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Testing Forages for Quality

27 October 2008

Testing Forages for Quality Can Save Dollars and Makes Cents When Designing Feeding Programs for the Herd, writes Dr. Rick Rasby, Professor of Animal Science Animal Science, University of Nebraska - Lincoln and published by Ohio State University Extension Beef Team.

As producers strive to reduce feed costs by investigating avenues to increase grazing days, many still have to use harvested forages in their year-round feeding program. Sampling and testing forages for quality can make designing a feeding program easy and economical. Nutrient concentration can vary considerably in feeds, especially forages. Protein in alfalfa hay can range from 10 to 25 percent of the dry matter and grass hay will contain between four and 18 percent protein. Beef cattle are most productive when fed or consuming a diet balanced according to their nutrient needs. When designing diets using harvested feeds, many rations are balanced using average values for each feedstuff and these "book values" often result in over- or under-feeding certain nutrients. More economical and better balanced rations can be formulated using nutrient concentrations determined from feed analysis.

From a forage standpoint, as plants mature, fiber concentration increases. Fiber is less digestible than other plant parts and fiber digestibility declines as plants mature. Both these factors cause the concentration of energy in plants to decline as maturity advances. In addition, as plants mature, the increase in fiber and bulkiness reduces the amount of the forage an animal can consume. For an example, cows don't quit eating straw because they don't like it, they quit because they can't stuff anymore into their rumen because of straw's low digestibility due to the high fiber content. Protein concentration also declines as plants mature. The three factors that impact forage quality are 1. maturity at harvest; 2. maturity at harvest; 3. maturity at harvest.

Getting a representative sample, packaging it properly for transport, knowing what to test for and understanding the number in the analysis are critical. These are the items that I plan to address. In the final segment of this article there will a discussion on nitrates in forages.

Sampling and Packaging: It is important that samples closely resemble the entire "lot" of forage. Each sample must represent only one "lot" of forage. A "lot" of forage consists of forage harvested from one field at the same cutting and maturity. All forage from the same "lot" should be similar for: type of plant(s), field (soil type), cutting date, maturity, and variety. Variation in any of these characteristics can cause substantial differences in the nutrient value of the forage.

Sample baled hay after curing (usually 17 to 21 days after baling), using a core sampler or probe. Such an instrument is essential for collecting a representative sample and most commercial labs will not accept a "grab sample" of hay. For large round and square bales, the probe should penetrate at least 18 inches into the bale and have an internal diameter of at least 3/8-inch. If the probe is 18 inches long or longer, 15 large round bales should be adequate if the "lot" size is 30 to 40 bales. Collect one sample from each bale by coring straight in from the center of the end of square bales and from the wrapped circumference of round bales. Place the entire sample into a plastic bag and seal tightly. For loose or compressed hay stacks, use a hay probe at least 24 inches long to collect 15 or more samples from each "lot". Sample loose hay stacks from the top and from the side. Compressed loaf stacks require six sampling locations: 1) top front, 2) top middle, 3) top rear, 4) lower front side, 5) lower middle side, and 6) lower rear side. For chopped or ground hay collect about 10 small samples during grinding process and place all the samples into one plastic bag and seal tightly. If you are sampling previously ground or chopped hay, collect about one-fourth of the samples from the top half of the pile and the rest from the lower half. Avoid allowing fines to sift between fingers.

Label the bag with your name, address, lot ID, and type of material. Most testing labs provide a description sheet to report this information and to request the desired tests. Place samples in polyethylene freezer bags, squeeze the air out of the bag, and seal tightly. If you are sending a sample of silage, double bag silage samples for extra protection. Use extra caution if subdividing a large hay sample because sub-sampling dry hay can result in loss of fines and leaves. Freeze samples containing over 15 percent moisture until shipping; store dry samples in a cool location.

Nitrates: High nitrates could be a problem for cattle producers planning to feed or graze annual forages such as corn, cane, grain sorghum, millet and Sudangrass. When plants are growing normally, they absorb nitrates from the soil, but stress factors, such as drought or hail, interrupt plant growth, reducing photosynthesis and conversion of nitrates to plant proteins. High nitrate levels in forages can cause nitrate toxicity in cattle, which can kill the animal or cause abortions in pregnant cows. Weeds such as pigweed, lambsquarter, ragweed and to a lesser extent, Russian thistle, have the potential to be high in nitrates. When reading a nitrate analysis report, producers should look at how the nitrate levels are expressed. The method used in expressing nitrates will determine what level is toxic to an animal.

With proper management, high nitrate forages can be fed safely. Dilute high nitrate feeds with safe (low nitrate) feeds. Also adapt cattle to diets that contain nitrates. Most losses from nitrates occur when hungry cattle are exposed to feeds that are high in nitrate. Some producers may feed drought stricken corn as "green chop". If you do this management practice, set the chopper head up to avoid the bottom 6 to 8 inches of the corn stalk. Most of the nitrates reside in the lower portion of the stalk. Assume that there are nitrates present, so adapt slowly. Chop only what will be fed in one feeding and do not let green chop sit in the wagon over night to feed the next day. Green chop that contains nitrates and sits overnight, the nitrate will be converted to nitrites and nitrites are more toxic to the animal than are nitrates.

October 2008

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