Market Watch: Wholly Cow!
The addition of sugar to dairy rations has been primarily as a palatability enhancer and, if added as a liquid, to help prevent sorting.
Today, more and more rations are containing sugar as a nutrient ingredient to enhance rumen fermentation and boost milk and/or milk component production. Human nutritionists consider sugar a quick energy source and now dairy nutritionists are feeding sugars as a “quick energy” source for rumen microbes.
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Simple sugars like sucrose and lactose ferment very rapidly in the rumen (200 - 500%/hour) while complex soluble fiber “sugars” like pectin digest much slower.
As we learn more about rumen fermentation and the benefits of feeding “sugar” to dairy cows, there is a need to differentiate between various sources and types of sugar.
Sugar can generally be classified into two categories – simple and complex. The simple sugars are one or two sugar molecules. Glucose, fructose and galactose are single sugars and lactose (glucose-galactose) and sucrose (glucose-fructose) are double sugars, two sugar molecules connected together.
The two most common sugar sources supplemented into dairy rations contain single and double sugars. Whey contains lactose and molasses contains sucrose, glucose and fructose.
Complex sugars (multiple 5 and 6 carbon simple sugars connected together) make up the soluble fiber (pectin, fructans and hemicellulose) in forages and feeds. Common sources of complex sugars are beet pulp, citrus pulp, soyhulls and other high fiber byproduct feeds. These complex sugar, soluble fiber feeds are often used to replace some starch in diets.
The nonfiber carbohydrate (NFC), a calculated value, estimates the total combined starch and sugar content of a feed. It provides no information as to the individual amount of starch, simple sugar or complex sugar in a feed.
So a few years ago, forage and feed testing laboratories added a “sugar” analysis to their forage and feed tests. Most laboratories are using an ethanol soluble (ESC) method to separate starch from sugars, but lost in the analysis are simple sugars.
Thus, an ESC sugar analysis value provides an estimate of complex sugars, but not all fast digesting simple sugars. To get a “total” sugar value that includes the rapidly fermented simple sugars like lactose, a water soluble (WSC) method is now being used by some laboratories and reported as WSC sugar on test reports.
The WSC analysis includes all rapidly fermentable sugar carbohydrates, but not pectins, and is now the preferred “sugar” analysis.
Small amounts of ESC sugar are found in almost all forage, grain and byproduct feeds with the typical dairy ration containing 3 to 4% ESC sugar (DM basis). The sugar supplemented into rations is generally the simple and rapidly fermented sugars.
The concern with adding this type of sugar to the ration is that rapid rumen fermentation generally lowers pH and often results in acidosis. However, recent research from Canada (J. Dairy Science 98:2627) shows addition of 6% lactose to rations as a replacement for starch did not lower rumen pH.
The fermentability of the lactose increased butyric acid in the rumen that in turn stimulated growth of rumen papillae for increased volatile fatty acid absorption from the rumen.
Based on the Canadian study and other studies, replacing 3 to 5% of the starch in rations with WSC sugar (rapidly fermentable) can provide benefits in rumen function. With increased VFA absorption from the rumen, acids do not accumulate in the rumen depressing pH and become more available for milk and milk component production.
Transition cows and heat-stressed cows also may benefit from some readily fermentable sugar addition to the ration. The benefits of adding sugar to rations go beyond palatability enhancement.
