Chemical Analysis

What are the 4 things chemical analysis is used for?

1. Diet Formulation (improve accuracy of ration formulations to meet targeted requirements)

2. Economics (establish more accurate estimate of feeds economic value based on evaluated nutrients)

3. Commerce (ensure feed company’s are producing what they claim to be)

4. Environmental Impact (evaluating nutrients of animal outputs like manure)

What are some of the different chemical analysis that are used?

• Proximate Analysis System (chemical analysis)

• Van Soest analysis system (chemical analysis)

• Near Infrared Reflectance (NIR) Spectroscopy (non-destructive analysis)

What are the 6 fractions of the Proximate Analysis Systems?

• Water

• Crude Protein (CP)

• Ether Extract (EE)

• Ash

• Crude Fiber (CF)

• Nitrogen Free Extract (NFE)

How is water fraction obtained in the PAS?

Feed samples are heated at 105C for 24 hours

How is water content calculated in feed samples?

The difference in weight before and after drying

T/F The chemical assay in the PAS directly measures the concentration of protein

False, nitrogen concentration is measured

What assumptions are made about nitrogen concentrations in the PAS

Nitrogen content is only present in the protein fraction and the avg concentration of N is 16%

How is CP content measured in the PAS? Why?

N content x 6.25

Because of the assumptions made, the inverse of 16% is taken which is 6.25 and then multiplied by nitrogen content to estimate the CP content

What are the two different methods of measuring nitrogen contents in feed samples?

• Leco nitrogen analyzer

• Kjedahl nitrogen analyzer

Why would the CP assay not be accurate in PAS

• Not all protein contains 16% nitrogen (16% is just an avg)

• Nitrogen analysis does not distinguish between non-protein nitrogen (NPN) like urea and true protein

How is the ether extraction pulled from a feed sample in PAS?

Dry feed sample is extracted with petroleum ether, leaving behind the fat soluble components in the EE

What can be found in the Ether Extraction?

• True Fats

• Waxes

What decreases the accuracy of the EE fraction?

The difference between true fats and waxes is not distinguished in the assay which poses as a weakness because true fats are more digestible than waxes

How is the ash fraction obtained in the PAS?

Feed sample is combusted in a muffle furnace at 600C for 24 hours

Why is ash content important to know?

Besides denoting minerals (macro and minerals) it can also allow you to know how many contaminants are in the feed

T/F The Ash fraction in the PAS details the amount of specific macro and micro minerals

False

How is the Crude Fiber fraction extracted in the PAS?

The fat extracted sample is refluxed in a weak acid and a weak base, disrupting the cell wall to separate the cell wall from the cell contents. The cell wall contents are left behind including cellulose, lignin. and hemicellulose.

Why is the Crude fiber fraction not accurate in the PAS?

Some of the fiber content is solubilized with the cellular content including starch and proteins

How is the NFE obtained in the PAS?

It is not an actual chemical procedure, but a calculation

NFE (DM basis)= 100 - (CP + EE + CF + Ash)

What is the weakness in the NFE fraction of the PAS?

The calculations of the NFE contains the cumulative errors of other analysis

T/F NFE is highly digestible CHO

True

T/F The crude fiber fraction is not relied on in the PAS

True

What nutrients would you expect to find in Ash?

• Macrominerals

• Microminerals

What nutrients would you expect to find in Crude Protein?

• Protein

• Amino Acids

• Amines

• Non-protein nitrogen

• Nucleic acid

• Nitrates

• B-complex vitamins (contain N)

What nutrients would you expect to find in Crude Fat?

• Fats

• Oils

• Waxes

• Organic acids

• Pigments

• Fat-soluble vitamins

What nutrients would you expect to find in Crude Fiber?

• Cellulose

• Hemicellulose

• Lignin

What nutrients would you expect to find in NFE?

• Sugars

• Starch

• Pigments

• Fructans

• Pectin

• Some Cellulose

• Some Hemicellulose

• Some lignin

Why was the Van Soest System developed

It was developed as a more accurate system of analyzing CHO fraction of feedstuffs. Its system largely replaced the crude fiber analysis.

What two assays is the van soest system based on?

• Neutral detergent fiber assay

• Acid detergent fiber assay

What is the difference between NDF and ADF?

NDF contains cellulose, lignin, and hemicellulose while ADF only contains cellulose and lignin.

How do you calculate the cell contents (non-fiber components) in the VSAS?

Cell contents (DM basis) = 100 - NDF (DM basis)

Why is it important to be able to estimate the fiber content of feed samples?

Will help predict the digestibility of feed samples

What is the ADF-CP chemical assay?

It is used to measure heat-damaged protein as a result of excess heat from baling hay being too wet causing Maillard reactions

What is NIRS?

A method to rapidly and reproducibly measure the chemical components of feed samples with little or no sample preparation.

What is NIRS based on?

Based on chemical components having a unique infrared absorption spectrum that can be used to differ one chemical from another

What are the advantages of NIRS analysis?

• Analysis are carried out rapidly

• One operation can carry out multiple analysis

• Non-consumption of sample

• High precision (if database is good)

• Environmentally friendly

What are the disadvantages of NIRS analysis?

• Creation of databases of is expensive

• Instrument is expensive

• Dependent upon a good database

• Accuracy of NIRS is limited by availability and accuracy of databases

• Lack of sensitivity of analysis for minor nutrients