Food or feed is the source of materials that an animal's body needs to grow or to replace what it is using each day. In order to gain some information about what is in a feed or an ingredient, a procedure is followed that separates all feeds into six different parts or fractions. These are moisture or water, crude protein, crude fat, crude fiber, ash or mineral, and nitrogen-free extract. Results of some of these analyses are found on feed tags or food labels. All of these fractions are determined by using relatively simple chemical procedures. Information gained from these procedures is called the proximate analysis.
All feeds contain some moisture. The usual amount is from 8 to 10%. If the percentage of moisture is too high, feeds will spoil by getting moldy. This happens if feeds have approximately 15% or more moisture. Animals can use moisture from the feed as a source of water for their body, which is about two-thirds water. If animals are on pasture, the fresh plants that they eat will have a much higher water content, as much as 80 or 90%. In order for the animals to meet their needs for water, they must have a source of clean water. Animals that don't get enough water will become dehydrated. This will affect their health and may cause death in extreme conditions.
Waterfowl eat foods or feeds that contain a high percentage of carbohydrates. Two fractions of the proximate analysis, nitrogen-free extract (NFE) and crude fiber, give information about carbohydrates. Most of the NFE in feed ingredients is starch, but sugars are also part of this fraction. Manufactured duck feeds have most of their carbohydrates as NFE and only a small proportion as fiber. Cereal grains make up a large proportion of a complete feed, and grains are high in NFE. Flour is an
example of an ingredient that is very high in NFE because other fractions of the proximate analysis were removed while making it. The average composition of feed ingredients can be found in the National Research Council publication for poultry. Waterfowl can digest most of the NFE in feeds, but little of the fiber can be digested. If waterfowl are eating whole plants while on pasture, their diet will contain more fiber than they would usually get with complete feeds. Alfalfa meal is more similar to pasture plants than to cereal grains.
Digested carbohydrates are the main fuel source for the body. Glucose (sugar) is the main carbohydrate that results from digestion. The use of glucose for fuel might be compared to a fire that is burning wood. The fire consumes wood and gives off heat. In a related way, an animal's body consumes glucose and gives off heat. The way an animal's body uses fuel does not release heat as quickly or it would destroy itself, but the fact that birds maintain a body temperature of approximately 41 °C is evidence of heat production.
Fat that is in feeds can also be digested and used for energy. Most feeds contain less than 4% fat. If ingredients are used that increase the dietary fat by several percent, waterfowl can digest the additional fat.
Protein in feeds is digested to amino acids. Growing birds use the amino acids to make muscle and other body proteins. Females laying eggs use amino acids to make protein that is in the egg. Mature males also need some amino acids to replace protein in their body that is used during maintenance and for some specialized functions. As a result, waterfowl that are making a lot of their own protein need slightly more protein in their feed than waterfowl that are not making as much protein.
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