Feed quality – what do those laboratory reports mean?

Feed quality – what do those laboratory reports mean?

24 February 2020

We can’t manage what we don’t measure. Feed testing is a valuable way to assess feeds offered to stock, to decide if a feed is suitable for your animals and to help deliver a balanced diet.

Feed testing laboratories provide so many numbers to describe the quality of feed. What do these values mean and how can we use this information on farm? Charlotte Westwood, Veterinary Nutritionist, at PGG Wrightson Seeds explains the importance of these feed quality values.

Dry matter (DM) percentage

The dry matter (DM) content of feed means the proportion of feed that is DM, with the balance of feed present as water. The wetter the feed, the lower the DM percent. All feeds contain water, even dry feeds. Palm kernel extract (PKE) contains 90 percent DM, which means every one kilogram (kg) of PKE contains 900g of DM of and 100g water. If we know the DM percentage of a feed, we can convert weight of feed on an ‘as fed’ basis (that is, how much a feed weighs e.g. in a feedout wagon) to a DM basis. This is useful for silage and baleage so we know how much DM is in a loaded silage wagon that measures wet weight/load, or how much DM is in a bale of baleage.

Megajoules of metabolisable energy (MJME)

This is the energy content of feed and is reported together with digestibility. The MJME value is (usually) calculated from the digestibility value. The MJME value describes how much of feed energy is available (digestible) for the animal to complete beneficial functions such as grow, produce milk, and to support milk or wool production or pregnancy requirements. High MJME values (up to 13 MJME/kgDM) mean a feed is good quality and is suitable for supporting top animal performance. Low MJME values (less than 7.5 MJME) mean a feed a less suitable for feeding to animals.

Crude protein (CP)

Multiplying the nitrogen (N) content of feed by 6.25 gives us the CP content. Some feeds are normally low in CP, for example feed grade molasses (six percent CP), maize silage (eight percent CP) or fodder beet bulbs (eight percent CP). Other feeds contain lots of CP, including soybean meal (up to 48 percent CP). Good quality leafy greenfeeds contain moderate to high CP levels including top quality lucerne or mixed ryegrass/white clover pasture (up to 30 percent CP).

CP content of feeds is important; low CP feeds may not support the needs of young growing, lactating or pregnant animals. High CP is important environmentally because surplus dietary CP increases risk of loss of urinary N to waterways.

Neutral detergent fibre (NDF)

Ruminant farm animals need sufficient dietary NDF to support stable rumen function. Probable DM intake by stock can be predicted based on the NDF of an animals’ overall diet. Fibre requirements of animals vary, with minimum required NDF levels of 28 percent NDF (sheep) and 35 percent NDF (cattle). Low NDF feeds include feedgrade molasses (zero percent NDF) and kibbled maize (10 percent NDF). High NDF feeds include cereal straws (up to 75 percent NDF).

Water soluble carbohydrates (WSC, or ‘sugar’)

Farm animals like and need minimum amounts of dietary WSC. Higher WSC feeds include molasses; examples of low WSC feeds include PKE and poorly made pasture silage. Pasture content of WSC can be variable, changing with stage of season and WSC levels in pasture can vary from morning (low) to afternoon (higher) due to photosynthesis increasing WSC content of pasture during the day.

Starch

Found in many feeds commonly fed to ruminants, starch is a good source of energy. More starch is better for animal production, but too much starch causes rumen acidosis. Starch level is close to zero for some feeds (PKE, lush leafy pasture or pasture silage) but high in other feeds such as wheat grain (65 percent starch) or potatoes (75 percent starch).

Many other results reported by feed laboratories are equally as important as the values outlined above. Mineral profiles are important when deciding if feed is suitable for young growing, pregnant or lactating stock. The acidity of a silage sample (pH) and lactic acid content tells us the extent and success of the ensiling process.

For more information on feed quality, talk to your local TSR or visit your local Farm Source store.

Article supplied by PGG Wrightson Seeds