by Brian Freking, Oklahoma State University

Ruminant animals are naturally meant to consume a diet based on forage or roughage. Pasture and hay should usually make up most of the diet. When purchasing hay, many people may utilize visual quality characteristics such as greenness, weed content, leaf-to-stem ratio, etc., but we should strive to know the nutrient content. Here are some tips for reading a forage analysis.

Sample report

The report in Fig. 1 has been run for a basic analysis, which provides protein and moisture, acid detergent fiber (ADF) and total digestible nutrients (TDN), as well as net energy for maintenance (NE_m), lactation (NE_l) and gain (NE_g). Once moisture content is determined, we want to focus on the Dry Basis column for accurate nutrient comparisons.

Moisture percentage: The prime moisture content for hay will range from 10% to 20%, with the ideal being approximately 15%. Moisture above 20% can lead to risk of mold formation and potential for spontaneous combustion.

Crude protein (CP) is what most people look at when evaluating a feed ingredient. Total nitrogen is the fraction of the plant including true protein and non-protein nitrogen. CP in forages is simply calculated by multiplying total nitrogen by 6.25.

ADF, %, is a sub-fraction of neutral detergent fiber (NDF, %) which was not evaluated on this report. NDF is the whole fibrous fraction (cellulose, hemicellulose and lignin) plus small amounts of silica and minerals that constitute most of the plant cell wall. ADF is composed of cellulose, lignin and a minor amount of silica and minerals. Both ADF and NDF give us an idea of fiber content. The more mature the plant becomes, the higher the amount of fiber it will contain. We refer to these values as being negatively correlated. The higher the ADF value, the less digestible the forage will be. The NDF value is negatively correlated with forage intake, so the higher the number, the more likely intake will be reduced.

TDN is a simple measure of energy consumption expressed as a fraction. It is calculated from ADF. TDN tends to overestimate the energy value of roughages compared to concentrates (grains). It still is a good measure of performance predictability based on its value.

The California Net Energy System provides improved predictability of the productive response of animals, depending on whether feed energy is being used for maintenance (NE_m), growth (NE_g) or lactation (NE_l). Since this system is more complicated, most people rely more on the TDN value.

In summary, high-quality forage is the end product of good growing conditions, correct harvest timing and proper handling and storage from harvesting to utilization. Knowing the nutrient content of forages goes a long way in managing the performance of livestock.