How Do Pigs Digest Cellulose?

Pigs are not renowned for being fussy eaters, and will happily grunt and groan their way through anything from a rotten apple to human flesh. Ironically, cellulose, which is the core ingredient in the traditional foodstuff of other domestic animals such as horses, sheep and cows, cannot be easily digested by pigs because they lack the required enzymes to break it down. Most livestock are called ruminants because they have complex digestive systems and four stomachs. Pigs, like people, are monogastric animals, and have only one stomach.

  1. What is Cellulose?

    • Cellulose is considered to be the earth's most common organic compound and is the main structural ingredient of plants. It is commonly associated with grass and hay, but can also be found in cruciferous vegetables such as cabbage, brussels sprouts and even potatoes. Although monogastric animals can absorb the vitamins, proteins, minerals and complex carbohydrates found in vegetables that contain cellulose, the nutrients found in cellulose are inaccessible to their digestive process and are purged directly from the body.

    The Pig's Digestive System

    • Most farm pigs are fed grain. Pigs chew their food, so it is already broken down before it enters their digestive systems. Upon arrival in the stomach, acids and enzymes transform what is eaten into a paste-like material. The half-digested feed is then transferred to the small intestine, where more enzymes complete the digestion process. The majority of nutrients are absorbed from the pig's gut, which is similar to that of a human. At one end of their stomach, pigs possess a small sac called a fundus that provides shelter for a small number of micro-organisms, which break down a little bit of fiber in the pig's diet and allow it to be digested. Ruminant animals can digest much more fiber than pigs or poultry because they support a larger microbial population.

    Pigs Who Eat Cellulose

    • Although cellulose could be viewed as a cheap alternative to the growing expense of pig feed, pigs cannot digest it well, and in the long term it is detrimental to their health. Pigs will eat almost anything, but to grow to their full potential they need a concentrated grain diet and adequate protein supplements. Cellulose is concentrated fiber, and although it may enable other foodstuffs to pass through the pig's digestive tract in a fast, efficient manner, it will not satisfy the hog's hunger or needs.

    The Future

    • Questionable research has been taking place at Taiwan's Institute of Animal Science and Technology to genetically modify a pig of the future that can digest cellulose. Genes from microbes and cows are inserted into pig embryos to create a special breed of pig that can gain its nutrition from grass. Although these pigs have been described as "environmentally friendly" and "cost effective," they are subjects of much controversy.