Nutrient absorption stands as a fundamental process for all living organisms, allowing them to extract essential components from their diet. For pigs, this process is particularly important, directly influencing their growth, development, and overall health. A pig’s digestive system is designed to efficiently break down ingested food, converting complex feed ingredients into usable forms for the body.
An Overview of Pig Digestion
The journey of food through a pig’s digestive system begins with ingestion, where feed enters the mouth and undergoes initial mechanical breakdown through chewing and enzymatic digestion from saliva. From there, the food travels down the esophagus, a muscular tube that propels it towards the stomach. In the stomach, strong acids and enzymes continue the breakdown process, creating a semi-liquid mixture known as chyme.
This chyme then moves into the small intestine, where the majority of digestion and absorption occurs. Following its passage through the small intestine, any remaining undigested material enters the large intestine. The large intestine processes waste products, and finally, undigested material is eliminated from the body through the rectum and anus.
The Small Intestine: Main Nutrient Absorption
The small intestine is the primary site for the absorption of most nutrients in a pig, accounting for the uptake of the vast majority of digestible carbohydrates, proteins, fats, vitamins, and minerals. Its specialized structure maximizes the surface area for nutrient uptake. The inner lining of the small intestine is covered with numerous small, finger-like projections called villi. These villi, in turn, are covered with even tinier projections known as microvilli, collectively forming a “brush border.” This extensive folding and projection system significantly increases the absorptive surface area, which can be as large as 40 square meters in an adult pig.
Carbohydrates, broken down into simple sugars like glucose, are absorbed primarily through active transport mechanisms across the intestinal wall. Proteins are digested into amino acids and small peptides, which are then actively transported into the bloodstream. Fats, after being emulsified by bile and broken down by lipases into fatty acids and glycerol, are absorbed into the lymphatic system before entering the bloodstream. Most water-soluble vitamins, such as B vitamins and vitamin C, and fat-soluble vitamins (A, D, E, K) are also absorbed in the small intestine, often with the help of specific transporters or micelles. Over 90% of digestible nutrients from a pig’s diet are absorbed within this segment.
Other Absorption Zones
While the small intestine is the main site for nutrient absorption, other parts of the digestive system contribute to the overall process. The stomach, for instance, is primarily involved in the initial breakdown of food through acid and enzyme action. Limited absorption occurs here, mainly confined to water, some simple salts, and certain fat-soluble substances like alcohol or specific medications.
The large intestine, comprising the cecum and colon, plays a different but important role in nutrient recovery. This segment is not a major site for the absorption of complex macronutrients, as most of these have already been absorbed in the small intestine. Its primary functions include the absorption of water and electrolytes, which helps to consolidate the digesta and prevent dehydration. The large intestine hosts a diverse population of microbes that ferment undigested feed components, particularly fiber. This microbial fermentation produces volatile fatty acids (VFAs) such as acetate, propionate, and butyrate, which can be absorbed through the large intestinal wall and serve as an energy source for the pig.