Corn, or maize, is a primary agricultural commodity used globally as a source of concentrated energy in both human and animal diets. Its high starch content makes it a valuable feedstuff, but the nutritional benefit an animal receives varies widely. This variability results from the kernel’s physical and chemical composition interacting with the specific digestive machinery of the animal. The ability to extract energy from corn depends entirely on whether an animal possesses the anatomical structures or microbial partners necessary to break down its protective layers.
The Structure of Corn and Digestive Requirements
The corn kernel is a highly protected seed designed to resist digestion until conditions are suitable for germination. Its primary structural challenge is the outer layer, known as the pericarp or hull, which is composed mainly of cellulose. Most animals, including humans, lack the enzyme cellulase needed to break the bonds in cellulose, meaning this fibrous shell often passes through the digestive tract largely intact.
Inside the protective hull, the endosperm contains the energy source: starch, which makes up about 75% of the kernel. This starch is stored in semi-crystalline granules and is often encased within a dense protein matrix. Both the crystalline structure and the surrounding protein barrier limit the accessibility of digestive enzymes, specifically amylase, which breaks down starch into simple sugars. Efficient corn digestion requires either a microbial system to handle the cellulose and protein matrix or mechanical/thermal disruption of the kernel structure to expose the starch to the animal’s own amylase.
Animals with Highly Efficient Digestion
Animals that demonstrate the most efficient digestion of corn utilize one of two distinct strategies: microbial fermentation or specialized enzymatic processes. Ruminants, such as cattle and sheep, rely on their multi-compartmented stomach, the rumen, which houses vast populations of specialized microbes. These microorganisms produce cellulase and other enzymes that break down the fibrous hull and the protein matrix, making the entire kernel available for digestion.
The ruminal environment allows for the slow and continuous fermentation of both the cellulose fiber and the starch, converting them into volatile fatty acids that the animal absorbs for energy. This microbial predigestion bypasses the structural defenses of the kernel, resulting in high overall nutrient extraction from the corn grain. However, even in ruminants, the crystalline structure of the starch means that some mechanical processing is often required to maximize the rate of starch breakdown by the rumen microbes.
Optimized monogastrics, including pigs and poultry, employ a different method focused on starch utilization. These animals possess high levels of the enzyme amylase, which is effective at breaking down exposed starch. Their digestive efficiency is heavily dependent on the physical disruption of the kernel, typically through mechanical grinding, which increases the surface area for enzyme access.
Poultry have a short digestive tract and rapid feed transit time, meaning they must break down nutrients quickly. When corn is finely ground, the starch digestibility in pigs can increase significantly, from approximately 89% to over 96%. This strategy focuses on maximizing the enzymatic breakdown of starch in the small intestine, assuming the fibrous hull is mechanically broken before ingestion.
Animals with Inefficient Digestion and Associated Risks
Animals that lack a specialized microbial fermentation system and consume whole, unprocessed corn kernels are susceptible to inefficient digestion and associated health problems. Hindgut fermenters, such as horses, are a prime example; their small stomach and short small intestine are poorly suited to handle large amounts of concentrated starch. When a horse consumes a large quantity of corn, the starch often exceeds the digestive capacity of the small intestine and “spills over” into the hindgut.
In the hindgut, resident microbes rapidly ferment this unexpected influx of starch, leading to an overproduction of lactic acid. This lowers the pH of the gut environment, a condition known as hindgut acidosis. The resulting shift kills off beneficial fiber-digesting bacteria, leading to the release of toxins and gas production, which are major causes of severe intestinal distress, including colic and laminitis.
For pets like dogs, whole corn kernels present a different problem: nutrient waste. Dogs, like humans, are monogastrics that lack cellulase to digest the fibrous outer hull. If the kernel is swallowed whole, the protective shell prevents the dog’s amylase from reaching the starchy interior. Consequently, the entire kernel passes through the digestive tract undigested, leading to the familiar sight of whole corn in the stool and a loss of potential energy.
How Processing Affects Digestibility
The biological limitations of corn digestion can be mitigated or overcome through various processing techniques. Mechanical processing, such as grinding or dry rolling, aims to physically fracture the kernel, breaking the pericarp and reducing the particle size. This action increases the surface area of the starch-rich endosperm, allowing digestive enzymes or microbial populations faster and greater access to the interior.
Thermal processing methods, most notably steam flaking, are more effective because they combine heat, moisture, and mechanical force. In this technique, corn kernels are subjected to steam, which softens the hull and initiates gelatinization. Gelatinization involves the irreversible disruption of the crystalline structure of the starch granule, making it highly soluble and immediately accessible to amylase enzymes.
The steamed kernels are then passed through heavy rollers to create a thin flake, which further disrupts the protein matrix that encapsulates the starch. Steam flaking can increase the digestibility of starch in cattle to over 90%, enhancing the energy value of the feed. This advanced processing essentially pre-digests the corn, allowing animals with less robust digestive systems to efficiently utilize the starch content.