Reading a forage report
Everyone has their own way of reading a forage lab report and focusing on the information they feel is most important to them. As a forage specialist, I focus on the following items in this order.
1. What is the feed?
This is the first thing that I look at in a lab report because it frames how I look at the report. Alfalfa appears differently than corn silage. For example, I expect corn silage crude protein content to be roughly 9%. If that was the crude protein content of alfalfa, I would be worried!
2. What is the dry matter (DM)?
The moisture (or DM) content of the silage is probably the biggest variable impacting silage quality. Wet silages are prone to seepage and wasteful fermentations. Dry silages have more pores throughout the silage mass, which can mean more oxygen pockets and more spoilage. Dry corn silage typically has lower digestibility, but higher starch content because it is reflective of a more mature plant. Drier silages also undergo a stunted fermentation, which can result in less overall acids. In general, the ideal DM for corn is 32% to 35% and the ideal DM for alfalfa is 40% to 45%.
3. If it is fermented, how well did it ferment? I look at pH as a general indicator of this. The lower the pH, the better. A low pH (higher acidity) will inhibit the growth of undesirable microorganisms, such as clostridia and enterobacteria. A low pH will also reduce protein degradation and minimize ammonia. A pH higher than normal means the silage did not ferment well or it is unstable/spoiled. A normal pH for corn silage is 3.7 to 4.2 and a normal pH for alfalfa silage is 4.2 to 4.5. As a rule, we expect the pH of alfalfa to be higher than corn silage because of the buffering capacity of the crop. In other words, a pH of 4.3 on corn silage is bad, but this is great for alfalfa.
4. What shape are the proteins in? Not only do I look at the total quantity of protein, but I also look at ammonia and soluble protein as markers of “protein health.” Ammonia is the result of degradation of the amino acids in plant proteins. The two main times that ammonia forms are during the initial fermentation and during storage. Ammonia formation during the upfront fermentation is undesirable as it generally reflects DM losses, protein wasting, and an overall slow and undesirable fermentation (such as a clostridial or butyric fermentation). During storage, ammonia levels of alfalfa, in general, do not increase, but ammonia and soluble protein levels of corn silage do increase during storage due to degradation of the prolamin protein matrix that surrounds starch within the corn granule. Thus, in corn, increased ammonia levels and soluble protein levels reflect increases in starch digestibility. In alfalfa, typical ammonia content should be below 12%, but ammonia levels can be more variable in corn silage.
5. What is the starch content? Starch values range from 15% to 45% in corn silage and 65% to 70% in corn grain. Starch content of alfalfa is always low and doesn’t necessarily need to be a concern (it usually isn’t reported on alfalfa reports), but a good rule of thumb is to aim for at least 30% starch in corn silage. If the starch content is low in corn silage, it is probably because the corn is immature. Look at the DM to confirm this. The longer the corn silage and high moisture corn is ensiled, the higher the ammonia-N, soluble protein, in vitro starch-D, and starch kd will be. Highly digestible starch is good because it means you’re getting most of the corn kernels, but exercise caution to avoid acidosis with very highly degradable starch.
6. What is the fiber content? Fiber is one of the most important parts of a forage. High-quality fiber will drive production and rumen health, and the variables I look at to measure this are:
- aNDFom: How much fiber is there?
- 30-h or 48-h NDF-D: How digestible is the fiber in 30 or 48 hours?
- NDF kd rate: How quickly is the digestible fiber consumed by the rumen microbes?
- uNDF240: How much of the fiber is not digestible EVER in the rumen?
Technology is makes leaps and bounds so quickly, and laboratory procedures are no exception. However, with all these advances come many new terms on a laboratory’s nutrient analysis report. Talk to your local Vita Plus consultant if you would like help in diving deeper into a lab report.
About the author: Dr. Michelle Chang-Der Bedrosian is a Vita Plus forage products and dairy technical service specialist. Chang-Der Bedrosian earned her bachelor’s and master’s degrees in animal science at the University of Delaware. She continued there to earn her Ph.D. in animal and food science, specializing in forage research with Dr. Limin Kung. Her thesis research centered on the use of a protease to improve starch digestibility earlier in the ensiling process. A New Jersey native, Chang-Der Bedrosian gained much of her farm experience during her collegiate years, milking cows, working in a forage laboratory, and performing dairy research. Based in Madison, Wisconsin, Chang-Der Bedrosian’s responsibilities at Vita Plus include forage product research and development, dairy research, and dairy technical services.
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