Alfalfa quality can be characterized in several ways, including color, leaf content, and chemical composition. Describing forage quality by chemical analysis is closely related to animal performance, giving a better indication of relative differences between forages. In addition, chemical analysis provides the least subjective and most uniform system for describing forage quality. Chemical analyses most commonly used as measures of forage quality are neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein (CP), and mineral concentration. Calculated variables such as digestible dry matter (DDM), dry matter intake (DMI), relative feed value (RFV), and net energy for lactation (NE_L, Mcal/lb.) also are useful measures used by hay marketers and nutritionists to describe forage quality and predict utilization.

NDF is a measure of cell wall or total fiber and increases with advancing forage maturity (see Table 5-2). As NDF increases, voluntary intake of forage by livestock decreases. Estimates of voluntary dry matter intake, as a percent of body weight, can be determined from NDF using the following equation.

The NDF concentration of alfalfa can be kept low by harvesting at an early stage of maturity and reducing leaf loss during harvesting.

Acid detergent fiber is the portion of the total fiber that is relatively indigestible and increases with advancing forage maturity. As ADF increases, DDM and energy content of forage declines. Estimates of digestibility and energy content can be determined from ADF using the following equations.

As with NDF, ADF concentration of alfalfa can be reduced by harvesting at an early stage of maturity and by reducing leaf loss during harvesting.

The RFV concept incorporates quality factors calculated from ADF and NDF into a useful index for comparing legume and legume-grass mixtures (see example below). The higher the RFV, the higher the quality and production potential of the forage.

For additional information concerning forage quality testing, refer to OSU Extension Fact Sheet F-2117.

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The nutrient requirements of livestock depend on numerous factors (e.g., age, body size, reproductive status, level of milk production, etc.). Because of this, certain qualities of alfalfa are best suited for specific classes of animals (Figure 5-2).

|       100 | 110 | 120 | 130 | 140 | 150 | 160   Relative Feed Value Figure 5-2.   Matching Relative Feed Value to Animal Needs.

Calves from 1-3 months of age benefit from eating high quality forage. Alfalfa provided to these animals should be greater than 18 percent crude protein and less than 42 percent NDF. Alfalfa for calves can be preserved either as hay or low-moisture silage (less than 55 percent moisture). High-moisture silage should be avoided because the high moisture content may limit intake and protein quality.

Feeding 3-12 month old heifers alfalfa that contains 16-18 percent CP and 42-46 percent NDF will generally provide optimal growth with minimum concentrate supplementation. Alfalfa containing 14-16 percent CP and 45-48 percent NDF will meet most of the nutritional needs of heifers 12-18 months old and lactating beef cows.

Heifers 18-24 months old and dry cows are able to utilize alfalfa of lower quality than other classes of livestock. Forage that is 12-14 percent CP and 48-52 percent NDF is adequate for these groups. However, because of its high calcium and potassium content, feeding large quantities of alfalfa hay to adult cows near the end of gestation may lead to metabolic problems at calving. For these animals, the amount of alfalfa offered should be limited to less than 12 pounds per head per day.

No other farm animal reflects differences in the quality of forage as does the lactating dairy cow. High producing dairy cattle need the highest quality forage, while dry beef cattle can use more mature forage with lower protein content and fiber digestibility. Lowering the quality of alfalfa fed to high-producing dairy cows can dramatically reduce milk production, especially in early lactation. Cows cannot physically consume enough digestible dry matter, even from high-quality alfalfa hay, to produce at maximum inherited capacity. Some level of concentrate (grain and protein supplement) is needed with any quality of forage offered to high-producing dairy cows to obtain maximum milk production. However, the higher the quality of forage consumed by the dairy cow, the lower the amount of concentrate needed to achieve higher levels of milk production and the less likely digestive upset or metabolic disorders will occur.

A good illustration of the importance of high-quality forage for milk production comes from a study conducted at the University of Wisconsin that compared alfalfa hay harvested at four stages of maturity fed to high-producing dairy cows (Table 5-1). Levels of concentrate fed were also varied to evaluate its effect on milk production at similar as well as different quality levels of alfalfa hay. In this study, the highest level of milk production was obtained on pre-bloom alfalfa hay at all levels of concentrate feeding. The highest output of milk and apparent peak in profitability occurred at the 54 percent level of concentrate feeding. The main point of this study is the impact forage quality has on milk production. It is also apparent that feeding higher levels of concentrate cannot substitute for lower forage quality. Cows fed pre-bloom alfalfa supplemented with 20 percent concentrate produced more milk than those fed full-bloom hay with 71 percent concentrate.

In general, high-producing dairy cows should be fed alfalfa hay with a quality analysis of at least 20 percent CP, less than 30 percent ADF, and less than 40 percent NDF (the "20-30-40" rule). Lactating cows, during the first 100 days after calving, have high and rapidly increasing nutrient requirements. Alfalfa containing 20-24 percent CP and 36-38 percent NDF is best suited for these animals. Alfalfa lower in CP and higher in NDF will require the feeding of additional amounts of concentrates to achieve a given level of milk production. Further, alfalfa with lower NDF concentrations may not provide enough fiber to maintain proper rumen function. Lactating cows during the last 200 days of lactation have reduced energy and protein demands as milk production declines. Therefore, lower quality forage can be fed after the first 100 days of lactation.

Can alfalfa quality be too high? If alfalfa is harvested too early, it will have low ADF content, high NDF digestibility, and high crude protein content. Although the energy content will be relatively high, it is still much lower than the energy content of corn grain. Diets containing very high-quality alfalfa with low NDF content must contain very high forage levels to meet the cow’s fiber requirement. This reduces the energy density of the diet because there is little room left for grain. Attempts to increase energy density by adding grain without regard to fiber requirements may result in metabolic disorders.

Furthermore, protein content of the diet will be excessive because of the high level of forage with a very high protein content. Excess protein is not only wasteful but also costs the cow energy to excrete, may reduce reproductive performance, and contaminates the environment. In addition, forage yields will be lower, and harvesting early may decrease the life span of the alfalfa stand. Rarely do livestock and dairy producers need alfalfa hay with greater than 200 RFV.

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The traditional response for many years to the question regarding when to cut alfalfa was, "Cut at 10 percent bloom for the best combination of yield, quality, and stand persistence." However, there is no single best cutting interval for alfalfa.

The best time to harvest will vary depending on projected use of the hay. If hay will be sold as high-quality forage (for dairy cattle), alfalfa should be cut at bud stage or earlier (23-day cycle or less). If alfalfa is being used as feed for a cow-calf operation where high quality is not as critical, it should be cut at 25-50 percent bloom (35-42 day cycle) to maximize yield and profitability. Figure 5-3 "Hay-making time lines" at the end of this chapter illustrates different harvesting cycle lengths.

Producers must decide what intervals are most appropriate for their operations and markets. For example, alfalfa cut when less mature (bud stage) may yield 20-30 percent less forage than mid-bloom hay (Figure 5-1); however, it will have much higher protein content and relative feed value than that cut at mid-bloom (Table 5-2).

If higher quality alfalfa can be sold for $15-$20 per ton more compared with lower quality forage, revenues may be greater with early cutting. If there is little or no price advantage for high quality, later cutting and fewer harvests per year will normally be more economical.

For growers who plan to consistently cut their alfalfa at bud stage compared with bloom stage, the following considerations are important. Assuming the first harvest is taken in late April or early May and that soil moisture is not limiting, a total of six harvests are possible on a 28-day cutting cycle. The last harvest would be taken mid-September (see Figure 5-3). This cutting schedule would compare with 4-5 harvests taken on a 35-42 day interval. Although annual yields may not differ greatly between the cutting schedules, added harvest costs of $22-$44 per acre would be incurred with the 28-30 day interval. A higher price must be obtained for the forage cut at bud stage to offset these costs.

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No clear advantage in animal performance has been demonstrated for alfalfa conserved either as hay or silage, although there is an indication that silage supports higher milk production and is more efficiently utilized by dairy cattle. Again, quality is the most important factor determining milk production potential from forage. Field losses are less when alfalfa is harvested at a higher moisture content; consequently, silage will have lower field losses than hay. Within each category (e.g., 13 vs. 18 percent moisture hay or 45 vs. 60 percent moisture silage) losses will be greater with higher moisture forage unless more expensive storage structures are used (oxygen-limiting vs. bunker silos).

The decision to harvest and store alfalfa as a high-moisture crop is primarily one of risk management. Most alfalfa produced in the western U.S. is baled because of good drying conditions and ease of transport. However, in the northern U.S., alfalfa typically has been ensiled because of the shorter drying time needed for silage versus hay, thus reducing the possibility of the crop being damaged by rain.

Dates shown in these haymaking time lines are assumed to be for central Oklahoma.  With normal growing conditions, producers in southern parts of the state should begin about five days earlier, and those in the north should delay first harvest about five days.  Temperatures during early April affect ideal timing of first harvest.  Dry periods during July and August frequently prolong harvest intervals during that period.  As an alternative, producers with livestock should consider utilizing late summer forage by grazing.  (See Chapter 7, "Grazing Alfalfa.")