Carbohydrates - Structure & Digestion

Study Notes

Carbohydrates are primarily composed of carbon, hydrogen, and oxygen.
They are the primary dietary energy source for animals.
The basic building block of carbohydrates is a monosaccharide, examples include glucose, fructose, and galactose.
Disaccharides are formed by the combination of two monosaccharides, examples include sucrose and lactose.
Polysaccharides consist of three or more monosaccharides.
Starch and cellulose are the two main types of polysaccharides found in animal diets.
Starch molecules are linked by alpha linkages that can be broken down by both mammalian and microbial enzymes.
Cellulose molecules are linked by beta linkages, which can only be broken down by microbial enzymes.
Grains are high in starch, while forages are high in cellulose.
Other carbohydrates like pectins and hemicellulose are only digestible by microbes.

Monogastric animals primarily digest starch in the small intestine using pancreatic amylase and other enzymes.
Monosaccharides are readily absorbed into the bloodstream via the small intestine.
Some monogastrics, like horses, can utilize forages due to microbial populations in their digestive tracts.
Horsesh have the highest utilization efficiency of fibrous compounds among monogastrics.
Ruminants primarily digest carbohydrates in the reticulorumen.
Rumen microbes digest sugars, starch, hemicellulose, and cellulose.
Volatile fatty acids (VFAs) like acetic acid, propionic acid, and butyric acid are the main end products of rumen fermentation.
VFAs are absorbed in the rumen or small intestine and metabolized to produce energy.
High starch diets result in higher propionic acid production, while higher fiber diets lead to more acetic acid production.
Intestinal digestion of carbohydrates is limited in mature ruminants.

Methane is a major component of natural gas and a greenhouse gas.
Rumen gas contains approximately 30-40% methane, along with CO2, H2, and small amounts of O2 and nitrogen.
Approximately 4.5 grams of methane is produced for every 100 grams of carbohydrate digested, representing a 7% energy loss for the ruminant.
Adding unsaturated fatty acids to the diet can reduce methane production by providing hydrogen for saturation by microbes.

Alkali treatment can increase the degradability of crude fiber.
Grinding roughage can reduce digestibility by as much as 20%.
Pelleting roughage can decrease crude fiber digestion due to increased rate of passage.