Non-Fiber Carbohydrate (NFC) is made up of starch, simple sugars, and soluble fiber.
Starch digestibility varies according to source and processing. A goal when feeding dairy cows is to have maximum total tract digestion of starch without rumen acidosis
For maximum microbial growth, the availability of carbohydrates and protein must be synchronized. Feeding blends of rapidly and slowly digestible starches is helpful.
Sugars provide an immediate source of energy for the rumen microbes.
Soluble fiber is fermented rapidly in the rumen but yields weaker acids as byproducts. It does not create as much acid as starches and sugars.
Non-Fiber Carbohydrates (NFC) (also sometimes called Nonstructural Carbohydrates (NSC)) usually make up 35-40% of the dry matter in a ration designed for high production. NFC is calculated by difference [100-(%NDF + %CP + %Fat + Ash)]. The Cornell Net Carbohydrate / Protein System defines NFC as [100-((%NDF - %NDF-CP)+ %CP + %Fat + Ash)]. This equation is actually more correct because it doesn’t double-count the protein that is contained in NDF. NFC is generally more rapidly digested than fiber. It is a significant source of energy for the rumen microbes. Volatile Fatty Acids (VFA’s), primarily propionate, are made from the fermentation of NFC. They are absorbed from the rumen and used as a source of energy by the cow. The microbes also use NFC to make microbial protein.
Non-Fiber Carbohydrate is made up of different amounts of starch, simple sugars, beta-glucans, galactans, and pectins. NFC is a non-uniform nutrient fraction. This frustrates nutritionists. Portions of the NFC ferment faster than other portions. Because of this non-uniformity, NFC can ferment very differently depending on its ingredient source, affecting milk production and rumen health.
Most of the NFC in grain-based rations is made up of starch (24-28% of the total ration DM). Cereal grains, such as corn and barley, provide the greatest proportion of the starch in a cow’s diet. Starch is made up of glucose sugar units that are bonded together. Starch digestibility, both in the rumen and intestine, has a crucial impact on milk production. Depending on the starch source and processing, the glucose units may be very tightly bonded and compacted together or they may be weakly linked together. For this reason, different starches may be either rapidly or slowly fermented in the rumen. The rates of starch digestion in the rumen vary from 6-60% per hour, depending on starch source and processing. The goal is to get maximum total tract digestibility and maximum microbial protein production from starches, without adversely affecting rumen health from the build up of fermentation acids in the rumen.
Factors Affecting Starch Digestibility
Rate of starch digestion is known to depend in part on its source.
Fast >------------------Intermediate ---------------------> Slow
Wheat Barley Oats Corn Sorghum
1. High Moisture Ensiling
Ensiling high-moisture grains (28-32% moisture) increases starch digestion by breaking down the protein structure of the grain and disrupting the crystalline structure of the starch. This allows the rumen microbes to more easily burrow into and digest the starch after the grain is consumed.
Grinding increases the amount of surface area that the rumen microbes can attach to. Thus, grinding increases starch digestibility in the rumen and in the intestine. Cornmeal may either be coarsely or finely ground. Finely ground cornmeal will be digested to a greater extent. However, grinding too finely may cause more acidosis. Researchers at Michigan State University increased milk production by 3 pounds/cow/day (from 76 pounds to 79 pounds) when they fed ground corn rather than cracked, dry shelled corn. Milk protein increased by 0.1 percentage unit (from 2.8% to 2.9%) and milk fat decreased by 0.2 percentage units (from 3.7% to 3.5%).
Because of the non-crystalline nature of the starch in high-moisture corn (HMC) (28-32% moisture), it is usually recommended that it be rolled rather than ground. Grinding will usually make HMC degrade too rapidly and cause acidosis. However, sometimes we must deal with HMC that is drier, less than 28-32% moisture. In that case, it must be ground more finely. Miner Institute in Chazy, New York reported an increase of 5 lb/cow/day when corn at 23% moisture was ground with a hammer mill through a 1/2" screen.
Recommended Particle Size of Corn Products (Sniffen et al., 1996)
% Retained on a 1/8" screen
HMC, 21% moisture
HMC, 25% moisture
HMC, 30% moisture
According to Dr. Charlie Sniffen of Miner Institute, Chazy, NY, if the amount of cornmeal retained on the 1/8" screen is only 5-10%, NEl can be adjusted upward by 5%. But, watch out for acidosis with this corn! If 30-35% of the cornmeal is retained on the 1/8" screen, NEl can be discounted by 5 to 10%. Remember, however, that the amount of effective fiber in the ration can impact the amount of energy in the corn. Coarsely ground cornmeal will stay in the rumen longer and be more completely digested if there is a good fiber mat.
3. Gelatinization or “Cooking”
Gelatinization is defined as the irreversible destruction of the crystalline order in a starch granule, so that the surface of every molecule is made accessible to solvents or reactants, including the rumen microbes. Gelatinization in feed is brought about by a combination of moisture, heat, mechanical energy, and pressure. It increases the speed at which enzymes and microbes can break down the linkages of starch to yield energy and microbial protein.
Steam-flaking, steam-rolling, extrusion, and pelleting all cause starch to gelatinize. However, the degree of "cook" is highly dependent on the amount of moisture, pressure, and heat actually obtained during each of these processes. Steam-rolled grain is usually steamed for 10-15 minutes and then rolled. Its density is about 38 pounds per bushel. Steam-flaked grain is steamed for 35-40 minutes and then flaked. Its density is about 25-30 pounds per bushel. Arizona researchers got a 5 pound per day response in milk production when they fed steam-flaked corn rather than steam-rolled corn. In this same study, they also compared steam-flaked corn versus finely ground cornmeal. In one part of the study, cornmeal in the diet produced more milk than the diet with steam-flaked corn (90 vs 88 pounds/day). In the other part of the study, the diet containing steam-flaked corn rather than cornmeal yielded more milk (82 vs 78 pounds/day). Steam-flaking costs more money than grinding corn. Most researchers see little advantage in steam-flaking over grinding, especially when the cost is considered.
4. Chemical Treatment
Sodium hydroxide (NaOH), a caustic chemical, is being used by some farmers to disrupt the protein matrix of grain and to gelatinize starch. It is used on whole grains as an alternative to grinding. However, rumen digestibility of this grain is generally lower than that of ground grains and this may lower microbial protein synthesis.
Synchronization of Energy and Protein Availability in the Rumen
When feeding dairy cows, a primary goal is to make as much rumen microbial protein as possible. Protein from the rumen microbes is high-quality. It contains a blend of amino acids similar to that needed for the production of milk protein. To make microbial protein, it is generally recommended that rations contain 35-40% NFC and 17-18% CP with 60-65% of the CP as degradable protein (DIP) and 30% of the CP (or half of the DIP) as soluble protein (SIP). But, we need to take this recommendation one step further. For maximum growth of the rumen microbes to occur, the microbes need to have energy (from carbohydrates) and nitrogen and amino acids (from protein) available in a correct ratio every minute of the day. If too much protein is supplied without available carbohydrate, the microbes will use the protein as a source of energy and waste the nitrogen found in protein. For example, alfalfa silage and raw soybeans contain a lot of rapidly digestible protein. So, rapidly available carbohydrate needs to be fed with them. Roasting soybeans slows down the rate at which protein is degraded in the rumen so that it will more evenly match the rate at which energy becomes available in the rumen. As carbohydrate availability increases, more dietary protein can be incorporated into the rumen microbes as microbial protein.
The rate of protein digestion in the rumen is fairly well described using SIP as the rapidly available protein and the remainder of the DIP as the slowly available protein. There is no universally accepted system for describing the rate of non-fiber carbohydrate digestion. If the principle starch source is cornmeal, a good rule of thumb is to have 20-30% of the NFC composed of rapidly available carbohydrates such as sugars, bakery product, and flour. If barley, steam-flaked corn or high moisture corn is used, amounts should be limited so that these sources provide no more than 60% of the NFC in the ration.
Utilization of Protein and Carbohydrate by Rumen Bacteria
(Adapted from Nocek and Russell, 1988)
Simple sugars contain one or two units of sugar (such as glucose) and they are rapidly fermented in the rumen (300% per hour) to the stronger acids, propionic acid and lactic acid. Sucrose is a common sugar that is made up of a unit of glucose and a unit of fructose. Sucrose is the main sugar in the sap of plants and is found in forages, citrus pulp, beet pulp and molasses. Other sugars commonly fed to cows include lactose (milk sugar) and dextrose.
Sugars have generally been used to improve palatability of feeds but it has been found that the rumen microbes will actually respond to the addition of sugars in the diet by producing more microbial protein. More microbial protein production means more milk production. Sugars help to provide the rumen microbes with the energy that they need at the right time in relation to other carbohydrates in the ration. Sugars can help the rumen microbes to capture and use more of the nitrogen in the diet, especially nitrogen coming from rapidly digestible sources such as, urea and the soluble protein in ensiled forages. The amount of response generated from sugar supplementation will depend in part on the blend of starches in the ration. If most of the starch is slowly fermentable, such as cornmeal, sugar will be needed more. If there is already a blend of starches, some fast fermenting (like high-moisture corn and barley) and some slow fermenting, the rumen microbes will respond less to the addition of sugar. Too much sugar will result in a spike of acid in the rumen and rumen acidosis.
The sugar content of many dairy cow rations that are not supplemented with sugars, is only 1.5-3% of the dry matter. But, as a general recommendation, 4-6% of the diet dry matter should be sugar. That would usually be equivalent to 2-4% supplemental sugars in high production rations.
Rumen acidosis occurs when the cow’s rumen pH drops below 5.8. When the rumen microbes ferment sugars and starches, they produce large amounts of volatile fatty acids (VFA’s) (especially propionate and lactate). Rumen acids are buffered by saliva generated when the cow chews. Acid levels are controlled to a lesser but still significant extent by added buffers like sodium bicarbonate. VFA’s are absorbed from the rumen via rumen papillae. If the total acidity in the rumen builds, rumen pH drops. The rumen bacteria do not grow well when the rumen is acidic. Those bacteria that ferment fiber are especially affected. Dry matter intake declines, fiber digestibility is reduced, rumen microbial protein production is limited, and milk production suffers. What people fail to realize is that if sub-clinical rumen acidosis occurs for several hours each day, it may cause an apparently healthy cow to produce 120 pounds (55 kg) per day instead of 125 pounds (57 kg) per day.
Avoiding Clinical and Sub-clinical Rumen Acidosis:
Control Non-Fiber Carbohydrates (NFC) -- Avoid sudden increases in NFC (use a prefresh diet and gradually increase grain after calving). Don’t exceed 40% NFC in rations. If the principle starch source is cornmeal, a good rule of thumb is to have 20-30% of the NFC composed of rapidly available carbohydrates such as sugars, bakery product, and flour. More than 20-30% of the NFC from these rapidly digestible carbohydrates will induce more acidosis. If barley, high moisture corn, or steam-flaked corn are used, they should provide no more than 60% of the NFC in the ration. Avoid slug-feeding grain (no more than 10 pounds (4.5 kg) fed at one time).
Meet Fiber Needs -- Fiber counteracts the acid produced from the digestion of NFC by its own intrinsic buffering capacity as well as by stimulating saliva production to buffer the rumen. Long fiber stimulates the movement of rumen contents to increase the absorption of acid out of the rumen. 15% of the particles in the diet should exceed 1.5 inches in length. Roughage NDF should make up more than 21% of the diet. Roughage should be fed prior to grain or in a TMR. Forage or TMR should be available 24 hours/day. Consider adding two pounds of hay greater than 3 inches or 8 cm in length to your TMR. Observe bunks closely for sorting.
Add Buffer, such as sodium bicarbonate, to the ration. Offer buffer and salt free-choice.
Limit Heat Stress. Cows that are heat stressed will eat less forage. Use fans and misters. Open up the barn.
Beta-glucans and galactans are present in small amounts in some grains and beans fed to cows. Pectins are present in feeds like beet pulp, citrus pulp, soy hulls and alfalfa. Beta-glucans, galactans, and pectins, also referred to as soluble fiber, must be fermented in the rumen since enzymes in the intestine cannot break them down. Soluble fiber is fermented rapidly like NSC but yields the VFA acetic acid, which is weaker acid than propionate and lactate, as a by-product. Thus, soluble fiber generally does not dramatically lower rumen pH and cause acidosis.
Some laboratories distinguish between NFC (non-fiber carbohydrate) and NSC (nonstructural carbohydrate). They define NFC by the above equation [100-(%NDF + %CP + %Fat + Ash)]. They define NSC as only the starches and sugars in the feed or forage. Starches and sugars can be determined directly by enzymatic analysis. It is probable that in the future most nutritionists will distinguish and balance rations individually for sugars, starch, and soluble fiber, rather than grouping them all together. Each of these fractions is fermented differently, producing variable effects on production and health of the cow.
Comparative Analysis of Some Byproduct Feeds
Corn Gluten Feed
Distillers Dried Grain
Wheat Mill Run
NFC = (100 –(Ash+CP+Fat+NDF)), NSC = Enzymatic determination of sugars + starch
Source: DePeters, E.J. et al, 2000 as cited by Hinders, 2000.
In situations where acidosis is suspected, it may be desirable to increase the amount of soluble fiber in the ration and reduce the amount of starch and sugar. Often when poor quality (high fiber, low fiber digestibility) forages are used in rations designed for high production, starch and sugar levels become high, forage NDF has already been maximized, and more energy is still needed to support milk production. Soluble fiber can provide the added energy needed yet it will ferment to form the weaker acid, acetic acid, and not cause rumen acidosis.
Economic considerations and forage inventories sometimes dictate the use of commodities containing large amounts of soluble fiber and rapidly digestible NDF to substitute for forage fiber. These feeds contain a large amount of rapidly digestible NDF but marginal levels of effective fiber. As a result, total ration NFC levels are typically reduced (32-35% NFC).
Even though most of the dietary NFC is digested in the rumen, there can be a significant amount of starch digestion in the small intestine using the enzyme, amylase. Some researchers have suggested that the cow gets more energy from starch digested and absorbed as glucose from the intestine than she gets when it is broken down to VFA’s in the rumen. But, there appears to be an upper limit to the starch digesting capacity of the small intestine.
As cows achieve higher levels of intake and rate of passage of nutrients to the small intestine increases, the importance of intestinal starch digestion becomes more apparent. Based on one research review, 5-20% of consumed starch is digested after the rumen, mostly in the small intestine. In a study conducted at the University of Illinois, dairy cows digested more than 9 pounds (4 kg) of corn starch after the rumen.
Soluble fiber and starch can also be fermented in the cecum (hindgut) and large intestine. VFA’s are produced and absorbed from the cecum and large intestine but the microbial protein that is produced cannot be used. It passes out in the manure.
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Hinders, R. 2000. Common byproduct feedstuffs nutrient profiles confirmed in California study. Feedstuffs. September 11, 2000, p. 10.
Hoover, W.H. and T.K. Miller-Webster. 1998. Role of sugars and starch in ruminal fermentation. In: Proceedings of the Tri-State Dairy Nutrition Conference, Fort Wayne, IN, p 1.
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Nonstructural and Structural Carbohydrates in Dairy Cattle Rations
B. Harris, Jr., Ph.D., University of Florida
Mostly a review of literature with the main focus on structural (NDF) carbohydrates, rather than nonstructural (NFC) carbohydrates.
Protein and Carbohydrate Nutrition for High Producing Dairy Cows
Rick Grant, University of Nebraska - Lincoln
Very academic overview of the basics of protein and NFC nutrition. Many tables with general guidelines.
Feed Nutrients In: Feeding the Dairy Herd North Central Regional Extension Publication
J.G. Linn et al.