1) Methods of Analysis for Nutrients and Feedstuffs

Question 1

What is chemical analysis?

Answer 1

A type of assay for measurement of feed components. Refers to traditional analyses performed in the lab, e.g. gravimetric, chromotographic, etc.

Question 2

What are the subdivisions of chemical analyses?

Answer 2

Empirical fractions: assays defined by the “fraction” or “extract” being measured, often a mixture of compounds. Usually gravimetric.

Specific analytes: measure specific, identifiable components. Usually chromotographic or spectoscopic.

Question 3

What is near infrared reflectance spectroscopy (NIRS)?

Answer 3

It is based on the correlation of NIR spectra with calibration made to chemical analysis data.

Question 4

What is proximate analysis?

Answer 4

Is a combination of analytical procedures for “crude” analyses of feeds. It has a limited value from a nutritional standpoint but is widely used.

Question 5

What are analyte-specific methods?

Answer 5

Used for measurement of specific nutrients. Limited application due to cost and applicability.

Question 6

What are the different components in which proximate analysis divides food?

Answer 6

1. Moisture
2. Crude protein
3. Crude fat
4. Crude fiber
5. Ash
6. Nitrogen-free extract

Question 7

Moisture procedure

Answer 7

Loss in weight that results from drying a known weight of food to constant weight at 105 degrees C. Results in dry matter (DM), and allows comparison of feeds with different moisture contents..

Question 8

Moisture procedure limitations

Answer 8

1) Volatile compounds, e.g. alcohols are lost at the temperature. This mainly a problem with fermented feeds.
2) Oven drying only measures physically-bound water (does not account for chemically bound water)
3) Drying at above 60 degrees C creates artifacts that hinder fiber analyses.

Question 9

What are other methods used to minimize loss of volatile compounds?

Answer 9

Vacuum drying, freeze drying, and distillation with toluene

Question 10

Crude protein (CP) method

Answer 10

Total N content is measured by Kjedahl or combustion method.

Question 11

What are the CP method assumptions?

Answer 11

1) All N in the food comes from true protein

2) The average protein contains 16% N

Question 12

Are the CP method assumptions correct?

Answer 12

No, because CP includes N from sources other than protein e.g. free AAs, amines, nucleic acid. However, non-protein N is only present in high amounts in a few seeds.

Question 13

Crude Fat/Ether Extract Procedure

Answer 13

Ground samples are extracted with diethyl ether. Solvent is evaporated and the residue is the ether extract

Question 14

What are the EE method assumptions?

Answer 14

That it represent high energy components, such as true fat and oil content

Question 15

Are the EE method assumptions true?

Answer 15

No, because complex lipids that are low in energy are also included (e.g. waxes, pigments, fat-soluble vits, sterols). It may also include proteins and other ether-soluble compounds that are not fat.

Question 16

Crude Fiber Procedure

Answer 16

Determined by using the ether extracted sample, boiling it in dilute acid, then dilute base, and the filtering and drying it in furnace. The difference in weight before and after burning is the crude fiber fraction.

Question 17

What is crude fiber?

Answer 17

Mostly made up primarily by plant structural CHOs, like cellulose and hemicellulose but also contains lignin.

Question 18

What are the limitations of the CF method?

Answer 18

The procedure is tedious and not highly repeatable. Also it is not an appropriate measure used to describe the nutritional value of feed.

Question 19

Ash Procedure

Answer 19

Ash is the residue remaining after organic material is burned off in a muffle furnace at 600 degrees C. It is composed of mineral elements and silica. Ash data is required to obtain other values, by difference.

Question 20

What do high values of ash indicate?

Answer 20

Contamination of samples with soil or inorganic materials.

Question 21

What is the organic matter (OM) of a sample?

Answer 21

It is calculated as the difference between its DM and ash content.

Question 22

What are the limitations of the ash method?

Answer 22

1) It excluded volatile minerals
2) It may include sand and other inorganic elements of organic origin
3) Little nutritional value

Question 23

What is the nitrogen-free extract (NFE) method?

Answer 23

NFE is calculated not measured, by the difference of original sample - (weight of moisture + CP + EE + CF + ash). It is composed primarily of soluble CHOs, including sugars, starches, fructans, pectins and organic acids.

Question 24

What is the limitation of the NFE method?

Answer 24

It is prone to large errors.