided by grains or oilseeds, limestone is a fundamental, high-volume ingredient in almost all feed formulas.
Applications
- Eggshell formation — in laying hen diets, calcium is the critical component needed to produce strong, crack-resistant eggshells.
- Bone mineralisation — provides the structural foundation for skeletal growth in young broilers, piglets, and calves.
- Metabolic regulation — supports crucial physiological functions including blood clotting, muscle contraction, and nerve impulse transmission.
Categories
Particle size in feed milling
- Fine powder (0.1–0.4 mm) — used for broilers, swine, and calves; the small particle size allows rapid digestion and absorption in the gastrointestinal tract.
- Coarse grits (2.0–4.0 mm) — essential for laying hens; dissolves slowly overnight in the gizzard, giving a steady calcium release during eggshell formation and sparing the hen’s own bones.
Feed mill handling & quality control
- Abrasiveness and equipment wear — limestone is highly abrasive; mills must use hardened steel for augers, mixers, and die plates to prevent rapid machinery degradation.
- Calcium concentration verification — feed-grade limestone must contain 36%–38% pure calcium; regular lab testing ensures it is not diluted with sand or silica.
- Heavy metal screening — geological variation means it must be screened for lead, arsenic, and fluorine to prevent livestock poisoning.
- Flowability — fine powder absorbs moisture and can bridge or cake in micro-bins and silos, often requiring vibratory dischargers or fluidising pads.