Importance of Forage Testing

MANAgEMENT

Importance of Forage Analysis; Making Sure Nutrient Requirements are Met

Heather Smith Thomas

Winter forages may need supplementation with protein or minerals. Jeremy Martin, PhD (ruminant nutritionist and reproduction manager, Great Plains Livestock Consulting) says it’s important to sample and test forages, especially after unusual weather patterns that may affect growing conditions.

“We always recommend testing, even on lower-quality cheaper ingredients of cattle diets. Cost of tests, relative to potential savings, is so small there’s no way to justify not doing it.” It can be costly if you oversupplement or under-supplement, so you need to know the nutrient values of your feeds.

“Ideally, you’d test forages or silages. Any small grains hay should be tested, because nitrates are potentially an issue with them,” says Martin.

Warren Rusche, SDSU Extension Beef Feedlot Management Associate, says weather conditions in some regions made it more difficult to put up hay or harvest crops.

“One of the things we’re concerned about is people relying on book values in terms of nutrient content. You need to know what the nutrient values of your specific feeds actually are,” he says.

Janna Block, North Dakota State University Livestock Systems Specialist, says hay samples after harvest, or before purchase, gives you a chance to evaluate hay and determine which group of cattle to feed which hay. “For protein, cattle need a bare minimum of 7% in the diet. Below that level, microbial efficiency in the rumen declines,” she says. There won’t be enough protein to “feed” the microbes that ferment and digest forage. Digestion slows and a cow can’t get adequate nutrients from what she’s eating, and also can’t eat enough to sustain herself, so she loses weight.

Forage that’s only 7% protein (and 50% TDN (total digestible nutrients)) might work for the mid-gestation dry cow, but is inadequate for cows in late gestation. “They need forages that are at least 55 to 58% TDN and 8 to 9% protein, to support fetal growth. This will also depend on condition of the cow. If you are trying to feed a thin cow to pick up in body condition she’ll need more nutrient-dense feed,” says Block.

“Cows in late gestation/ early lactation have the highest requirements—about 60% TDN and about 11% protein. This is a rule-of-thumb way to evaluate your forages and match them with various production groups. First-calf heifers have high requirements for growth as well as supporting a fetus,” she says.

It’s hard to create a ration for beef cattle without a forage analysis since nutrient values can vary so much, even within the same type of plants. Brome grass hay could be 6% protein or as high as 12% depending on stage of maturity and weather conditions while growing and during harvest.

“When feeding grass hay we need to know the protein level,” says Rusche. “If it’s 9 to 9.5% protein, we won’t need additional supplement, but if it’s only 7% that’s a different story. The rule of thumb I was taught is that cattle need something that’s at least 8%. If it’s below 8% and we supplement with protein we see improved digestibility and increased feed intake.”

Make sure cattle are eating enough, especially in cold weather. “If they don’t eat enough, and the forage is not very digestible, we’ve created an energy deficit in those pregnant cows, and set ourselves up for poorer calf health, poor colostrum quality, and poor rebreeding—so we didn’t save money by not purchasing protein,” says Rusche.

After calving, the cow needs even more protein for lactation. An investment in protein supplement when it’s needed will always pay off, but you don’t know if you need it unless you test your feeds.

Block recommends sampling each batch of hay, based on number of bales in each lot, and a lot consists of all the hay (same species) harvested off the same field under the same conditions (within a 48-hour period). “Some people might just sample what they think is their worst hay, to know what the bottom level is, but we can’t put together a nutrition program without a total feed analyses, to be able to target when you’d want to feed certain forages or might need a supplement,” she says.

“Any feed test we do is only as good as the sample we send off, so we want to make sure the sample actually represents the feeds we will be using,” Rusche explains. A sample should be taken from each field, and each cutting of hay, because these cuttings may be different in their stage of maturity.

“If it’s grass hay, we may have started harvest at boot stage and ended up with some fields that were already headed out by the time we finish harvest, and those will be very different in quality. There may also be species differences, or soil differences in certain fields. One field may have had more manure on it, or caught more rain,” says Rusche.

“Then we must make sure we’re sampling that particular lot of hay uniformly and not just pulling cores off the bales we can get to the easiest. We need to take about 20 cores throughout that batch of hay to get a

good representative sample,” he says.

“The labs we send the hay samples to do a good job of testing and reporting. The things we generally look at closest are moisture content, percent dry matter, crude protein, TDN, fiber levels, and associated energy. These values will tell us whether the feed will be adequate to meet cows’ needs, or if certain feeds could be blended together to meet those needs, or whether we need to bring in some outside supplement,” he explains.

Often ranchers just do what they’ve always done. “They might give their cows 35 pounds of dry matter and 2 pounds of protein supplement, but they don’t actually know if they need that supplement,” says Block. “With any unusual harvest conditions, it’s even more important to do feed testing.” A field that normally produces high-quality forage may be different if harvest was delayed by weather (and forage became overly mature) or got rained on multiple times before baling.

“We have published new informational material about rain impacts on forage quality. Some people had trouble putting up hay, and their growing season was different. We saw crested wheatgrass that was still green in August, and it is usually mature and dried out by mid-July. Our growing condition were better in some situations but harvest was not always ideal,” she explains.

“There was some rained-on forage, with loss of quality, digestibility and nutrients. It leached out some of the carbohydrates, vitamins and minerals,” says Block. Some producers baled hay too wet because they didn’t have much choice, and that hay may contain mold and mycotoxins.

If a person is trying to figure out a least-cost feeding strategy and develop an adequate nutrition program, feed testing is the place to start. “Some people call us and say ‘it’s the same field we did last year; can we just use last year’s analysis report?’ I ask them if this year was exactly the same as last year. You don’t really know how different, and we can’t put together a ration with numbers we’re just guessing at,” says Block.

TEST METHODS – Most commercial laboratories offer standard feed tests for forages, grains or total mixed rations. Dr. Rick Rasby (University of Nebraska, Lincoln) says the most important aspects of a feed when designing a diet for beef cattle include assessing moisture content, protein and energy.

Nutrient analyses in a lab are commonly done using chemical reactions or by extracting important compounds and determining their amounts in the feed. Some labs also use near-infrared reflectance (NIR) spectroscopy. This is a rapid, reliable, low-cost, computerized method to analyze feeds.

“This test uses near-infrared light rather than chemicals to identify important compounds and measure their amounts in a sample. Feeds can be analyzed in less than 15 minutes using NIR, compared to hours or days for chemical methods,” explains Rasby.

When sending a sample to be tested using NIR, it is important to identify the type of feed/forage being submitted so the lab can make sure that the right feed library is used. “This method will not accurately evaluate a full mineral profile but does seem to fairly accurately determine calcium (Ca) and phosphorus (P),” he explains.

NIR does not do an adequate job of measuring energy or TDN (total digestible nutrients) content of distillers’ grains, for instance. “In an NIR analysis, TDN is estimated using acid detergent fiber (ADF), which measures cell wall content of a feed. Distillers’ grains are high in fat, and NIR will underestimate energy content. However, NIR will adequately measure moisture, percent crude protein (CP), calcium and phosphorus in distillers’ grains,” says Rasby.

Many labs use NIR tests because they’re cheaper. These are appropriate when testing common feedstuffs like alfalfa, bromegrass, meadow hay or native range hay. With some of the annual forages, however, the NIR tests may not be as accurate. The equation that was developed to predict values was not calibrated for those forages. Spending the extra money to get analyses with wet chemistry for those types of forages would probably be worth it. If you are going to take the time to sample and test your feeds, you want them to be accurate. If you are not sure about how to take or send in samples, or what tests to request, there are nutritionists and other feed experts who can answer your questions.

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