Understanding Lipids and Fats

• Lipids are organic compounds found in plants and animals.
• They include substances extractable from biological materials with fat solvents like benzene, ether, chloroform, carbon tetrachloride, and acetone.
• Lipids are insoluble in water but soluble in organic solvents.

Lipid Classification

• Lipids can be classified as saponifiable (simple and compound) and non-saponifiable.
• Simple lipids include fats & oils and waxes.
• Compound lipids include phospholipids, sphingolipids, glycolipids, and lipoproteins.
• Non-saponifiable lipids include steroids, prostaglandins, fat-soluble vitamins, and trepenes.

Types of Fat

• Unsaturated fats are considered "good" fats that help lower blood cholesterol.
• Sources of unsaturated fats include fish, nuts, seeds, plant oils, avocados, olives, walnuts, and liquid vegetable oils.
• Saturated fats are considered "bad" fats that raise cholesterol levels.
• Sources of saturated fats include beef, beef fat, veal, lamb, pork, lard, poultry fat, butter, cream, milk, and cheese.
• Trans fats are considered "very bad" fats that raise cholesterol and increase the risk of heart disease.
• Sources of trans fats include vegetable shortenings, some margarines, crackers, cookies, and snack foods.

Fats and Oils

• Fats are solid at room temperature (25°C), while oils are liquid at the same temperature.
• Lipids from animal sources are usually solids, while oils are generally of plant origin.
• In animal nutrition, both fats and oils are referred to as fats.
• They are composed of fatty acids and one molecule of glycerol, forming mono-, di-, or triglycerides.
• Fatty acids consist of chains of carbon (C) atoms, ranging from 2-24 or more in length, with a carboxyl group on the end.
• Saturated fatty acids have all available positions on carbon atoms taken up with hydrogen.
• Unsaturated fatty acids have one or more double bonds.
• Fats contain the elements carbon (C), hydrogen (H), and oxygen (O), but are relatively much higher in C and H.
• Fat: 77% Carbon,12% Hydrogen, 11% Oxygen
• Starch: 44% Carbon, 6% Hydrogen, 50% Oxygen
• 1 gram of typical fat yields about 9.45 Kcal of heat when completely combusted.
• 1 gram of typical carbohydrate yields about 4.15 Kcal.
• Oils in plant seeds are generally triglycerides.
• Lipids in forages are mostly diglycerides with a galactose molecule attached to glycerol, called galactolipids.
• Branched-chain FAs and those with an odd number of carbon atoms are often produced by microorganisms.
• Ruminant animal body fats can contain substantial amounts of these FAs.

Examples of Saturated Fatty Acids

• Acetic (C2:0)
• Propionic (C3:0)
• Butyric (C4:0)
• Caproic (C6:0)
• Myristic (C14:0)
• Palmitic (C16:0)
• Stearic (C18:0)
• Arachidic (C20:0)
• Lignoceric (C24:0)
• "C 2" means that it contains two C atoms & "0" means that no double bonds are present

Examples of Unsaturated Fatty Acids

• Palmitoleic (C16:1)
• Oleic (C18:1)
• Linoleic (C18:2)
• Linolenic (C18:3)
• Arachidonic (C20:4)

Practical Diets

• Practical diet for farm animals contains fats for transport and absorption of fat-soluble vitamins.
• Fats act as sources of essential fatty acids.
• They help to increase energy concentration of the diets.
• Examples of fats used include tallow, soybean oil, and byproducts of edible oil refining.
• Poultry fat supplementation is at 5-10%.
• Adult ruminant fat supplementation is at 3-5% ("more in dairy cattle, 6-8%").
• Non-ruminant fat supplementation is at 10-15%.
• Too much fat in ration will lead to reduced feed intake, increased chances of scouring, and insoluble calcium and magnesium.
• Young animals receiving a high level of milk in diet will be getting 25-40% fat "on DM basis".
• Ruminants on dry feed are less tolerant of high fat level than are monogastrics "not more than 6-8%".
• Adverse effects of high lipid intake "above 10%" in ruminants include reduction of the rumen microbes activities and fermentation of carbohydrates.
• High lipid intake can be overcome by feeding "protected fats".

Protected Fats

• Protecting fats involves encapsulating small droplets of oils in a thin layer of formaldehyde-treated protein (casein).
• The droplets avoid attack by microorganisms during passage through the rumen.
• The fat is released by the acidity of the abomasum and thus becomes available for digestion and absorption from the small intestine, as in non-ruminants.
• Rumen-active oil kills rumen bacteria, reduces fiber digestion, and produces trans fatty acids, leading to milk fat depression.

Types of Rumen-Protected Fat Supplements

• Saturated fatty acids

• Calcium salts of palm oil

• Feeding unsaturated fat in protected form results in rise in the degree of unsaturation of plasma lipids, milk and body fat.

• Unsaturated form has been promoted in the context of prevention of human heart diseases and atherosclerosis

• The connection between human diseases and intake of saturated fat is controversial, the shelf-life of unsaturated milk is poor.

Omega-3 and Omega-6 Fatty Acids

• Fish oils have a protective effect against atherogenic process in humans due to their high content of polyunsaturated FAs
• Linolenic acid (C18:3)
• Ecosapentaenoic acid (EPA, C20:5)
• Docosahexaenoic acid (DHA, C22:6)
• Marine fish have a higher content of omega-3 FAs than fresh water fish.
• Content varies with species, season, water temperature, and the food eaten by the fish.
• Omega-3 FAs lower total serum lipids and cholesterol and also modulate the conversion of arachidonic acid to prostaglandins and other compounds.
• Feeding laying hens these ingredients produce omega-3 FAs-enriched eggs.
• Omega-3 products can be increased by the use of fish meal or full-fat linseed
• Linseed is one of the richest plant source of omega-3 FAs, such as linolenic acid.
• These products are acceptable in taste to consumers and may have value in healthful diets for avoiding coronary heart diseases.
• Omega-3 FAs are dietary essential for fish.
• Its deficiency leads to poor growth, liver and heart lesions, and a shock syndrome.
• For dogs, omega-3 and omega-6 FAs are essential fatty acids that prevent and treat dermatitis.

Digestion and Absorption of Fats

• Fat digestion and absorption differ principally from that for carbohydrates or protein, since fats are non-polar and not miscible with water.
• The primary object of lipid digestion is to arrange the lipid in a water-miscible form for absorption through the microvilli of the small intestine.
• In simple-stomached animals, the site is the small intestine.
• Digestion is emulsified by bile which emulsifies the fat (oil-in-water emulsion).
• Increasing surface area is aided by bile.
• Pancreatic lipase hydrolyzes FAs from the glycerol molecule.
• Gastric lipase activity is low.
• Most absorption occurs as monoglycerides and fatty acids.
• The majority of the longer chain FAs are absorbed by lacteals into the lymph system and enter the blood stream just before the vena cava vein enters the heart.
• In ruminants, galactose is fermented to volatile FAs, which are absorbed through the rumen walls.
• Lipids are largely hydrogenated (saturated).
• Does not primarily result in monoglycerides, but yields glycerol and free FAs.
• Bacteria and protozoa (rumen microbes) synthesize FAs for the lipids of their own cells.
• Microbes include acids with branched chains and odd numbers such as 13, 15 and 17 carbons.
• The 15-carbon acids are predominating.
• Microbial cells pass from rumen through omasum to the abomasum.
• Bacteria and protozoa disintegrate, releasing their lipids.
• All these products pass to the small intestine, where any triglyceride is hydrolyzed by pancreatic lipase to monoglyceride and FAs, as in nonruminant.
• They are absorbed in the same manner as in nonruminants.
• In the intestinal mucosa, resynthesis of triglycerides and phospholipids occurs.