Cation exchange capacity
Cation exchange capacity (CEC) is a plant’s ability to attract and bind hydrogen ions. When hydrogen ions are bound to plant matter rather than free in the rumen, the rumen is less acidic.
Alfalfa, citrus pulp, and beet pulp are all good sources of pectin having high CEC.
It is well known that rumen pH is affected by the amount of fiber in the diet as well as its length of cut. Long, effective fiber stimulates cud-chewing. Cud-chewing produces saliva which buffers the rumen and decreases rumen acidity. Chemical properties of the diet can also affect rumen acidity. The term "cation exchange capacity" (CEC) refers to a plant's ability to attract and bind hydrogen ions. High concentrations of free hydrogen ions in the rumen cause high rumen acidity. Hydrogen ions have a positive charge. Plant cells generally have many negative charges on their surface and will bind hydrogen ions. If the ions are chemically bound to the plant rather than free, the rumen will become less acidic. Some plant cells have more negative charges than other plant cells.
Studies have been conducted on different types of plants to determine their cation exchange capacity. The higher the cation exchange capacity, the better the plant will be as a rumen buffer.
Cation Exchange Capacity of Some Common Feeds and Other Plants
||Cation Exchange Capacity (mmol/kg cell wall)
Cellulose has a low CEC while pectin has a high CEC. Cellulose is the slowly digestible fiber that is in the ADF along with lignin (which is indigestible). Pectin is the soluble, rapidly digestible fiber that is not included in the ADF or NDF fraction of feed. Although it is a fiber, pectin is included in the non-fiber carbohydrate (NFC) fraction in traditional feed and forage analysis. Alfalfa, citrus pulp, and beet pulp are all generally good sources of pectin.
Has the impact of CEC ever been apparent on commercial dairy farms? It’s hard to say. There may have been times when we have seen less acidosis when cows have been fed alfalfa and beet pulp rather than grasses at the same length of cut. Unfortunately, there have been other confounding factors. No controlled research studies are known to have looked at the effect of CEC on acidosis in lactating cows.
One other advantage of a high CEC in plants is that it also increases the rate at which the rumen microbes digest the feed. Minerals with two positive charges, such as magnesium, will actually bond with the negatively charged plant cell and the negatively charged microbe. This attachment allows the microbes to concentrate their enzymes on the feed cell and to be close to the release of soluble nutrients from the plant cell. Thus, the microbes grow faster and the rate of digestion of the plant cell is increased.
McBurney, M.I., P.J. Van Soest, and L.E. Chase. 1983. Cation exchange capacity and buffering capacity of neutral-detergent fibres. J. Sci. Food Agric. 34:910
Russell, J.B. 1988. Microbiology of the Rumen. Animal Science 607 Class Notes, Cornell University.