Ask a cattle producer why he feeds a liquid supplement and he'll say convenience, reduced labor, and lower cost. Liquid-feed supplements have been used in many situations with many different outcomes, some good, some bad. Hundreds of research trials evaluating liquid supplements and comparing them with other feeds have yielded inconclusive results, but even so, producers annually feed over a million tons of the supplements to animals on forage-based diets, and the tonnage increases each year.
At least part of the reason for inconsistency and unpredictability of liquid feeds has to do with their traditional ingredients and their digestibility. They are most commonly fed to beef cows as a winter protein supplement. Molasses is generally the base, but since it is low in protein, it must be fortified with a protein source that will dissolve or suspend evenly in it. The most common product used has been urea, a nonprotein nitrogen (NPN) source. Its bitterness can limit consumption of the supplement.
Regardless of diet, microorganisms (bugs) in the rumen break down feedstuff, releasing nutrients. The bugs use some of these nutrients, and some are directly available to the animal. They convert much of the protein and virtually all the NPN into ammonia, which they then use to reproduce. The microorganisms must also have a source of energy to carry on this process. In an ideal environment, they have adequate energy to efficiently use all the ammonia present. Urea, which most liquid feeds contain, is degraded to ammonia very quickly in the rumen. If the energy level in the diet is high, such as in a feedlot ration, the bugs use NPN efficiently. On low-energy diets or diets from which energy is released more slowly, like dry grass or low-quality hay, NPN conversion can be very inefficient, resulting in a buildup of ammonia. This unused ammonia is absorbed through the rumen wall into the bloodstream and eventually excreted or recycled through the saliva. In extreme situations, toxicity can occur.
Note: Much of the protein that escapes degradation in the rumen and that is in the bugs that die is absorbed farther down the digestive tract and is an important source of protein for cattle.
Quantity and quality of energy and protein in the diet are the primary determinants of how healthy the bug population is and how efficiently it works. The dynamics of the interactions of the NPN, microorganisms, forage quantity and quality, weather, animal, and desired performance, among other things, determines the success of feeding molasses-urea liquid supplements. And much is still unknown. It seems these traditional liquid supplements fit well for maintaining mature cows when there is plenty of forage that is at least 48 percent total digestible nutrients and less than 8 percent crude protein (Herd, Dennis B., College Station, Tex.: Research on Molasses Supplements-Liquid and Dry. Beef Cattle Short Course, Texas Agricultural Extension Service, August 9-11). They also work well when supplemental crude protein needs are less than 1 to 2 pounds per day, as with dry, pregnant cows.
Recently, liquid-feed manufacturers and cattle producers have added other ingredients to molasses-based feeds, which has resulted in a wide array of products with equally broad nutrient analyses. In many situations, these products have improved cattle performance. Fats can increase the energy value of liquid supplements. Natural protein sources that largely bypass degradation in the rumen and are absorbed later can help eliminate inconsistency in some situations. Vitamins, minerals, and antibiotics have also been added to some products.
For many producers, liquid-feed supplements have been and will continue to be a feasible alternative to dry supplements. As with any supplemental feeding program, success depends on knowing the nutritional requirements of the cattle, the quality of the forage, and the nutrient deficiencies that need to be corrected by the supplement; then the producer can select and deliver the right product.
Our Agricultural Testing Services lab can analyze your forage or hay. We can also help you evaluate your supplemental feeding program and options. Ryan Reuter has written a program to compare the total costs of whatever supplements you might consider. It is available on our Web site.