Testing required to ensure quality forages

High quality forages supply significant amounts of energy, which results in high feed intake and milk production

GUELPH, Ont. — Forages are the foundation of a good ration for cows, providing roughage, essential minerals and other nutrients.

Forage feeds the rumen microbes, and the cow receives most of the protein and nutrients from rumen microbial fermentation.

“The rumen can exist primarily on forages,” said ruminant nutritionist Mark Bowman of Grand Valley Fortifiers in Cambridge, Ont.

The importance of quality forage and feed testing were explained at the Canadian Grasslands and Forage Association annual meeting held in Guelph last year.

High quality forages supply significant amounts of energy in the form of starch, sugar, digestible fibre, protein and minerals such as calcium, phosphorus, magnesium and potassium, which results in high forage intake, high milk production, healthy cows and lower cost feed.

“Your nutritionist is only as good as your forage quality,” he said.

The rule of thumb for forage intake for ruminants is generally calculated at two percent of body weight.

A 750 kilogram Holstein cow needs 12 to 15 kg of dry matter intake per day, a 600 kg first calver needs 12 kg and a 300 kg heifer or steer needs six kg.

Feed analysis has become more complicated. Testing looks at the levels of neutral detergent fibre and indigestible fibre.

Protein is important, but that can be added with a supplement such as soybean meal.

Acid detergent fibre levels are used less in ration formulation.

ADF is the least digestible portion of fibre in forage. It is highly indigestible and includes lignin, cellulose, silica and insoluble forms of nitrogen.

However, ADF levels are similar in grass and legumes.

Neutral detergent fibre (NDF) is used more in ration formulation. It is the most common measure of fibre, but does not represent chemical compounds. It measures most of the structural components in plant cells such as lignin, hemicellulose and cellulose. NDF levels in a ration influence intake of dry matter and the time of rumination. The concentration of NDF in feeds is negatively correlated with energy concentration.

It provides physically effective fibre to stimulate rumination and cud chewing. Adequate fibre buffers the rumen and helps avoid rumen acidosis.

“NDF is the best measure of insoluble fibre for ruminants,” he said.

“It is related to dry matter intake, digestibility, rate of passage, rumen function and health.”

Measuring NDF digestibility is just as important as total fibre content.

“We want to be able to get some idea before we feed it to the cows and how digestible it will be,” he said.

Higher digestible fibre means the cow will eat more.

There is also fibre that will never be digested.

Alfalfa has more indigestible fibre than grass, but the fibre digestion rate is higher than grasses.

Feed testing laboratories have standard tests, but the industry has done a poor job of explaining what the analysis means, said Dave Tayson of Dairyland Laboratories Inc. with locations throughout North America, including in Calgary, Stratford,Ont., Guelph, Ont., and London, Ont., and internationally.

Today’s programs use a variety of measurements for determining important forage characteristics, including identifying the fibre content of submissions.

“It is important for the end user to understand what the lab can do and more importantly what a lab analysis cannot do,” he said.

The lab can take a sample and add it to rumen fluid in a beaker to see how much fibre was digested and how fast it is broken down. These tests can run up to 240 hours.

The lab looks at Kd, the rate of digestibility in the laboratory, and Kp, the rate of passage out of the rumen.

“Digestibility is the combination of how fast the rumen bugs work and how fast it passes out of the animal,” he said.

Modern ration programs look at digestibility and passage from inputs such as body weight, milk production and dry matter intake and do not necessarily match the individual animal.

“The laboratory can only give you part of the picture,” he said.

The lab measures digestible and indigestible fibre and provides results. Test results showing lower indigestible NDF are best. However, no matter how the diet is formulated or the milk production of the cow, there is a portion of fibre that will not be digested.

Maturity of the forage affects digestibility. For example, lignin levels are higher in mature grass and digestibility is less.

Feed tests also include wet chemistry and infrared reflectance spectroscopy (NIR). Wet chemistry uses laboratory tests to measure protein, fibre, fat and minerals.

The weakest point of NIR is trying to read minerals. Feed testing labs recommend using wet chemistry to determine which nutrients are present, such as calcium and sulfur.

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