Forage analysis reports from a commercial feed testing laboratory often can contain more than 70 potential lab analyses. All those numbers have value in specific situations, but rarely, if ever, would one want or need all 70 results for a single sample. Some of the numbers are needed mainly for routine ration formulation (e.g., mineral concentrations), and some of the measurements might be needed to help solve specific problems (e.g., mycotoxin concentrations).
A core set of analyses should be conducted routinely on all forage samples. This core set of information is needed for ration formulation and can be used to evaluate the overall quality of the forage, estimate an actual or relative economic value of the forage, and for inventory management (assigning different quality forages to different types of animals). Analyses beyond this core may be needed to fine-tune diets and adjust evaluation decisions under specific situations. As discussed in a previous article (Proper Use of Forage Composition Data for Formulating Diets for Dairy Cows), using an average of data from two or more samples is much better than using data from a single sample.
The core set of analyses (Table 1) are dry matter (DM), neutral detergent fiber (NDF), in vitro NDF digestibility (IVNDFD), net energy for lactation (NEL), crude protein (CP), and ash. Each analysis will be discussed below.
Dry Matter (DM)
The concentration of DM (or conversely moisture) in forage is the single most important number when making forage harvesting decisions because it determines whether hay or silage will store properly. Forages harvested too wet for hay or too wet or dry for silage or baleage are at a high risk for spoilage or overall low quality after storage. The DM concentration of stored forage is needed to adjust the as-fed amounts added to the diet. Hay and silage with DM concentrations outside the acceptable range should be discounted heavily when purchasing because of the high risk of spoilage. Forage with the improper DM concentration may not be an acceptable feed for any class of livestock (e.g., it may be moldy), or you may need to limit its use to lower production animals (e.g., bred heifers).
Neutral Detergent Fiber (NDF)
The NDF concentration is related to the economic value of forages because forage NDF is considered an essential nutrient (needed to maintain rumen and cow health). Therefore, higher NDF concentrations could enhance the value of a forage; however, increased concentrations of forage NDF can lower intake and milk yield, which would reduce the value of a forage. Almost always, the economic costs of high NDF concentrations outweigh the costs of low NDF concentrations. The NDF concentrations in haycrop forages (grasses, legumes, and mixtures) have a much stronger correlation to intake and milk yield than does the NDF concentration of corn silage. This is because the NDF concentration in haycrop forages is positively correlated with plant maturity (i.e., as plant maturity increases, NDF concentrations usually increase). As maturity advances, digestibility of DM and NDF tends to decrease. As a corn plant matures, the grain component increases and this dilutes NDF so that NDF concentration in corn plants often has a negative correlation with plant maturity and with fiber digestibility. The NDF concentration has less value in estimating quality of corn silage than for other types of forage.