Are you a label reader? Probably not, unless you get bored when you are on “business” in the bathroom and you don’t have Readers Digest or the local daily newspaper in arms’ reach.
But take a look at the labels on the bottles of hand or body lotion, sunscreen and skin moisturizer.
Very high on the list (and ingredients are listed in order from highest to lowest concentration), you will find glycerin (another name for “glycerol”). You also will find it in teat or udder ointment.
What it is
Glycerol is an odorless, colorless and sweet-tasting viscous liquid, even at low environmental temperatures. It is the backbone for fatty acids to form fat (or triglycerides).
Fat from soybeans, tallow, restaurant grease, etc. is presently being used for biodiesel production. The fatty acids are the integral part of the fuel, but the glycerol is a byproduct from the process.
Every gallon of biodiesel produced will general about 0.75 pounds of crude glycerol. So, with the increased availability of glycerol as a byproduct of biodiesel production, it is being investigated as a feed ingredient for dairy cattle.
The bacteria in the rumen (first stomach compartment) can use glycerol to primarily produce propionate and the propionate will be converted to glucose by the liver of the cow.
In a recent Purdue University study, 60 dairy cows were fed diets containing 0 percent, 5 percent, 10 percent or 15 percent glycerol (replaced corn).
The diets contained 31.9 percent corn silage, 10 percent alfalfa haylage, 12.2 percent alfalfa hay and 45.9 percent concentrate (including the glycerol).
The concentration of nonfiber carbohydrates across the diets was approximately 39 percent. Feed intake, milk yield, milk fat and milk protein were similar among the dietary treatments (53.5 pounds per day, 81.2 pounds per day, 3.6 percent and 2.85 percent, respectively).
Concentrations of milk urea nitrogen were lower with diets containing glycerol and cows consuming 10 percent or 15 percent glycerol gained more weight than cows not fed glycerol.
Ohio State study
We also recently completed a study at Ohio State University whereby 48 cows (averaged 112 days in milk) were fed different concentrations of glycerol and nonfiber carbohydrates: 0 percent glycerol and 37 percent nonfiber carbohydrates; 5 percent glycerol and 37 percent nonfiber carbohydrates; 10 percent glycerol and 37 percent nonfiber carbohydrates; or 10 percent glycerol and 42 percent nonfiber carbohydrates.
Diets contained 37.4 percent corn silage, 9.1 percent hay and 53.5 percent concentrate (including the glycerol).
Feed intake, milk yield, milk protein and milk urea nitrogen were similar among the dietary treatments (52.6 pounds per day, 87.1 pounds per day, 3.06 percent, and 14.3 milligrams per deciliter).
Milk fat percentage was decreased with glycerol addition (3.52 percent, 3.18 percent, 3.19 percent and 2.93 percent, respectively), especially when 10 percent glycerol was fed with 42 percent nonfiber carbohydrates.
In each of these studies, cows were fed the diets for eight weeks, and based on the results from these two studies, as well as some other published research, we can conclude that glycerol has value as a feed ingredient for dairy cattle.
Feeding glycerol may have to be limited more when diets are rather high in nonfiber carbohydrates. The effect observed in milk fat percentage in the OSU study may not be a negative effect on the ruminal fermentation because feed intake was not altered.
Therefore, the effect may be on fat synthesis in the mammary gland.
Feeding glycerol at 5 percent to 10 percent of the dietary dry matter should be valuable nutritionally and should pose limited risks to animals.
Given the viscous nature of the product, it may help reduce sorting of total-mixed rations by dairy cows.
However, there is caution with the findings of these two studies. Both projects were conducted using food-grade glycerol.
Crude glycerol from biodiesel production will contain unused catalyst (e.g. sodium hydroxide or potassium hydroxide), methanol and salts. The actual amount of glycerol in crude glycerin may range from 75 percent to 90 percent.
The Food and Drug Administration has issued a letter stating that if methanol is over 150 part per million (0.015 percent), it should not be used for animal feed.
So, additional research is needed to determine the variation in composition of crude glycerol, including the concentration of contaminates that are of particular risk to animal health.
Once these are better identified, more defined feeding guidelines for crude glycerol can be established based on not only the nutritional value of the ingredient, but also the limitations due to the impurities that may cause some risks.
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do you have some scientific articles about glycerol
There are been several papers published on feeding glycerol; one of the more recent ones with respect to feeding it to dairy cattle is by Dr. Shawn Donkin at Purdue University: Journal of Dairy Science 92:5111-5119 (2009).