Forage quality is determined by nutrient concentration, nutrient digestibility, and dry matter intake of the forage.  Laboratory analyses to quantify forage chemical composition enables nutrient concentration and digestibility to be estimated. Energy content of forages generally estimated using a mathematical equation that relates a fiber fraction to an energy value, such as TDN. Forage analysis should be used to minimize production costs by providing a balanced diet that allows optimum animal health and performance. Different feedstuffs testing methods are available to determine quality of feedstuffs utilized in a ration. 

Near infrared reflectance (NIR) gives a fast accurate evaluation of the individual feedstuffs in a cost effective manner. This test is typically used to evaluate the macro-ingredient level of a common feedstuff. NIR is the method most commonly used to analyze forage nutrient levels.

Wet chemical analysis requires more time for nutrient analysis and is typically more accurate in the evaluation of a feedstuff or total ration, and analysis cost is higher. Wet chemistry is the preferred method for micro-ingredient determination or when a more accurate evaluation of nutrient level is desired.

Forage and Feedstuffs Analysis

Forage and feedstuffs analysis is a critical component in developing a Year-Round Range Program because forages and feedstuffs consumed by cattle are the foundation of the Year-Round Range program. Therefore, one must know the actual nutrient content of available forages and feedstuffs. “Book values” of forages and feedstuffs are a good starting point and are often utilized in developing feeding programs.  However, book values and can be misleading because they are based on averages. Forage and feedstuff nutrient values can vary greatly based on:

• Soil type the forage and feedstuff are raised on

• Soil fertilization

• Weather conditions – wet versus dry

• Time of year harvested

• Stage of maturity at harvested

• Storage conditions after harvest

A grass hay or feedstuff sample from the same field can vary greatly from one year to the next. Forage quality also changes throughout the year. Figure 8 illustrates the change in dry matter digestibility of Western Wheatgrass over a five-year period.

Figure 8  Seasonal Changes in the in vitro Dry Matter Digestibility of Western Wheatgrass on the Grazing Intensity Trial (1995 to 2000)

    

Reference lines indicate the total digestible nutrient (TDN) requirement of a 1,000 lb lactating cow of average milking ability (56.6%) and a 1,000 lb dry cow in the middle third of pregnancy (48.8%) (NRC, 1984).
Source: B. Patton, J. Canton, and P. Nyren, North Dakota State University

Development of a cost-effective supplementation program can best be accomplished when actual forage and feedstuff nutrient content has been determined.

Forage Intake

Forage consumption is affected by many factors:

• Quality of forage available – As quality of the forage base decreases, intake also decreases

•  Quantity of forage available

• Protein content of the diet – If protein is inadequate to meet microbial requirements, forage intake will decline

• Environment

An accurate estimate of forage intake and how supplementation will affect intake is required to effectively manage a cow’s nutritional program. Table 4 provides estimates of the daily dry matter intake for dry and lactating cows under three supplementation programs (none, protein, or energy). Protein supplementation (digestible intake protein or DIP) will increase the intake of digestible dry matter of low- and medium-quality forages. Protein supplementation of forages with greater than 9% crude protein will have little effect on organic matter digestibility and intake. Researchers at the University of Nebraska observed that 0.3 lb per head per day of supplemental DIP maximized forage utilization and performance of cows consuming low-quality dormant winter range.  When designing supplementation programs for low-quality forages, two factors must be considered:

• Forage availability – Is the forage base adequate to meet animal energy requirements? If not, stored forages and other products must be considered to meet energy needs.
   

•  Limiting nutrient – The first limiting nutrient in low-quality forages is digestible intake protein. Starch (grain) supplementation over 0.3% of body weight will reduce forage utilization and intake if degradable intake protein is not adequate.

Table 4 Estimated Intake of Forage With and Without Supplementation

	Forage Intake (% BW, DM Basis) of Brood Cows
	Dry, Bred Cow	Lactating Cow
Low-Quality Forage (<7% CP)
No supplement	1.5	2.0
Protein Supplement	1.8	2.2
Energy Supplement	1.5	2.0
Average-Quality Forage  (7-9% CP)
No supplement	2.0	2.3
Protein Supplement	2.2	2.5
Energy Supplement	2.0	2.3
High-Quality Forage (>9% CP)
No supplement	2.5	2.7
Protein Supplement	2.5	2.7
Energy Supplement	2.5	2.7

Source: C.A. Hibbard and T.A. Thrift, Oklahoma