Last week we talked about the need for fish to eat. The plan is to formulate our own feed. A suggested nutrient content list was given but the now question is how to provide the required nutrition with the available feed stuffs. This is where Proximate Composition Analysis comes in.

Proxy what did you say? LOL.

Proximate Composition Analysis consists of a series of tests on a sample to determine its nutrient content.

Think of it like this… the sample, whatever it is, probably has water in it. So, if we weigh the sample and then gently heat it at 150 °F for some time, we can drive off the water. The material left over is known as Dry Matter (DM). The weight of DM subtracted from the original weight will tell us how much water it had. Simple, right? Now it gets a little more complex. The DM is made up of proteins, lipids, fiber, carbohydrates and ash.

Ash is easy to understand. It is the mineral residue left over after completely burning a sample. This is done by heating the sample at 550 °C for 6 hours in a muffle furnace. Again, it is an easy matter to calculate the percentage of ash in a given sample. This is usually expressed as a percent of DM.

There are some chemical tests that can be done to determine crude protein (Kjeldahl nitrogen x 6.25 if you want to get technical), crude lipids (commonly called Ether Extract or fat) and crude fiber content. But that doesn’t tell the whole story. There will be something left over. This is known as Nitrogen-free extract (NFE). Strange name because it has nothing to do with Nitrogen and is not an extract. It consists of carbohydrates, sugars, starches, and a major portion of materials classed as hemicellulose in feeds. When water, crude protein, fat, fiber, and ash are added and the sum is subtracted from 100 percent, the difference is NFE.

Well, there you have it. Proximate Composition Analysis in a nutshell. Uh, umm, maybe not. The proteins can be further broken down into the 20 constituent Amino Acids and the Mineral Content of the Ash can be determined. But you get the general idea. This is the way the contents of a feed stuff sample are analyzed.

Last thing… your mileage may vary. The results can be different for different samples due to species, stage of life cycle at harvest, the environmental conditions under which the samples were raised, etc.

So, with that, we will talk about published Proximate Compositions of various feed stuff species available to us on the Ranch in a post next week.