How good is that feed?
Interpreting a feed test
Adapted from Chapter 3 in the Sheep Drought Feeding Book on the FeedingLivestock website.
Feeds vary considerably in their nutritional value depending on growing conditions, stage of harvesting and storage conditions. It’s difficult to judge the quality of a feed visually, so it’s important to have feeds analysed to get an objective measure of the quality so you can estimate its value and how much you will need.
The main feed components that can be tested are energy, protein, fibre and dry matter.
Energy
As energy is the main requirement of livestock, knowing the metabolisable energy (ME) values of different feeds is important for two reasons:
- Calculation of the amount of feed required to meet production targets is only possible when the energy value of the various feeds that make up a ration is known
- Deciding to buy feed should be based on the cost per unit of energy rather than the cost per tonne.
A feed analysis report will report on metabolisable energy (ME), expressed as megajoules per kilogram dry matter (MJ/kgDM), sometimes also written as MJ ME/kgDM.
ME is the amount of energy in the feed that is available to sheep for use. It involves measurement of energy excreted in faeces, urine and exhaled as methane. This requires specialised equipment and, in Australia, is not available as a direct measure. Instead, it is calculated based on the digestibility of a feed. Table 1 shows how the energy value can affect the actual cost and the implications for not knowing.
The amount you need to feed will be dependent on how much energy is in the feed. However, if the energy content is too low (and the NDF too high) then the animal may not be able to eat enough. See Useful Tables for sheep (or beef) on the FeedingLivestock website for animal requirements for energy and protein.
Protein
Protein is measured as crude protein as a percentage of dry matter. Protein contains nitrogen, and this is used to estimate the protein content of feeds. A portion of the nitrogen in feed is non-protein nitrogen (nitrates, ammonia and urea); crude protein is a measure of both this and the true protein (amino acids).
Crude protein values give a good indication of whether or not a particular feed will satisfy the protein needs of an animal. Some supplements, such as grain legumes, are high in protein and will be useful if they are cost effective and practical. Supplements that are likely to be low in protein include cereal hays, straws, low-quality pasture hays and some cereal grains. Protein can range from six to 19 per cent in hay.
Silage can show similar variation, and in the case of cereal grains, protein can vary from five to 16 per cent. Lupins are very high in protein and are often added to a cereal grain to increase the protein level of the diet.
Forms of non-protein nitrogen such as urea can be used to increase the rate of digestion of high-fibre feeds such as hay and straw, however, caution is needed as products such as urea can be toxic if consumed in large quantities.
In general terms, at least two-thirds of an animal’s crude protein intake should be provided as true (natural) protein. That is, not more than one-third of the crude protein should be represented by non-protein nitrogen (NPN). These additives should not be included in levels above two per cent of the diet.
Selection of feeds that will meet animal requirements will be dependent on the percentage of crude protein in the diet. For example, if feeding as a sole ration, the protein requirement needs to be at least seven per cent protein for maintenance or above 12 per cent for lactation or growth. See Useful Tables for sheep (or beef) on the FeedingLivestock website for animal requirements for energy and protein
Fibre
Neutral detergent fibre (NDF), as reported via a feed analysis, is a measure of all the fibre (the digestible and indigestible parts) and indicates how bulky the feed is. It is reported as a percentage of dry matter.
A high NDF will mean lower intake. Conversely, lower NDF values lead to higher intakes and tend to have higher energy values. Too little fibre can result in acidosis, as the feed is digested too quickly, and the rumen isn’t able to function properly. Low-fibre, high-starch diets (grains) cause the rumen to become acidic.
The fibre levels of most high-starch grains are generally low. Oats and lupins are both generally higher in fibre and lower in starch. This is why these grains are generally much safer to feed than the cereal grains. Oats are the safest and highest-fibre cereal grain with 29 per cent NDF, compared with barley at 14 per cent NDF and wheat at around 11 per cent NDF.
Cereal grains can be feed in large amounts for long periods very safely, but slow introduction is the key.
Beef cattle need about 30 per cent in the diet as optimal but the level is not well known for sheep and is rarely limiting on pasture. The NDF can be used to estimate how much an animal can eat. The maximum percentage of a sheep’s liveweight that they can eat is 120/NDF. Therefore, a feed with an NDF of 50 per cent means an animal could eat 2.4 per cent of their liveweight (for a 60 kg animal that is 1.44 kg they can eat per day).
Dry matter
All measurements of energy and protein are made on a dry matter basis so feeds of different moisture contents can be compared. Dry matter is the amount of feed left after all the water in the sample has been removed by oven drying. It is expressed as a percentage of the original sample.
Silage has a high moisture content and is around 45 per cent dry matter. This means one tonne of silage has only 450 kg of dry matter and 550 kg of water. Grain has a much lower moisture content, at about 90 per cent dry matter. This means one tonne of grain has 900 kg of dry matter and only 100 kg of water.
Knowing the dry matter percentage enables you to work out how much feed to provide to meet the energy requirements of the stock.
Example: If silage has an energy level of 11 MJ ME/ kg DM, how much silage do you need to feed 10 MJ ME of energy?
Silage required:
10 MJ ME ÷ 11 MJ ME/kgDM = 0.9 kgDM
0.9 kgDM ÷ 0.45 (silage 45% dry matter)
= 2 kg as fed
Other components of a feed analysis
Moisture – measured as a percentage of the original sample, it is the amount of water in the feed. It is what is taken out to give the dry matter reading.
Digestibility – is provided on a feed analysis report as DDM (Digestible Dry Matter) or DMD (Dry Matter Digestibility), depending on the company doing the analysis, and is reported as a percentage of dry matter. It is the percentage of the dry matter actually digested by the animal. High-quality feeds will have a figure over 65 per cent. Feeds below 55 per cent are of poor quality and even if sheep are given free access, they will be unlikely to be able to maintain their live weight if it is supplying all of the diet.
Digestibility of organic matter – DOMD is a calculated figure and is expressed as a percentage of dry matter. It is a measure of the digestibility of the organic component of the feed and takes into account the inorganic component (referred to as ash) such as sand, dirt and clay that may be present in the sample.
Acid Detergent Fibre – ADF is reported as a percentage of dry matter. It estimates the proportion of feed that is indigestible to stock (mainly cellulose and lignin). Feeds with a low ADF are high in energy, and those with a high ADF are low in energy.
Ash – is reported as a percentage of dry matter and is the inorganic portion that is not utilised by the stock. It is any sand, dirt and clay present in the sample.
Fat – expressed as a percentage of dry matter, is a measure of the lipid content of the feed. If the diet of sheep is too high in fat (i.e. greater than five per cent), intake will be reduced.
Water soluble carbohydrate – WSC is reported as a percentage of dry matter and is a measure of the total naturally occurring sugars in the feed. The sugars are a highly digestible source of energy for the rumen bacteria and therefore the sheep.
Note: Not all companies test and report on the same components. Metabolisable energy, protein, neutral detergent fibre and dry matter are key components to have tested.
When sourcing feeds, ask for the feed analysis before you buy. If a test is not available, it may be possible to get a sample and send the test off yourself before deciding whether to buy.
If you buy feed without a test, it is still worth taking a sample and getting a test done so that you can fine tune your rations and assess whether all requirements are being met.
Tools to help
To save doing the maths by hand there are some simple tools to help you make feed comparisons and look at simple cash flow and amounts over time.
For example, the NSW Drought Feed Calculator is an app that allows you to enter three feeds with their Dry Matter, energy and protein contents and the price per tonne. Enter the livestock you want to feed, liveweight, period of feeding and number of animals and it will give you quick outputs of the amount and cost for each feed (including a mix). As an example, I put in four feeds to compare the cost to feed a mob of 3000 dry ewes (60 kg liveweight) for 60 days. Table 1 shows the feeds I used and the calculated cost and amount required to feed (as a full ration).
Table 1 shows that in this example, Feed 2, as a high-quality oat sample, is the cheapest feed at 2.62 c/MJ which translates to a total cost of $36,109 for a full ration over 60 days. This is $19,000 cheaper than the oats with a poorer feed quality. This means that without a test, you could be vastly over or underfeeding (by 30 per cent).
Whilst the lupins (Feed 3) had a very high protein content, as a sole feed, the cost to feed the energy required makes it expensive at $12,000 more in total cost than Feed 2 but could be useful to boost protein levels of low protein feeds.
The hay sample (4) is the most expensive (despite the lowest cost per tome) because of the low energy value and note that the protein level is insufficient. Hays vary enormously and in this season’s report the range for grass hay was 4.4 to 11.6 ME and <0.5 to 20.4 per cent CP, just illustrating the substantial savings and losses to be made.
Table 1. Example of four supplement comparisons to feed 3000 dry ewes (60 kg liveweight) for 60 days
The feed tests results in this table have been sources from actual ranges of samples tested at the FEEDTEST laboratory in the 20/21 season.
| Feed 1 Oats | Feed 2 Oats | Feed 3 Lupins | Feed 4 Pasture Hay | |
|---|---|---|---|---|
| Cost $/Tonne | $330 | $330 | $450 | $300 |
| Energy (ME) | 10 | 14 | 14 | 8 |
| Protein (CP) | 8% | 12% | 30% | 7% |
| Dry Matter | 90% | 90% | 92% | 88 |
| Amount required to feed per head per day | 0.93 kg | 0.61 kg | 0.59 kg | 1.24 kg |
| Total amount required to feed | 167t | 109t | 107t | 224t |
| Total Cost | $55,110 | $36,109 | $48,170 | $67,071 |
| Costs per MJ | 3.67 | 2.62 | 3.49 | 4.26 |
| Comment | Protein inadequate for growing or lactating animals | High protein, but expensive energy | Protein level is below maintenance. |
Animal requirements
For comprehensive tables on what different livestock require, visit the FeedingLivestock website (feedinglivestock.vic.gov.au) and look at Useful Tables (for both beef and sheep) or use the tables in the sheep or beef Drought feeding books from your library or on the website.
Some of the calculators like the NSW Drought Feed Calculator or the Drought and Supplementary Feed Calculator (which you can access on your computer if you prefer) will have these tables built in.