Feed adulterants

Adulteration of raw material is creating a serious problem for manufacturing the good quality feed as the trading of raw ingredients is totally in unorganized sector. Possibilities of adulteration are more in costly feed ingredients like oil cakes and feed products of animal origin like fish meal. Cheaper ingredients are usually not adulterated as it may not be remunerative. However, in case of high prices of cheap ingredients like brans and molasses, these are also adulterated by some unscrupulous traders. Adulteration cannot be easily detected by the farmers as the animal response especially of ruminants is not affected drastically after consuming the adulterated feed but the adulteration can be checked in laboratory by following methods:

(i)  Chemical analysis
(ii)  Bioassay assessment
(iii)  Feed microscopy

Chemical analysis: Proximate analysis of feed sample gives idea about the quality of raw materials or finished products. If the proximate composition of a product varies more than the specified limits, there is a possibility of adulteration. For example, lower protein and higher fibre content of an oil cake than its specifications indicate about the presence of some fibrous material such as hulls. Higher fibre and unaltered crude protein indicate that oil cake is adulterated with urea and/or some inferior quality oil cake, like mahua cake, castor cake, karanj cake, etc. The presence of these oil cakes may be visualized by their obnoxious flavour or specific taste. Moreover, these could be determined chemically. For example, development of violet or pink colour following the addition of few drops of concentrated sulphuric acid in the water extract of compound feed or raw oil cake indicate the presence of mahua cake. Presence of argimona seeds in mustard cake can be detected by adding few drops of concentrate nitric acid into the water extract of oil cake, which gives brown-reddish colour. Similarly, urea can be detected by adding few drops of DMAB reagent (2g dimethylamino benzaldehyde dissolved in 90 ml methyl alcohol + 10 ml HCl) in to the water extract of compound feed or any raw material. Any deepening of yellow colour indicates the presence of urea. Silica can also be estimated to judge the adulteration of feed with hulls. Some spot tests have also been developed to ensure the presence of minerals and drugs in the compound feed/ raw materials. Various chromatographic techniques may also be employed for the rapid detection of some incriminating factors, which evidently show the presence of undesirable feed ingredients.

Bioassay assessment: Along with chemical analysis or sometimes in place of it, bioassays are employed to detect the toxic materials. For example, fishes are extremely sensitive to the detergent properties of saponins, so that fish paralysis can be correlated with saponin content of the solution. But bioassay technique is less common for monitoring the quality of animal feeds.
 
Feed microscopy: Feed microscopy is commonly used for quality control of animal feed as well as confirming the adulteration and identifying the adulterants. Official procedures for basic feed microscopy are given by the Association of Official Analytical Chemists (AOAC). It needs very little sample preparation. A microscopist must be familiar with all types of feed ingredients and adulterants besides having a collection of

(a) pure feed ingredients

(b) adulterants

(c) contaminants.

These must be studied under low and high magnification for familiarization with their distinguishing features with coarsely or finely ground feed. Under low magnification (8 to 5O×) the materials examined are identified by the outwards physical characteristics like shape, colour, particle size, softness, texture etc. Under high magnification (100 to 500×) the plant cells and structural features of the material are taken into consideration, as these are not lost during grinding or even powdering