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NUTRIENT REQUIREMENTS AND FEED VALUES


COLLECTION: GOAT HANDBOOK
ORIGIN: United States
DATE INCLUDED: June 1992

Extension Goat Handbook

This material was contributed from collections at the National Agricultural Library. However, users should direct all inquires about the contents to authors or originating agencies.

DOCN 000000022
NO C-1
NUTRIENT REQUIREMENTS AND FEED VALUES
R. S. Adams; Pennsylvania State U., University Park B. Harris; U. of Florida, Gainesville M. F. Hutjens; U. of Illinois, Urbana E. T. Oleskie F. A. Wright; Rutgers U., New Brunswick, NJ
D. L. Ace; Pennsylvania State U., University Park
Nutrition


1 The Ruminant Stomach The dairy goat belongs to the cud-chewing or ruminant group of animals. This group, which includes cows, sheep, and deer, has the unique ability of being able to digest roughages which contain relatively large amounts of cellulose. Cellulose is a part of plants and thus one of the largest potential sources of energy for animals. The digestive system of ruminants can also manufacture many essential nutrients. Drawings of the four compartmentalized stomachs of the ruminant are shown in Figure 1, indicating the changes from youth to maturity.

2 Rumen -- This is the largest of the four compartments representing about 80 percent of the total stomach area. The rumen is often called a fermentation vat because it contains a large number of microorganisms bacteria and protozoa, which supply enzymes that break down fiber and other parts of the feed. The cellulose is converted to volatile fatty acids that are absorbed through the rumen wall and provide up to 75 percent of the total energy needs of the animal. Protein is produced by the microorganisms from the nitrogen in the feed. The microorganisms also manufacture all the B vitamins along with Vitamin K.

3 A unique feature of the rumen is that it is located in the beginning of the digestive system. This position makes it possible for the host animal to take advantage of all the nutrients produced by the microorganisms as well as the organisms themselves further on down in the digestive tract.

4 Reticulum -- This is the second stomach, sometimes called the ''honeycomb'' due to the structure of its wall and is located just below the entrance of the esophagus into the stomach. Act ually the reticulum is a part of the rumen, separated only by a partial wall.

5 Omasum -- This portion of the stomach is shaped like a small cabbage. It consists of hanging layers of tissue similar to the curtains on a stage. The relatively large surface area of these folds permits absorption of moisture from the feed as it passes through to the fourth compartment.

6 Abomasum -- This part is more often considered the true stomach. It functions just like that of the simple-stomached animals. It contains hydrochloric acid and enzymes that break down feed materials into simple compounds that can be absorbed by the stomach wall and the intestines.

7 Food from the mouth passes through the esophagus and enters the rumen, where it is mixed with ruminal contents and fermented and degraded by ruminal microorganisms. Some of the feed is regurgitated for more mastication (chewing the cud) and then returned to the rumen for additional fermentation. Fatty acids resulting from fermentation of the feed are absorbed into the blood stream from the rumen and reticulum. The remainder of the feed passes through the omasum and abomasum where further digestive action takes place. As feed ingesta enter the small intestine, enzymes further break it down and the released nutrients are absorbed into the blood stream for use by the goat. The ruminant animal is unique in that fibrous feeds can be utilized with the help of ruminal microorganisms. Also, all amino acids can be synthesized by the microorganisms from plant proteins as well as all the required B-vitamins and vitamin K.

8 Primary Feed Nutrients Generally, feed nutrients are divided into six groups. Following is a brief discussion of these nutrients:

9 Protein -- Protein is the only nutrient that contains nitrogen. Protein quality - a term referring to the amino acid content - has no significance in ruminant nutrition, except at exceptionally high levels of milk production. Rumen microorganisms manufacture their own body protein, consisting of all the necessary amino acids, which are later digested by the host animal.

10 Protein makes up the basic animal tissue of the body and is vital for growth, milk production, disease resistance, reproduction, and general maintenance. The body has very little if any excess protein. Mostly, the nitrogen is eliminated by the kidneys and the rest is burned as energy. Since protein is generally the most expensive part of the ration, it is costly to feed more than what is needed. Protein requirements vary between 12 and 16 percent of the ration dry matter with the latter needed for high milk production.

11 Urea and other nonprotein nitrogen products can be utilized by the microorganisms of the rumen for the production of protein. They are not generally recommended for goats because they are very selective in their diets.

12 Energy -- One of the first limiting factors of milk production is a shortage of energy. This short age is most likely to occur at the very early stages of lactation. Most of the goat's energy comes from the breakdown of the fiber of forages, while the remainder comes from the burning up of concentrate starches and fats.

13 Energy is measured in two different ways by the feed industry. The first and more established method is by Total Digestible Nutrients (TDN). As the name suggests, the TDN consists of the sum of the digestible carbohydrates, digestible protein, and digestible fats (multiplied by 2.25 since fats contain that much more energy than protein or carbohydrates). The TDN system takes into consideration only one nutrient loss - feces. For this reason, the net energy system is gaining in popularity. This system considers energy that is lost in the feces, urine, gases, and the work of digestion. In recent years this system has been even more refined to account for varying energy utilization needs for body maintenance, weight gain, or milk production.

14 Minerals -- Many minerals are required by the goat. Most can be obtained from good forage and a regular concentrate mixture. The major minerals of concern are calcium, phosphorus, and salt, which are usually added to the ration either in the grain mix or by free-choice feeding. Goats do not consume minerals free choice according to their needs. It is, therefore, recommended that minerals be force-fed through the grain mixture or mixed with a succulent feed like silage or greenchop, if possible. The ratio of calcium to phosphorus is important and should be kept around 2:1. If these minerals must be fed free-choice, such as to dry goats and yearlings, a good mixture is one containing equal parts of salt and dicalcium phosphate, or a similar commercial mix.

15 Vitamins -- Vitamins are needed by the body in small amounts. Since all the B vitamins and vitamin K are produced in the rumen and vitamin C is manufactured in the body tissues, the only vitamins of concern in ruminant nutrition are vitamins A, D, and E. During the late spring, summer, and early fall the animals can get all they need from green pastures and plenty of sunshine. In addition, they can store a good supply of these vitamins to carry them into the winter months. Nevertheless, it is a good idea to add these vitamins at the rate of 6 million units of vitamin A and 3 million units of vitamin D to each ton of grain mix during the winter months as an added precaution since they are not very expensive.

16 Fats -- Fats are of little importance in the ruminant ration. Practically all feeds contain small amounts of fat, and added levels are not practical. A level of 1.5 - 2.5 percent in the grain mixture is normal.

17 Water -- This is the least expensive feed ingredient, yet a deficiency will affect milk production more quickly than the lack of any other nutrient. Water is not only the largest single constituent of nearly all living plant and animal tissue, but it also performs exceedingly important functions during digestion, assimilation of nutrients, excretion of waste products, control of body temperature, and the production of milk. Ready access to water is important. Goats with water constantly available have been shown to produce more milk than those watered twice daily and over 10 percent more than those watered only once per day.

NUTRIENT REQUIREMENTS AND FEED VALUES
COLLECTION;GOAT HANDBOOK
ORIGIN;United States
DATE_INCLUDED;June 1992


 
 


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