Forage analysis valuable in developing winter feeding program

Determining the nutrient content of forages and other feeds through laboratory analysis is the best way to design a nutrition program that meets livestock requirements

A hay sample being emptied into a bucket.

Laboratory analysis to determine the quality of feedstuffs was developed more than 150 years ago.

“Since that time, the ability to accurately analyze forages has greatly improved, as has the ability to use results to improve livestock feed efficiency and performance,” says Janna Block, extension livestock systems specialist at NDSU’s Hettinger Research Extension Center.

“However, this valuable management tool is still underutilized by many livestock producers,” she adds. “Feed costs are by far the largest annual operating cost for most operations. Determination of nutrient content of forages and other feeds through laboratory analysis is the best way to design a nutrition program that meets livestock requirements in a cost-effective and efficient manner.”

The first step in analyzing forages is getting a representative sample. Hay samples should be grouped based on species (alfalfa, grass, etc.), field and harvest date. A “lot” of forage is defined as forage taken from the same field within a 48-hour period.

Inventory the number of bales in each lot and estimate needs for the winter feeding period, considering that the average dry matter hay intake is 2.5 per cent of cow body weight. Voluntary intake will increase with decreasing temperatures. In colder environments, producers may need to calculate forage needs based on 3.5 per cent to four per cent of cow body weight. Other factors that influence intake include cow size, body condition and forage quality.

In some cases, extremely low-quality forage will limit intake due to reductions in digestibility and passage rate. Determining nutrient concentration through laboratory analysis is the best way to avoid this type of issue and ensure that nutrient needs of livestock are met in the most efficient and effective manner possible.

When sampling hay, collect random samples from 10 per cent of bales (or no less than 20 samples) in each lot using a hay probe. A large number of commercially available hay probes are available for $100 to $150. Select a probe that can attach to a cordless drill and is 3/8- to 3/4-inch in diameter and 18 to 24 inches long.

Make sure the tip is sharp so that it cuts cleanly through a cross-section of hay.

The probe should be inserted at a right angle to the outside circumference of the bale for round bales and into the center of the ends of square bales. Mix the samples thoroughly in a bucket, place about one quart in a plastic bag and ship it immediately to a laboratory for analysis.

Analytical packages and prices will vary from one lab to another. Feed samples are analyzed using wet chemistry or near-infrared reflectance spectroscopy (NIRS). Wet chemistry utilizes heat and chemicals to break down and isolate nutrients in the sample. It requires a skilled technician and is usually more costly but also more accurate.

With NIRS analysis, nutrient values are characterized by infrared light reflectance in a spectrophotometer. Values for different types of feed are determined by comparing light wavelengths from samples of known nutrient values that were established by wet chemistry procedures.

The accuracy of NIRS is dependent on the calibration methods and feed library available at each lab. It is most useful for pure forage samples such as alfalfa or a single grass species.

Wet chemistry is recommended for mixed-grass forages, grains and coproducts. Wet chemistry also should be used when determining mineral content of feeds.

In general, dry matter (DM), total digestible nutrients (TDN; estimate of energy) and crude protein (CP) are used as the basis to determine forage quality and develop rations for livestock at various stages of production.

However, evaluating other components of the forage as well can be worthwhile. Mineral content can vary widely from year to year, so forage analysis is helpful in determining what the forages supply and what type of mineral supplement is needed. Of course, if the forage has any potential for nitrates or other contaminants, those should be tested for as well.

Forage analysis results can be combined with an estimate of animal nutrient requirements based on the stage of production. In general, dry, mature beef cows in midgestation require a minimum of 50 per cent TDN and seven per cent CP. In late gestation, minimum requirements increase to around 55 per cent TDN and eight to nine per cent CP. After calving and during early lactation, requirements are further increased to 60 per cent TDN and 11 per cent CP. If producers intend to increase the condition of gestating or lactating cows, higher quality forage and/or supplements will be necessary.

These general rules of thumb can be used to evaluate the best use of different forages based on the stage of production (feeding the lowest quality hay early and saving the higher quality forage for lactation). Remember that factors such as breed, cow body condition, milk production, age and environment will influence requirements. Computerized ration balancing is typically a necessary step in determining specific needs for an individual group of animals.

“Hay inventory combined with forage analysis will help determine availability and quality of the forage base and whether or not supplementation will be necessary to meet livestock requirements,” Block says.

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