Lots of data and producer experience support the importance of protein supplementation with low quality forages or winter grazing. An overriding issue is that protein supplements are often expensive and should be avoided if they are not needed. If they are needed, then it is wise to shop around for the best value for the dollar spent.
Base Forage Quality
First, be sure that the base forage is truly low quality that requires a protein supplement. The general rule of thumb is that low-quality forage is defined as containing 7% crude protein or less. This is based on 7% being the minimum protein content needed to support a viable population of rumen microbes. Once crude protein falls below that level, the rumen microbial population will not be large enough to digest the fiber in the diet. The second requirement to meet is that of the animal. In the case of a beef cow in mid-gestation at this time of year, the protein requirement is also about 7% of the diet. Once she enters the last trimester of gestation, that requirement will increase to about 8% of her diet.
Forage Analysis: It becomes very important to have forage analysis done on feedstuffs to determine whether they are deficient in protein or not. The cost of a feed analysis of about $50 may save thousands of dollars being unnecessarily spent on an unneeded supplement. Sampling hay is relatively straight-forward. Use a core sample on several bales from throughout the stack. Sampling a pasture is a little more complicated because grazing livestock are selective. It is best to pluck higher-quality portions of plants that animals are likely to select rather than harvesting entire plants to ground level.
Forage Protein Supplements
Any feedstuff that contains high enough concentration of protein to overcome the deficiency in low-quality forages can serve as a protein supplement.
Alfalfa Benefits: Alfalfa hay makes an ideal protein supplement. The protein in alfalfa hay is highly digestible and available in the rumen to feed the rumen microbes. Because of this, it stimulates digestion of the fiber in both the alfalfa and the low-quality forage. This stimulation of digestion also increases intake of the low-quality forage, and as result improves the total digested nutrients that the cow (or any other ruminant) receives. Research conducted at Kansas State University in the early 1990s demonstrated that good quality alfalfa hay was equally effective compared to a traditional protein cake based on soybean meal and milo grain. Not only did it provide a similar stimulus in digestion and intake of the low-quality forage, but also similar cow weight and body condition score through the winter, and it actually yielded a slightly higher pregnancy rate the next fall (88 and 96% for cake and alfalfa hay, respectively). Additional research at Oregon State University indicated that the quality of the alfalfa hay is relatively unimportant, as long as more alfalfa is fed when its quality is lower so that the same amount of protein is supplied.
Please bear in mind this not suggesting a diet consisting of only alfalfa hay. Using alfalfa as a supplement means that a few pounds are fed (just enough to overcome the protein deficiency), and the cow is expected to fill the rest of her daily intake needs with the low quality forage.
Finally, is alfalfa hay the best value for the dollar spent? The answer boils down to the delivered cost per ton of protein. For example, we can assume the purchase options are either alfalfa hay with 18% crude protein at $90 per ton, or a 20% protein cake at $180 per ton. The cost per ton of protein is $562 for alfalfa and $1059 for the cake. These calculations are made on a dry matter basis assuming the dry matter content for alfalfa hay is 89% and cake is 85%. The best value as a protein supplement is provided by the alfalfa. Be sure that the prices used here include the cost of delivery, both from the source to your place and the cost of feeding it to the cows. Delivery to the cows may vary depending on the equipment needed for each (i.e. tractor vs. pickup, bale feeders vs. bunks, etc.). The nice thing about using hay as a supplement is that most producers are already equipped to handle it.
If you produced the alfalfa hay, then it can be priced at the cost of production, which will usually be favorable compared to the cost of purchased feedstuffs. In addition, it provides an opportunity to add value to both the alfalfa hay and the low quality forage relative to purchased feedstuffs.
Using alfalfa hay, especially home-grown hay, provides an opportunity to meet protein deficiencies at a relative bargain.