Merits and Demerits of weende,s System of Feed Analysis

Overview

1. Introduction2. Proximate Principles3. Demerits of Proximate analysis4. Merits of Proximate analysis5. Conclusion

Introduction

Proximate principle

1.Water (moisture) 2.Crude protein3.Crude fat (ether extract)4.Crude fiber5.NFE (Nitrogen free extract) 6.Ash

Water (Moisture)Principle It is determined by drying feed sample in hot air oven at 100 0C for a specified length of time

• DM,% = wt after drying/wt before drying x 100%

• % Moisture = 100 – DM,%

•Moisture determines the keeping quality of hay•Moisture content determines the losses in silage making•Usefull in classification of feed in to succulent and non-succulent•Moisture content is significant in storage of feed•Moisture content is important while purchasing of feed•Moisture content is directly related to nutritive value of feed

Significance of moisture

Demerits • Drying above 60 oC can create artifacts

that hinder lignin, fiber & ADF analysis

• Most likely underestimate dry matter

• Loss of volatile fatty acids (VFA's)

Crude protein• Estimated indirectly by determining the nitrogen

content of feed and multiplying it with 6.25. • Estimated by a process developed by a Danish

chemist Johan Kjeldahl. • 100/16 = 6.25, therefore: NITROGEN x 6.25 =

CRUDE PROTEIN

Principle and ScopeIn the presence of sulfuric acid, sodium sulphate and a catalyst, the amino nitrogen of many organic materials is converted to ammonium sulphate. The ammonia is distilled from an alkaline medium and absorbed in standardized mineral acid.

Assumptions of Kjeldahl analysis1.All proteins contain 16% N. Hence uses constant‘6.25’ to convert N to protein.

2.All N in the food comes from true protein.

Problems with assumption 1

All amino acids are not created equal

Therefore, all proteins are not created equal

Amino Acid % Nitrogen Alanine 15.72 Arginine 32.16 Aspartate 10.52 Cystine 11.66 Glutamate 9.52

Protein % Nitrogen Casein 15.9 Glycinin 17.5 Hemoglobin 16.8 Ovalbumin 15.5 Serum globulin 16.2

(Kaiser et al., 1995) (Kaiser et al., 1995)

Problems with assumption 2

True protein in the plant is overestimated by the Crude Protein value (Maynard and Loosli, 1979).

• The use of concentrated sulfuric acid at high temperatures poses a considerable hazard

• The technique is time consuming to carry-out

 

Crude FiberPrinciple Two boiling processes simulate the pH conditions of the digestive tract

• Crude fiber composed of cellulose, hemicelluloses, and lignin

• Lignin is not a true carbohydrate

• The method has been widely used to determine the fiber content of feed but it has some serious shortcomings

Demerits

• C.F. - Indigestible and non nutritive residue

• Acid and base solubilize some of hemicelluloses, pectin and lignin

• NFE of a feed therefore tends to be overestimated

• Hence crude fiber underestimates true fiber

Crude fat Principle and ScopeA dried, ground sample is extracted with diethyl ether which dissolves fats, oils, pigments and other fat soluble substances.

Demerit • This process assumes all substances

soluble in ether are fats. Plant pigments, wax which are also soluble in ether, but do not have the same nutritional values of fats

Nitrogen free extract (NFE)Principle NFE represents the soluble carbohydrate of the feed, such as starch and sugar.% NFE = % DM - (% EE + % CP + % ash + % CF)

Demerit NFE not determined analytically but is calculated by difference. Therefore, NFE accumulates all of the errors that exists in other proximate analysis components.

Total Ash Principle When a sample is burnt in muffle furnace at 600oC for 2 hours, only mineral matter is left behind. This is the total ash or mineral content of feed. % Ash = wt. after ashing/sample wt. x 100%

Demerits • No indication of amounts of individual

minerals.• Long time required(12-24 hours).• Muffle Furnaces are quite costly to run• Loss of volatile minerals e.g., Cu, Fe, Pb,

Hg, Ni, Zn.

Advantages of Proximate Analysis• Comparison of feeds on a

specific basis• It is a common basis for the

feed purchasing and for ration formulation • No substitute till today except

for fiber component• It forms Starting point for

specific analysis•  Used for analysis of feeds,

faeces, urine, body tissues, body fluids

 

Conclusion• Proximate analysis is a system for

approximating the nutritive value of feedstuff without actually using it in feeding trial

• It is simple and yet descriptive method for evaluating the nutritive value of feeds

• Main demerits of this system are it underestimates dry matter, assumes that all proteins contain 16% N, crude fiber is considered as in indigestible non nutritive residue, this process assumes all substances soluble in ether are fats, it does not includes vitamins and gives no indication about kind of minerals present in Ash

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