Physical Evaluation of Feed Quality

Ingredient Quality (Qualitative)

Physical characteristics (analyst’s skills) Colour, Texture, Odour and Taste, Particle size (screen analysis), shape, Adulteration, damage and deterioration, bulk density, storage pests, hairs etc, spot chemical tests,

A physical evaluation is easy but rough in nature. One must be highly trained to identify the changes in the nature of the raw materials/feeds. Usually, the following criteria are investigated:

Colour - The appearance of the ingredient will reveal its quality. Any change in the colour of the feed ingredients gives an indication of the maturity of the grain, storage conditions, presence of toxins, and contamination due to sand, possible use of insecticides/fungicides which gives a dull and dusty appearance. The Orange to red colour of sorghum indicates high tannin content. Browning or blackening due to heat on improper storage reduces nutritive value. Black coloured fish meal indicates the rancidity of fish oils.

Size - The size of the grains governs its energy value due to the proportion of decrease/increase in seed and its coat. The smaller the grain lower will be the protein value in proportion to the hulls. To evaluate the cereal's weight of a fixed number of grains usually 100 grains or a fixed volume is taken. A higher weight indicates a higher protein value. This technique is called Test Weight.

Homogeneity  - The presence of contaminants like other grains, husks broken grains, weed seeds, and infested seeds is looked for. In the oilseed cakes, closer observation will reveal the presence of fibrous material, especially in de-oiled groundnut cake, the cake with hulls which contains nearly 20 to 25 % crude fibre can be visually identified. Clumps in mineral ingredients make them unsuitable for premixing.

Smell - Smell is the next best indicator just standing near the stock itself will immediately indicate any difference in the normal smell. The feedlot manager should familiarise himself with the normal smell of the ingredients, any change in the normal smell of the ingredients should be viewed with suspicion. A musty odour indicates the beginning of fungal contamination or boring insects. To detect rancidity in oil-rich feed ingredients this is the best method. An odour of petroleum products is suggestive of excessive pesticides or fungicides. A leathery smell of meat indicates adulteration with leather meals.

Taste -  Each ingredient has a different taste, any change in the taste like bitterness in the grains, soya, sunflower oil meal and groundnut cake might indicate the presence of mycotoxins. The level of salt can be detected by tasting the ingredient and the feed. The bitter taste of rice polish indicates the rancidity of the fatty acids.

Touch  - Feeling the raw material will indicate dryness. Chilliness indicates high moisture content. Clumps can be found by inserting the hand inside the bag. The clumps may be due to high moisture content, improper storage, or packing of fresh warm solvent extracted from the meal, which crumbles on the application of light pressure. Clumps formed due to excess moisture will be very hard. To evaluate rice polish, place about 25g of rice polish on the palm and close the fingers tightly and then open the fingers, the rice polish will become like a solid mass if the crude fibre level is below 12% if the fibre level is high the mass will disintegrate once the fingers are opened. Further pressure will be felt when the hand is closed in high fibre rice polish.

Sound - Dry grains pouring down or biting will produce the sound of spilling coins.

Detection of Adulteration or Contamination  - The common contamination or adulteration in most ingredients is husk or sand. Winnowing is the best method to detect husk in feedstuff. Sieving can be done to differentiate contaminants based on particle size. To detect the presence of sand a weighed quantity of the grain is soaked in water then by sieving with hand the grains that be separated. The remaining water decanted from the settled sand can be weighed and the level of contamination can be assessed.

When determining the quality of feeds or ingredients, the first step is to check the feeds for adulterants that can affect the digestibility of the feed.

Heat Discharge

Another important factor that is used when assessing feed is the heat discharge factor. Heat discharge is commonplace and takes place when the moisture content of ingredients is too high. A high moisture level in ingredients usually leads to fermentation of those ingredients and a by-product of the fermentation process is the release of heat.

Whilst feed and ingredients have been assessed the presence of heat should be immediately reported to the feedlot manager or operator as this might be an indication that the feed is not suitable for use. It is always good practice to ensure that all staff involved in the mixing and distribution process of the feed should be trained to look for heat discharge in the feed and report it when found.