1.2.1  Physical evaluation

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.

Colour

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

Size

Size of the grains governs its energy value due to the proportional  decrease/increase in seed and its coat. Smaller the grain, lower  will  be the metabolizable energy (ME) value due to more proportion  of coater hulls. To evaluate the cereals, weight of a fixed number of grains usually 100 grains or fixed volume is taken. Higher weight indicates a higher ME value. This technique is called Test Weight.

Homogeneity

The presence of contaminants like other grains, husk, broken grains, weed seeds, infected seeds is viewed. In the oil seed cakes closer observation will reveal the presence of fibrous material, especially in de-oiled groundnut cake. Rice polish is contaminated with husk. Clumps in mineral ingredients are not suitable 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 plant manager should familiarize himself with the normal smell of the ingredients; any change in the normal smell of the ingredients should be viewed with suspicion. Musty odour indicates the beginning of fungal contamination or boring insects. To detect rancidity in oil rich feed ingredients this is the best method. Odour of petroleum products is suggestive of excessive pesticide or fungicides.

Taste

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

Touch

Feeling the raw material will  indicate dryness. Chilliness indicates high moisture content. Clumps can be detected by inserting a hand inside the bag. Clumps may be formed due to high moisture content, improper storage, packing of fresh warm solvent extracted meal, which crumbles on application of light pressure. Clumps formed due to excess of 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 per cent. 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 on pouring down or biting will produce sound of spilling coins.