The Principles of Feed Preservation

South Africa is known for seasons where abundant feed production takes place, and seasons where high quality feed is scarce. It stands to reason then that feed should be collected and preserved during the seasons of plenty so that ample feed is available during times of scarcity.

In general, South African livestock farming, especially ruminant production, takes place under extensive conditions. It is in these farming systems that feed preservation is most often practised. In South Africa the most common forms of feed preservation are the making of hay or silage.

In contrast, the production systems of pigs and poultry are intensive. In these systems the feeds provided to mono-gastric animals are manufactured either by the farmer or commercial feed manufacturers. This has allowed the formulation of feeds for mono-gastric animals to the level of precision where particular amino acids are perfectly balanced to meet the requirements of mono-gastric animals at a particular level of production.

Factors Influencing Feed Preservation or Spoilage

The success of haymaking depends on the rapid and almost complete removal of moisture from plant material. It is thus highly dependent on hot, dry weather. Several factors influence the final quality of hay.

These include:

• The type of material from which the hay is produced. Hay made from legumes is obviously higher in protein than hay made from grass or grain materials.
• The growth stage at which the material is harvested. As a plant matures its dry matter content increases, its fibre content increases and its digestibility decreases.
• The method used to make the hay. Methods include, sun-drying, drying in a shed with warm air, drying in a shed with cool air or artificial drying.
• The form in which the hay is fed to the animal. More wastage and poorer intake occurs with hay in the long form, versus hay which has been chopped, ground and pelleted. Hay fed in the long form is also often prone to selection by the animal (in other words the animal selects the tastier bits and leaves the bits that are less palatable). Chopped and pelleted hay also takes up much less storage space.

When feeding hay, the farmer should always be on the look-out for moulds (perhaps if the bale was accidentally wet during storage). Moulds are particularly dangerous to pregnant animals and horses.

The success of silage making depends on the ability to preserve plant material in a wet form. It does not depend on the weather for its success. Several factors influence the final quality of silage.

These include:

• The type of material from which the silage is produced.
• The dry matter content of the material that is ensiled.
• The rate at which the required pH is reached.
• Whether anaerobic conditions in the silage is maintained.
• Whether the silage is protected from rain and sun.
• The size of the particles that are ensiled since this influences the degree to which the material can be compacted and thus has a direct influence on the anaerobic circumstances in the silo.

Feed Quality

Feed quality is dependent on both the original plant material and also how the material has been processed to arrive at the final feed.

Problems That Might Arise in Rations Include:

• Mould growths that can grow on feed crops before or after harvest and on feeds during storage. These may result in the production of mycotoxins (the most important being aflatoxin). Sometimes moulds form in feeds such as maize, peanuts, cottonseed and ryegrass. Some animals such as cattle can tolerate a little mould in their rations, but moulds are particularly toxic to horses and pregnant animals.
• The presence of anti-nutritional factors. These may include:
  • Factors affecting protein utilisation and digestion e.g. tannins
  • Factors affecting metal ion utilisation
  • Anti-vitamins
  • Others such as saponins (Lucerne), cyanogens, alkaloids, photosensitizing agents, isoflavone
• Contamination with poisons or poisonous plants such as oleander can cause problems in mixed or complete feeds
• When plant material is harvested mechanically small animals such as frogs, mice and even snakes may get killed in the process. They end up in the bulk feed bins and are processed along with the feed.
• If the quality of the original plant material is poor then the preserved feed, or the mixed feed ration manufactured there from will also be of poor quality. In this sense poor quality feed may include a raw material like Lucerne that is harvested at a mature stage, when it is very dry and has already lost most of its leaves.

Feed Preservation Techniques

Silage

Click here to view a video that explains good practices for silage production.

The normal process of making silage depends on the transformation of soluble carbohydrates in the plant (or which are added to the silage) into lactic acid so that the pH of the silage drops to approximately 3.8 to 4.2. Well-made silage has a lactic acid content of approximately 8 to 12% of dry matter. Silage at a pH of 4 is stable and can be preserved indefinitely as long as the anaerobic conditions in the silo are maintained. If rain enters the silage or if the lactic acid concentration is too low, then a secondary clostridium-type fermentation ensues where lactic acid is converted into butyric acid. Silage in which this spoilage has occurred has a pH higher than 5 and has a bad taste and smell. Because this secondary type of fermentation can only take place in the presence of moisture, it is often recommended to wilt the plant material before ensiling and in this way reducing the moisture content of the plant material to between 65 and 70%. If the plant material, which is to be ensiled, does not contain enough carbohydrates (for example, if Lucerne is to be ensiled versus the more common maize silage), then external carbohydrates can be added. This can be done by adding 2 to 3 percent molasses to the mixture and mixing well (20 to 30 kg of molasses per ton of silage) or by adding 45 to 55kg of maize meal to the mixture and mixing well. A well-made silage smells of fresh apples.

Any moisture rich material can be ensiled if adequate carbohydrates are available. Also, the material must be chopped fine enough to allow effective compaction to ensure that anaerobic circumstances are maintained in the silo. Materials as diverse as the leaves and trunks of banana trees, a mixture of oranges and cabbage, cosmos flowers, sugar cane tops, citrus pruning, and mango pruning have been successfully ensiled during research aimed at small scale farming at the Animal Nutrition and Products Institute of the Agricultural Research Council at Irene.

Drying

Plant material should be cut several times during the growing season. The quality of the hay is directly dependant on the stage of maturity of the plant when harvested: the younger the plant the higher the final hay quality will be. However, it must be remembered that younger plants are higher in moisture and thus that the drying process will take longer. Drying takes place on hot, sunny days, and ideally with a light breeze. The hay rows should be turned on the land several times to allow the hay to dry on all sides. When the hay is completely dry it can be raked and baled. Hay should be stored out of direct sunlight and away from moisture and pests such as birds and rodents.