Nutrient requirements are influenced by many factors, such as weight of animal, sex, desired rate of growth, stage of lactation, environment and others.
The nutrient composition of a feed is the amount of specific nutrients contained in the feed. They are expressed as a percentage of the dry matter and may also be found in published feed composition tables.
- Dry matter
Dry matter is the portion of the feed left after all water has been removed. It contains the nutrients. Values for dry matter intake shown in nutrient requirement tables are not all an animal will consume, but represent an amount that can be consumed under normal circumstances.
Different feeds contain different levels of dry matter; therefore, it is desirable to balance the ration on a dry matter basis and then convert the various feeds back to an as-fed basis.
- Crude protein
Crude protein which is also called total protein is determined by measuring the nitrogen content of feed and multiplying by the value 6.25 because proteins typically contain 16% nitrogen. Not all nitrogen-containing compounds are true proteins. These are called nonprotein nitrogen (NPN) sources.
Many of these NPN compounds can have their nitrogen converted to microbial protein in the rumen under proper conditions.
Generally, NPN sources are not used well as protein when cattle are on high roughage rations or have high protein requirements, such as young cattle with high rates of growth. True protein sources should be used in these cases.
Energy is not essentially a nutrient; it is contained in nutrients such as carbohydrates, fats, etc. It is for practical purposes that energy is considered a nutrient. There are several methods of measuring feed energy values. Some of these are digestible energy, net energy for maintenance and gain and total digestible nutrients. Total digestible nutrients (TDN) is the value most commonly used in simple ration balancing.
Minerals are compounds needed to regulate many metabolic functions in the body. They may be classed as macro or trace minerals depending on the amounts needed. Examples of macro minerals are calcium and phosphorus. Iron, zinc and copper are examples of trace minerals.
- Vitamins and water
Other important nutrients are vitamins and water. Rations are not normally balanced for these nutrients, but adequate amounts must be provided for desired rates of growth. Water is particularly important because feed intake decreases when water intake is not adequate.
Roughages are feeds that are relatively high in fibre and low in energy. Hay, straw, cobs, cottonseed hulls and corn stalks are examples of roughages.
Concentrates are feeds or mixtures of feeds that are relatively low in fibre and provide energy as the primary nutrient.