Feed Analysis

Hello :) As explained in the previous post, the composition of feed can be variable. Because of this, it is important to measure the nutritive values of a feed. How can we do this? This post will address this question by introducing you to the major chemical analyses of feeds used in animal nutrition. We'll take a look at proximate analysis and how it can be used to figure out Dry Matter, Crude Protein, Crude Fat, Crude Fibre, Ash and Nitrogen Free Extract that is in the food we give to animals.


Proximate Analysis 

This method of analysis separates the components of food into broad chemical groupings. The proximate analysis can be conducted using wet chemistry or NIR. 

Wet chemistry is more traditional and accurate, but can be time consuming and expensive. NIR is a faster and cheaper alternative but its accuracy relies on the technique and calibration used.

Proximate analysis separates feed contents into six groups: Moisture, Crude Protein (CP), Crude Fat, Crude Fibre, Ash, and Nitrogen Free Extract. 

This website has an excellent flow diagram that summarises the process that I will explain below. I recommend following this diagram as we go through the process in detail. 

Moisture

The original sample of food is either freeze dried or oven dried and the remainder of the sample is termed the moisture-free sample. This represents the amount of dry matter in the food. Thus the amount that evaporated represents the amount of moisture in the food. 

The formula to calculate dry matter (expressed as a percentage) is:

 DM = weight after drying / weight before drying X 100 

This information is used to express the content of the other nutrients on a "dry matter basis" (without moisture) or "as fed" (with moisture).

 Crude Protein

The nitrogen content of food is used to estimate the amount of protein present. There are two methods to measure nitrogen content: LECO and Kjeldahl. The LECO method is the most widely used method today. Crude protein relies on the fact that an average protein has approximately 16% nitrogen. Thus Crude Protein may underestimate or overestimate the true amount of protein present. It is also a poor indicator of protein quality. 

Crude protein is calculated as follows:

Crude Protein = N concentration X 6.25

 Crude Fat

Crude Fat (aka Ether Extract) represents the proportion of food that is soluble in a solvent. Thus in order the calculate this value, the sample is now placed in a solvent. The amount remaining after this step is used to calculate Crude Fat as shown below:

Crude Fat = Sample of food - fat free residue

 This amount is then divided by the amount of dry matter and the answer multiplied by 100 to calculate Crude Fat on a DM basis.

Ash

The sample is now boiled in acid and then boiled in alkali and then burnt in a furnace. The residue remaining after this is the Ash content of the food. It represents the inorganic component of the food, particularly minerals and may give an indication of diet quality. Diets high in ash are typically of lower quality or may be contaminated with other substances. This can be calculated on a dry matter basis as follows:

Ash (%) = Ash (in grams) / DM (g) X 100

Crude Fibre

This is the substance that remains after the sample is boiled in acid and alkali and burnt. 

Crude Fibre = % fat free residue - % ash 

 Crude fibre is the least accurately determined component as miscalculations earlier on in the process may be compounded during this step. The availability of this fibre for energy is also dependent on the type of fibre present and the ability of different species to digest fibre. 

Nitrogen Free Extract
 
Nitrogen free extract (NFE) is calculated by subtracting all the other components of the feed from the original sample of food. Ie:

NFE = 100% - (%Crude Protein + %Crude Fat + %Crude Fibre + %Ash + %Moisture) 

 NFE provides a reasonable indicator of the quantities of readily available carbohydrates, such as sugar and starch, in the food. It represents everything that we haven't yet measured in the proximate analysis.


That's it for now, if you have any questions please feel free to ask in the comments section below :)