Evaluation of feedstuff

In the feed manufacturing process evaluation of the feed ingredients is very important in achieving consistent quality throughout the year. If one is able to assess the quality of the ingredient before it is unloaded from the truck it will save time and money. There are different types of evaluations, which can be done easily and quickly. Physical, chemical and biological are the three evaluation methods.

Physical evaluation

This is the easiest and important method of feed evaluation. The nutritionist or the mill manager should train himself to use all his five senses to identify the following changes in the nature of the raw material

Sight Colour: Each feed ingredient has its own characteristic colour. The appearance of the ingredient will reveal its quality. Change in the colour of the material gives an indication of the storage condition, presence of toxins, etc.
Size: Size of the grain is a good indicator of the energy value. Smaller the grain  lower will be the ME value, since the seed coat part will be in increased proportion. Hence, to evaluate the cereals, weight of a fixed number of grains can be used; especially weight of one hundred grains or weight of one liter of the grains will give a good indication of the density of the grains.
Homogeneity: Here one has to look for the presence of contaminants like other grains, husks, etc. Further, in the cakes also closer observation will reveal the presence of fibrous material; especially in de-oiled groundnut cake the cakes with hulls which contain nearly 20 to 25% crude fiber can be visually identified.Presence of un-wanted substances in feed ingredients like sands, rat pellets, insects,
leather mill in meat-cum-bone meal, etc.

Smell
Smell is the next best indicator. Just standing near the truck itself will immediately indicate any difference in the smell. The mill manager should familiarize himself with the normal smell of the ingredients; any change in the smell should be viewed with suspicion. Musty odour indicates the beginning of fungal contamination. To detect rancidity in oil rich feed ingredients this is the best method.

Taste
Each ingredient has a characteristic taste; any change in the taste can be detected. Bitterness in the grains, soya, sunflower oil meal and groundnut meal indicates the presence of mycotoxins. The level of salt can be detected by tasting the ingredient and the feed.

Touch
Feeling the raw material will indicate the dryness, chillness indicates high moisture content. Clumps can be found out by inserting the hand inside the bag, all clumps need not be due to high moisture content or improper storage, but due to packing immediately fresh warm solvent extracted meal. These clumps will crumble on application of light pressure, but those 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 fiber level is below 12%, if the fiber level is high the mass will disintegrate once the fingers are opened further, pressure will be felt when the hand is closed in high fiber rice polish.

Sound
The sound like spilling of the coins when the grains are poured down indicates dryness, and when the grain is bitten the sound will also indicate the dryness.Physical methods to detect adulteration or contamination Following simple tests are carried out to evaluate the ingredient before unloading.

a.  Test for sand level: weighed quantity of the material is mixed with water. The sediment sand can be appreciated after removal of  material and decanting of  water.

b.  Test for husk level : by winnowing
c.  Sieving : differentiates contaminants by particle size
d.  Test weight: measure of unit volume weight or weight of specific number of grains. High weight per unit volume or per grain indicates higher nutritive value.

Chemical methods of evaluation
Detailed chemical analysis in the laboratory will give an idea about the ingredient. But, chemical tests will be time consuming hence the mill manager should be dependent upon some spot tests to take immediate decision.
SPOT TESTS: A few spot tests for quick evaluation have been given below.

1.  Salt (sodium chloride)

Reagents:
1.  Silver nitrate solution (5%).
2.  Nitric acid solution (1:2).
3.  Ammonium hydroxide solution (1:1).
4.  Standard sodium chloride solution (0, 0.1, 0.2, 0.3 %).

Procedure:
1.  Weigh 1g of sample and add 100 ml of distilled water. Stir and filter with
Whatman No.4
2.  Pipette 1 ml of standard solution and 8 ml of nitric acid solution.  Stir and add 1 ml of silver nitrate solution.
3.  Stir and compare the test sample with the standard sample. This test should
be read within 5 minutes.

Positive results:
Salt gives WHITE TURBIDITY.

2.  Urea

Reagents:
1.  Urease solution – Dissolve 0.2 g of urease powder in 50 ml of distilled water.
2.  Standard urea solution (0, 1, 2 …5%)
3.  Cresol red indicator (0.1%).

Procedure:
1.  Weigh 10 g of test sample and add 100 ml of distilled water.  Stir and filter with Whatman No.4
2.  Pipette 2 ml of standard solution and test sample into white porcelain spot
plates.
3.  Add 2-3 drops of cresol red indicator and add 2-3 drops of urease solution.
4.  Let it stand for 3-5 minutes, if urea is present, it will form a deep red-purple spreading like a spider’s web appearance, in contrast to the yellow color of the indicator.
5.  Compare the test sample with the standard urea sample. This test should be
read within 10-12 minutes.

3.  Measurement of quality of soybean meal
 
1.  Cresol red qualitative test for under processing

Reagent - Cresol red solution
80 mL of cresol red 0.1% solution (0.08g cresol red in boiled and cooled water)
20mL glycerol or sorbitol to increase viscosity
2g urea
Few drop s of thymo l blue (0 .1% a lcoho lic solution) to check microb ial decomposition
Mix cresol red, solution, glycerol, urea and thymol blue. Sample: Particle size 200m

Procedure: Spread the sample uniformly on petri dish, glazed paper with white background. Spray reagent solution over the particles.

Interpretation:
Observation Activity of trypsin inhibitor
1.    Few red particles    slightly active
2.    25% covered with red particles    moderate
3.    50% covered with red particles    Active
4.    75 % covered with red particles    Very active
5.    No red particles    Over cooked
4.  Hoof or horn

Reagents: Glacial acetic acid (1:1).

Procedure:
1.  For quick test, place 2-3 particles of amber color test sample into an evaporating dish.
2.  Add 5 ml of glacial acetic acid into the evaporating dish and let it stand for 60 minutes.
3.  If hoof and horn are present, the test particles will still remain hard and tough. 

4. Gelatin will be become soft and swollen.
5.  Leather meal

Reagents:
1.  Ammonium Molybdate solution – Dissolve 5 g of Ammonium Molybdate in 100 ml of distilled water and pour into 35 ml of concentrated nitric acid.

Procedure:
1.  Pick up brown to black test sample particles and place in petri dish.
2.  Add 3-5 drops of ammonium molybdate and let it stand for 5-10 minutes.
3.  Leather meal will give no color change. Meat and bone meal gives a greenish yellow color.

Laboratory analysis
A feed mill should necessarily have a feed analytical laboratory to precisely estimate the nutrient content and contamination of the feed ingredients. Further, contamination of fungal toxins has become a regular feature; hence the present situation warrants that all feed mills have a good feed analytical laboratory.

 
Mycotoxin: Contamination of feedstuffs with mycotoxin is a global problem. The  mycotoxins may occur when the fungi grows on crops in the field, at harvest and / or improper storage or processing (improper drying to less than 11% moisture). Some of the mycotoxins observed in poultry feeds are aflatoxins, ochratoxin, zearalenone, T2 toxin, fumonisins etc. Aflatoxin B1 is the most prevalent mycotoxin and this is mainly produced by the fungi Aspergillus flavus and A. parasiticus species. Ducks are highly sensitive to aflatoxin. Mycotoxin presence in feedstuff cause economical loss to poultry producers by affecting the productive performance (egg / meat) and the immune- competence of birds. Feedstuff like grain harvested in moisture season and improper storage of grain (presence of mould growth or black spot) and groundnut cake are in general screened for mycotoxin content. Compounding of poultry rations is attempted to avoid this mycotoxin or to minimize its level in the finished product. Rations, compounded with minimal level of Aflatoxin, are generally protected with toxin binders and liver stimulants.

Evaluation of fat and oil: Fat and oil are evaluated for rancidity, free fatty acids, unsaponificable material, degree of saturation and chain length of the fatty acids.Test for rancidity one is the free fatty acid level indicating the hydrolytic rancidity and the other is the peroxide value which is the test for oxidative rancidity. In case of hydrolytic rancidity there is only reduction in the nutritive value in oxidative rancidity it will not only lose its nutritive value but the free radicals may affect the health and productivity of the birds.