Forage sampling reveals quality

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by Deborah Jeanne Sergeant

Feeding nutritious forage is a vital part of promoting animal health and welfare. Dr. Amanda Grev, forage specialist with University of Maryland Extension, recommends forage sampling and testing to ensure forage is meeting animals’ nutritional needs. She presented “Forage Sampling and Forage Analysis Interpretation” as a recent webinar hosted by MidAtlantic Women in Agriculture and UME.

Defining forage quality is the first step of understanding what nutritious forage should be. “We often use terms like ‘forage nutritive value’ and ‘forage quality’ interchangabley, but forage nutrive value is the concentration of available nutrients, including energy, protein, fiber, minerals and vitamins,” Grev said. “Forage quality is a broader term, and includes nutritive value plus other factors.”

Forage quality is influenced by numerous factors, including palatability. Will animals even eat the forage? Another is intake. How much will the animals eat? Digestibility plays a role. How much of the forage will the animals digest? Nutritive value refers to the nutrition level of nutrients provided once the forage is digested. Anti-quality factors refer to the compounds present that may cause problems.

“Forage quality is the extent to which a forage has the potential to produce a desired animal response,” Grev explained.

Forage quality also has to do with animal performance, whether it’s the animals’ physical actions, how much milk they produce or how much meat they provide.

Determining forage quality can include forage testing and analysis for chemical compounds and a visual assessment; however, Grev said to not use that method exclusively. Even dull-colored hay may have higher quality than green hay, for example. “While visual characteristics are important, it’s important to rely on forage analysis,” Grev said.

For one thing, forage analysis helps gauge hay value. “A forage analysis is beneficial because it assigns market value to forages for purchasing or selling hay,” Grev said. She added that it can also help farmers make feeding decisions such as matching forage quality to animal needs, formulating rations and determining appropriate supplementation. Analysis can also help farmers with limited storage space make more economic storage decisions.

She said forage nutritive value cannot be determined from the feel, texture, smell or appearance of forage, but only with an analysis, which she compares with the Nutrition Facts label on package human foods.

“You may buy a wagonload of haybales and get hay from different places or cuttings, but how you take forage samples is important to consider,” Grev said.

She called hay a “highly variable plant material.” It can be tough to represent an entire wagonload of hay in a single sample. That’s why it’s important to use the correct technique for sampling. Grev recommended using a hay probe, which is 3/8” to 3/4” in diameter and 12” to 24” in length. “Use a core sampler, ideally with a nice, sharp tip with a serrated edge,” she said. “A lot of people want to use a grab sample.”

The problem with that is that they’re typically lower in quality than correctly sampled hay. Grab samples have too many stems and too few leaves to accurately reflect the nutrition of the whole. Farmers should insert the probe fully and perpendicular to the stems. For round bales, that means in the rounded side, not the flat side. For square bales, sample from the butt ends. Grev said to sample a minimum of 20 cores from random hay bales. The final sample size should be about half a pound.

“If you have too much, you can mix those cores together and take a subsample so you have the right amount,” Grev said.

She also said handling the samples is important for accurate results. They should be collected in a labeled plastic bag and stored in a cool location, away from heat and direct sun. Farmers should promptly send in their samples.

Collecting pasture samples involves selecting from 10 to 15 random spots while walking the pasture in a zigzag pattern. Clip the forage down to three to four inches at each location. Combine cut forage and then send about half a pound as the sample. The same handling requirements apply to fresh forage as hay, except that timely delivery is even more important. If the sample cannot get to the lab right away, Grev advised freezing the sample before sending it to the lab to prevent fermentation.

All samples should be labeled with the sample name and number, forage type and date sampled. Accredited labs include those approved by the National Forage Testing Association.

Forage analysis can include wet chemistry tests, which can be time consuming and expensive. Samples may be analyzed only once. Near-infrared reflectance spectroscopy uses light reflectance. It takes little time and is inexpensive. The samples may be re-analyzed. But Grev said it’s not accurate for mineral content of forage. “It’s up to you to decide how simple or complex you want to go,” she added.

Analysis can provide information on dry matter, crude protein, acid detergent fiber, neutral detergent fiber, lignin, ethanol-soluble carbohydrates, water-soluble carbohydrates, nonstructural carbohydrates, starch, calcium, phosphorus, total digestible nutrients, net energy, metabolizable energy and relative feed value.

One of the main reasons farmers want to test forage samples is to measure the net energy they contain. “This means the energy available after digestion,” Grev said. “How much energy was the animal able to extract from that forage?” That energy supports animals’ maintenance or production.

“Quality means more than just what nutrients are present,” Grev said. “It needs to be highly digestible and it needs to be something that is readily consumed so we have a high intake. We want something that’s not too fibrous so they’re not too full.”

It should be between 50% and 60% neutral detergent fiber. The energy should be between 55% and 65%. Protein should be between 10% and 14%.

Grev said forage quality relies upon many factors, including stage of maturity, leaf-to-stem ratio, forage species differences, soil fertility, time of the day and year, harvested or fresh, storage conditions and anti-nutritive factors. Maturity plays a huge role in the nutritional value of forages. For example, more mature plants are higher in fiber.

“Intake is higher when forages were more vegetative and lower when we have more mature forage,” Grev said. “We know that leaves are the most nutrient-rich part of the plant.”

Farmers looking at hay to purchase should examine it for more leaves compared with stems to indicate nutritious hay.

Grev also said legumes tend to be higher in energy and protein compared with grasses.

Harvest and storage techniques also matter for retaining nutrition. Grev shared that plant respiration and conditions during field drying, the proper moisture level during baling and weathering during storage can all make a difference.

The nutrition needs by animal also matter. Grev listed body condition, age, breed, level of production, environmental conditions, activity level and body weight as factors in nutrient needs. A dry cow or idle horse needs far less nutritionally than a lactating cow or a high-performance horse. An underweight animal requires more forage than one that is overweight.

“Make adjustments as needed,” Grev said.

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