If cows could talk, it would be easy to figure out how good your hay is. Until then, we have to utilize a forage test to tell us if our hay is getting the job done that we think it is. Unless you are used to looking at forage reports, they can be hard to interpret. What follows is my version of a real simple explanation of the major terms on a forage report.
Key Forage Quality Terms, In Order of Importance
Total Digestible Nutrients (TDN) – This is the most important value on the report. I’ll bet you expected crude protein to be listed first. Actually, protein is seldom the limiting factor in ruminants, except for growing or lactating animals. TDN is a calculated estimate of the digestibility or energy content of forage. TDN goes down as forages become more mature. Energy is the most limiting nutrient in most if not all forage based livestock diets.
Acid Detergent Fiber (ADF) – This is the relatively indigestible fiber in a forage sample, containing cellulose, lignin and silica. ADF values rise as forages become more mature. ADF and TDN move in opposite directions. The higher the ADF, the lower the TDN.
Neutral Detergent Fiber (NDF) – This is the total fiber in a forage sample, made up of cellulose, hemicellulose, lignin, and ash. It is used to estimate intake. Like ADF, NDF values rise with forage maturity. Low NDF values indicate livestock can consume more forage.
Relative Feed Value (RFV) – This is an index for ranking cool-season grass and legume forages based on combining digestibility and intake potential. It is calculated from ADF and NDF. The higher the RFV, the better the quality. The RFV of full bloom alfalfa is about 100. RFV is only valid for ranking similar type forages, such as comparing one grass hay to another.
Crude Protein (CP) – This is an estimate of protein in a forage, calculated by multiplying % nitrogen by 6.25. By now, you are probably exasperated at my listing crude protein at the bottom of this list. I do so to make a point – we have to look further than protein to know if your forage is ‘good.’
Remember that the ultimate measure of forage quality is the performance of the animals to which it is fed. Since cows still can’t talk, you will need to observe how much they eat and how well they maintain body condition to ‘listen’ to what they are telling you about your hay. Happy foraging. ~ Jimmy Henning, from Farmer’s Pride