Let us summarise some of the facts about rationing which you have learnt in this course.

  • Animals are rationed for two reasons:
  1. to satisfy their requirements for a particular purpose
  2. to utilise the available food to the best advantage.
  • Protein is expressed as kg of Crude Protein, or C.P., or as kg of digestible crude protein, or

D.C.P. This is supplied in the protein eaten by the animal. Ruminants can use both the true protein in foods and also the simple nitrogenous compounds called amides; they can also use urea as a source of protein.

  • Energy is expressed as kg of total digestible nutrients, or T.D.N. This is supplied by the carbohydrates, fats and part of the protein eaten by the animal.
  • Energy can also be expressed as metabolisable Energy (M.E.), measured in MegaJoules per kg of feed. An approximate conversion from one method to the other is that one MJ/kg of ME is equivalent roughly to 6.7% TDN. For example 10 MJ/kg of ME would be about 67% TDN. In these lectures we have worked mainly in TDN.
  • Minerals are expressed as kg or gram of the particular mineral – calcium, phosphorus, etc. Calcium and phosphorus are the most important minerals, particularly for milking cows and young, growing animals. Cereals and oil seed cakes are low in calcium and high in phosphorus, whereas grass, hay and silage are high in calcium and low in phosphorus. All purchased concentrates contain added minerals, but rations mixed on the farm should include a mineral supplement. A usual mineral supplement for milking cows is:
  1. 13.5kg of steamed bone meal;
    1. 11.0kg of common salt;
    1. 20.0kg of limestone flour and;

4. + Trace Elements.

  • These are added to a concentrate mixture at a rate of 1kg for every 50kg of concentrate.
  • Vitamins are expressed in International Units. Ruminant animals should not suffer from vitamin deficiency, but it is a common practice to add vitamin A and D to winter rations. Pigs and poultry which are kept in houses at all times should be fed a vitamin supplement in their rations.
  • The appetite of an animal is measured by its daily intake of dry matter. For cows, this is 3% of bodyweight, and for beef cattle, 2.5% of bodyweight.
  • Foodstuffs are classified into the following groups:
  • Dry Roughages which are hay, straw, maize, stover, etc.
  • Succulent Roughages which are silage, young veld grass, pasture grass, green oats, lucerne, etc.
  • Roughages are used to provide the maintenance part of the ration for cattle and sheep although good quality roughage will provide some production.
  • Concentrates which are used to supply most of the production requirements for dairy cattle, some beef cattle, pigs and poultry. Concentrates are divided into:
  • High Energy, Low Protein – these are the cereals such as maize, barley, oats, wheat, sorghum, etc.
  • High Energy, High Protein – these are the oilseed meals and cakes such as soybean meal, groundnut cake, etc.

Besides supplying nutrients (energy, protein, minerals and vitamins) to animals, there are a number of other factors which have to be considered when making up rations.


These pass quickly through the digestive tract of the animal before digestion and absorption can take place and the animal fails to get the benefit of the food. Laxative foods are succulents such as silage, young grass, etc., and foods that are rich in oils and amides. Wet bran is a laxative that can be fed to sick animals.


These are foods which cause animals to become constipated and so prevent the complete elimination of waste products from the large intestine and rectum. Such foods are those high in fibre such as hay, straw, stover, and un-decorticated cotton cake. Bran and sugar beet pulp, if fed dry, absorb water and have a costive effect.


This is important in rationing because although a ration may be balanced for nutrients, if the animal does not like the ration and will not eat it, the ration will be of no use. Succulents and foods rich in sugars, oil, and protein are the most palatable. Dry fibrous and mealy foods are least palatable. Heavy meals like maize, wheat, and barley can be mixed with lighter meals like bran, oats and flaked maize to improve palatability. Salt, molasses, locust beans and aniseed can be added to rations and the palatability can be affected by the preparation, such as the grinding, milling and mixing.


Animal products can be tainted and this can be caused by bad feeding. Poultry, meat and eggs can be affected by feeding too much fish meal in the ration which will give it a fishy taste.

Milk is very liable to be tainted and this can be caused both by feeding and by leaving milk in a container with no lid where it will absorb taints from the air. Cows that graze garlic will give milk that has a taste of onions. Feeding too much kale or too many turnips can give milk a taint, and milk left in an open container can pick up the taste of silage or creosote from the smell in the air.


The type of fat which is fed to an animal is important, particularly with pigs and beef. You may remember from the lectures on digestion that fats which are eaten by any animal are broken down into glycerol and fatty acids. There are 29 fatty acids, the most important ones being:

  • Formic Acid
    • Acetic Acid – vinegar
    • Propionic Acid
    • Butyric Acid – found in milk and butter
    • Lactic Acid – found in milk

There are two types of fatty acids; saturated, which are fats or solids at normal temperatures, and unsaturated fatty acids which are oils or liquid at normal temperatures. Foods which contain a high proportion of unsaturated fatty acids will produce a soft, oily fat in pigs. Foods containing saturated fatty acids produce a firm hard fat in pigs.

Hard fat is produced by: barley, wheat, pea or bean meal

Soft fat is produced by: maize, soybean meal, groundnut meal

The type of fat fed to a cow can affect the appearance of the butter made from that cow’s milk.

In ruminant digestion, fatty acids are produced by the breakdown of food in the rumen, and many of these are absorbed by the animal directly through the wall of the rumen. The type of fatty acid produced can be affected by the food which the animal eats. Fibrous foods such as roughages like hay and stover increase the amounts of acetic acid in the rumen, whereas starchy foods, and especially flaked maize which has been cooked, reduce the acetic acid and increase the proportion  of the propionic acid. The same effect, i.e. reduced acetic acid and increased propionic acid, is produced by reducing the amount of roughage and increasing the concentrate (mainly cereal) in the ration.

In experiments in which the amounts of roughage in the ration of fattening steers were varied, liquid was removed from the rumen and analysed for fatty acids and tested for pH, the results were as follows:

Roughage in RationAcetic AcidPropionic AcidpH

You can see quite clearly that as the roughage was reduced so the concentrate increased in the ration. The acetic acid is reduced and the propionic acid is increased in the rumen. In addition the pH falls, showing that the contents of the rumen become more acid. If too much concentrate is fed, the rumen pH becomes too low and the animal loses its appetite. This is why cattle which are being fattened in pens on high concentrate rations must have some roughage in order to keep the rumen functioning properly. It is also important to include an ant-acid like limestone flour in the ration to help neutralise the high acidity.

The amounts of the different fatty acids in the rumen are important in milk production because they have different effects on the milk produced by the animal.

High proportion of acetic acid INCREASES both milk and butterfat production.

High proportion of propionic acid REDUCES butterfat and INCREASES the solid not-fats and protein

in the milk.

Furthermore, while acetic acid is good for milk production, propionic acid is good for the fattening of the animal. This is a basic difference in the metabolism of the milking animal and the fattening animal. It is the reason why animals can be fattened on low roughage, high concentrate ration (high- energy diets), while this type of ration is unsuitable for milking cows. Cows fed on high-energy diets will produce body fat rather than milk.