Harvest Technique Affects Alfalfa Quality

FARGO - Jun 10/05 - SNS -- The quality of alfalfa produced can be affected by the way it is harvested, cautions a North Dakota State University dairy expert says.

"Quality affects price," says J.W. Schroeder, NDSU Extension Service dairy specialist. "For those aspects over which the alfalfa growers have control, unlike weather and insects, the rapid change in quality makes timing of the harvest paramount."

Recent hay auctions report mid-May, new-crop hay from Kansas and Nebraska was selling for $125 to $130 a ton, and round bales topping the market at $82.50 per ton on a load of second-crop hay from Iowa. One load of very wet new-crop, round-baled hay sold for $50 per ton.

"There begins the debate for sellers and buyer alike," Schroeder says. "What is the trade-off for yield and feeding value?"

Researchers in Idaho, Wisconsin and Pennsylvania jointly are investigating the trade-offs between yield and quality changes over multiple cuttings. Based on the data collected, alfalfa quality appears to change faster in the first cutting than in later cuttings. First-cutting alfalfa decreases about five points of relative feed value (RFV) per day. Second-cutting alfalfa decreases two to three points per day; and third and fourth cuttings decline one to two points per day.

This means that the earlier the stage of harvest, the higher the quality of the alfalfa hay that is available for feed or sale, according to Schroeder. Dairies want a minimum of 150 to 160 RFV, so because of the rapid decrease in value, producers should start to harvest when the RFV is 180 to 200. However, for dairy producers who raise their own hay, 150 to 160 RFV is ideal to promote dry-matter intake and maximize milk yield by keeping the diet forage-to-concentrate ratio at least 50-to-50, and preferably 60-to-40.

Relative feed value is an index that ranks cool-season legumes, such as alfalfa, and grasses by potential digestible dry-matter intake. It is calculated from digestible dry matter and dry-matter intake.

Digestible dry matter is an estimate of the feed's total digestibility and is calculated from percent of acid detergent fiber (ADF). Dry-matter intake is an estimate of the amount of feed an animal will consume in percent of body weight and is figured from percent of neutral detergent fiber (NDF).

The formula for determining RFV is:

Digestible dry matter (DDM) = 88.9 – (0.779 x percent of ADF)
Dry matter intake (DMI) = 120/(percent of NDF)
RFV = (DDM x DMI)/1.29

 For example, here's how to calculate RFV for hay or haylage
with 28% ADF and 35% NDF:

DDM: 88.9 – (0.779 x 28) = 67.1
DMI: 120/35 = 3.43
RFV: (67.1 x 3.43/1.29 = 178

RFV does not include the protein percent of the alfalfa, but it is an excellent measure of alfalfa quality because it reflects the crop's digestibility and intake potential, according to Schroeder.

"Obviously, the more mature the alfalfa at harvest, the higher the percent of ADF and NDF and lower the RFV," he says. "Rain-damaged hay also will be higher in ADF and NDF because the soluble sugars and carbohydrates can be leached out. Rain-damaged hay also is less palatable. Astute dairy farmers who purchase alfalfa not only utilize the chemical analysis and relative feed value, they also buy small quantities and feed some of it free choice to see if the cows readily consume it before purchasing larger quantities."

Dryland alfalfa growers in North Dakota often are not able to harvest more than two crops. But in states farther south, late-fall growth may change little in forage quality during mid- to late September and early October.

Research indicates that relative forage quality (RFQ), a newer measure of quality, changes about the same as RFV in the first cutting, but then declines about three points per day in the second, third and fourth cuttings.

The yield of standing alfalfa around harvest time varies considerably and increases up to 200 pounds per acre per day. Schroeder says that based on data from a number of studies, producers probably can plan on a yield increase of about 100 pounds per acre per day near harvest if growing conditions are average. This yield change is consistent across cuttings, except in late fall.

The daily yield increase will be lower in cool, cloudy weather, and if insects or diseases affect the crop, or drought occurs. It may be greater than 100 pounds per acre per day in periods of good moisture, sunshine and 75- to 85-degree weather.