Quiz 15: Nutrients and Their Functions


Animal feeds are categorized as concentrates or roughages. Concentrates include cereal grains such as corn, wheat, barley, oats and milo, oil meals including soybean meal, linseed meal and cotton seed meal, molasses and dried milk products. Concentrates comprise of high energy and low and highly digestible fiber (80 to 90%). Roughages include legumes like alfalfa (pasture and hays), grasses and straws. Straw is the byproduct of production of grass, seed and grain. Roughage includes native and improved pastures as good source utilized by cattle, sheep, goats and horses. Additional roughages include silage, stovers like dried corn, cane or milo stalks and leaves with the grain part removed and soilage like cut green feeds. Roughages are less digestible than concentrates (50 to 65%) and the digestibility of some straws is even lower.

Terms like water and moisture are interchangeably used. Water is referred to the drinking water and moisture is referred to the amount of water given in feed or ration. The remainder of the feed without moisture is known as dry matter. Moisture occurs in all feeds ranging from 10% in air dry feeds to 80% in fresh green forage. A typical grass pasture may contain mix vegetation along with 25% dry matter approximately. Therefore, for every pound of vegetation consumed ¾ of pound is consumed as water. If a mature cow is assumed consume 25 pounds of green forage per day, the water intake from the feed source would be about 19 pounds (25lb x 0.75% moisture = 18.75lb) or 2.25 gallons.

Lipids comprise of fats and oils and are composed of carbon, hydrogen and oxygen. Lipids contain more carbon and hydrogen in proportion to oxygen than in carbohydrates. The fats are solids while are liquids at room temperature. Fats produce 2.25 times more energy per pound than carbohydrates. Lipids provide energy along with essential fatty acids. A triglyceride is a molecule containing three fatty acids bound to a glycerol molecule that serves as the back bone of the fatty acids. The fatty acids may be same or different and the attachment of the fatty acids to glycerol is a process known as esterification. The fatty acids have the basic structure containing long chains of carbon atoms linked together and are surrounded by hydrogen atoms. A carboxylic acid group (COOH) at one end of the chain in free fatty acids and a methyl group at the opposite end. The carbon chains mainly vary in number of the carbon atoms occurring in the chain, extent of the chain is saturated with hydrogen and the shape of the chain whether straight or bend. Fatty acids containing 12 or more carbons are called long chain fatty acids. Fatty acids with 6 - 10 carbons are called medium chained and with only 6 carbons are called short chain fatty acids. Fatty acids with no double bonds are called saturated. Fatty acids with one double bond are called mono unsaturated fatty acids. Fatty acids with 2 or more double bonds are called poly unsaturated fatty acids. Straight chained fatty acids are called Trans fatty acids whereas, unsaturated fatty acids with bent chains are called Cis fatty acids. The attachment of hydrogen to carbon chain of unsaturated fatty acids occurs by the process of hydrogenation. For livestock the dietary essential fatty acids required are linoleic acid and a-linolenic acid. The essential fatty acids serve two important functions such as precursors of prostaglandins and as structural components of cells. img

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