Forage preservation can be an attractive alternate to cover farmer feed problems to ensure regular supply of fodder even in periods of acute shortage to get optimum production from dairy animals. The practice necessitates on the crop to be preserved, stage and method of harvesting, type of storage structure and consistent high-quality management practices implemented before and during the process.

Harvesting fodders as silage in succulent conditions is a compromise between reducing labour requirements and field losses versus losses in the fermentation process. In western countries, silage making is practiced by almost every dairy or beef cattle farmers while in Pakistan practiced mostly on military dairy farms.

Silage is the product resulting from storage and fermentation of fresh forage under anaerobic conditions producing 30-50 per cent more forage and nutrients per unit area than the same crop converted into grain and crop residue increasing the carrying capacity of a farm.

Crops used for silage are oat, maize, berseem, sorghum and grasses. Moisture content, length of chop, silage distribution and compaction can greatly influence fermentation process and storage losses. Efficient fermentation ensures a more palatable and digestible feed which encourages optimal dry matter intake that translates into improved animal performance.

Microbes (bacteria) responsible for fermentation need anaerobic (in the absence of air) conditions. As bacteria consume sugars, end-products produced (acetic and lactic acid) cause the pH to drop. Quality silage is achieved when lactic acid is the predominant acid produced, as it is the most efficient fermentation acid and will drop the pH of the silage. Ffaster the fermentation is completed, the more nutrients will be retained.

Management of silage depends upon maturity and moisture contents of the crop, length of cut, filling, packing and sealing techniques and the type of additives used. Recommendations vary with different silage crops. Proper maturity assures adequate fermentable sugars for silage bacteria and maximum nutritional value for livestock. Maturity also has a tremendous impact on moisture with unwilted forage crops such as corn silage. Adequate moisture for bacterial fermentation is essential and aids in packing to help exclude oxygen from the silage.

The most desirable length of cut is between ¼ to ½ inches depending upon the crop, storage structure and amount of silage in the ration. This will give ideal compaction of the silage and yet allow for ease of unloading from an upright silo. Chopping forages too long makes compaction difficult and air will remain trapped in the silage resulting in heating and spoilage. Filling, packing and sealing method play a key role in silage management.

Crop should be harvested and the silo filled as rapidly as possible. Filling delays will result in excessive respiration and increased silage losses. Packing should begin immediately when storing silage in bunker silos. A wheeled tractor is preferred as a packing vehicle, as it will supply greater weight per unit area than a tracked vehicle. Silo should be sealed with an air-tight cover once it is filled to prevent penetration of air and rainfall into the silage. Face management requires skill. The silage face should be maintained as a smooth surface, perpendicular to the floor and side walls in bunker and trench silos. This technique will minimize the square footage of surface exposed to air.

An average daily removal rate of 6 to 12 inches from the face should prevent heating and spoiling of exposed silage. Well-packed silage reduces the distance that oxygen can penetrate in an exposed silage face. Various additions to silage have been suggested to improve or alter the fermentation process. These materials may be referred to as additives, conditioners and preservatives.

Benefits obtained from silage additives, conditioners and preservatives depend upon their influence on the silage fermentation process. These benefits are usually measured by the reduction in fermentation losses and improvement in silage quality and feeding value. Silage additives, conditioners and preservatives function in the following ways

Add dry matter to reduce moisture content, alter the rate, amount and kind of acid production, acidify the silage, inhibit bacterial and mold growth, Culture silage (inoculants) to stimulate acid production, increase nutrient content of the silage.

The objectives of adding dry matter to moisture content is to provide a more suitable medium for the fermentation process. The goal of producers should be to harvest corn and sorghum for silage at the proper growth stage or at physiological maturity when plant moisture content is ideal. Grasses and legumes should be wilted or dried to an average of about 65 per cent moisture or less depending on the type of storage used.

If forage crops must be harvested too wet for silage, the following guideline for dry matter addition may be used. Cereal grains, coarsely ground and chopped, air dry alfalfa or grass forage will decrease the moisture content of wet forage approximately five percentage units for each 150 to 200 pounds of material added per ton of wet forage weight.

However, if forage crops to be stored as silage become too dry, packing to exclude air is difficult. Under such conditions, water must be added to raise the moisture content to the desired level or severe dry matter losses will result. The amount of water required to increase forage moisture content is approximately 5 to 6 gallons per ton of ensiled material.

Acid production is essential in keeping the qualities of silage. The rate, amount and kind of acid produced are influenced by the moisture content of chopped forage and the readily available carbohydrate content of the forage.

Since silage is a product resulting from the action of bacterial enzymes on the material stored, attempts have been made to alter/regulate silage fermentation through the addition of materials containing bacteria, yeasts and moulds. The primary purpose for adding bacterial inoculants is to increase the number of lactic acid-producing bacteria, encouraging more lactic acid production and well-preserved forage mass.

A number of commercial products, referred to as fermentation aids and/or inoculants, are available for adding to silage at the time of ensiling. Research using various bacterial inoculants indicates highly variable results.

Products showing consistent, positive results indicate about five per cent increase in dry matter preservation. Therefore, cost of the inoculants per ton compared to the dollar value of the dry matter saved will determine the profitability of using silage inoculants.

Various materials added to silage will increase nutritive value to the extent that they contain nutrients. Increasing the nutrient content of silage will greatly affect the final cost of the product produced. Materials such as cereal grains, molasses, dry forages, limestone, urea and anhydrous ammonia are examples of nutrient additions to silage. Commercial products are also available that contain one or more of the above materials.

Advantages Silage produces 30-50 per cent more forage per unit area and, therefore, increases the carrying capacity of the farm, generates 30-50 per cent more nutrients per unit area than the same crop converted into grain and crop residue. Its nutritional value is unchanged for the entire feeding period without dependence upon weather or the period of the year. It is the most economical, requires three times less storage space (calculated on DM basis) than hay, even when baled or chopped and cannot be destroyed by fire, facilitates preservation of crop residues, by-products and wastes, and increases their palatability and enhances the intake by providing succulent feed during dry periods, during the time of feed scarcity, especially when vegetal growth is dormant.

It facilitates utilisation of animal wastes (poultry litter and cattle manure) as a safe system in eliminating pathogens including nematodic parasites, which normally survive conventional drying or even sterilisation processes and also saves forages or crops damaged by storm or other disasters, because they can be collected, in case of emergency, at any stage of plant development.

The nutritional value of the herbage is preserved in the most efficient way.

Disadvantages It requires silo storage structures, which may be costlier than hay making; particularly at small farm levels, poorer in vitamin D than hay and dry matter losses (5-30 per cent%) may occur as a result of a prolonged aerobic phase due to poor packing of silage during its preparations and management.