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Lecture 14

ANSC 2340 Lecture 14: Adipose Tissue

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Animal Science
ANSC 2340
Ira Mandell

1. Adipose Tissue Adipose Tissue:  Fat deposition o Result of tremendous inputs of feed energy o With steers, often trim away 6% BW during dressing and 6% BW during trimming  Changing role of carcass fat o 1800’s to early 1900’s-Fat was desirable: had very physical jobs, needed high consumption of energy o Today  Lowering Caloric requirements  Health concerns to decrease amount of fat consumed  Push towards Alternative fatty acid sources (plant based, unsaturated)  Fat removal  Want lean meat w/ superior eating quality Adipose Tissue: Functions  General classification: modified connective tissue (CT)  Energy store o Energy content in fat vs CHO and protein? Has 2.25X the energy  Thermal insulator o Prevents heat loss  Mechanical shock absorber  Improves appearance of a finished carcass o Use of the term “finishing” in red meat production  Improves palatability Role of Adipose Tissue  Carcass quality o Finished appearance o Effect on grading? (Beef and pork)  beef: fat cover & marbling for quality  both: fat cover affects $ to producers  Marbling fat  Tenderness: what do scientific studies show with beef? Not that important  Important for Juiciness  Important for Flavor intensity  Off flavors: what you feed the animal may change fatty acid composition of fat, may cause an undesirable eating experiences Adipose Tissue: Where is it located?  Beneath the skin o Name of this fat depot = subcutaneous  Between muscles o Name of this fat depot = intermuscular  Behind the eyeballs  On the surface of the heart + around kidneys  Surrounding joints  In bone marrow  Among the omentum of the abdomen (belly fat) o An example of internal, visceral, body cavity fat  Within the muscle o Name of this fat depot = intramuscular Development of the adipocyte and where it’s derived from: notice in the developing adipocyte how the volume of nucleus, cytoplasm, and organelles shrink as the cell fills up with triglyceride Adipose Tissue: Origin  Fetal synthesis o Role of mesenchyme: originates from mesoderm (synthesizes connective tissues)  Mesoderm is one of the 3 primary germ lines that will produce all the tissues in the body  Others are ectoderm and endoderm  Synthesis of blood, skeletal tissues, lymphatic cells, connective tissues (including adipose tissue)  quite diverse tissues derived from same germ line  Adipose cell precursors congregate in globules  Accumulates small droplets of lipid  Droplets will congregate and form large mass of lipid in the center of the cell o High muscle breeds can’t produce much CT or adipose tissue  Role of adipose cell precursors called preadipocytes or adipoblast o These cells resemble?  In theory, same cells that produce collagen and elastin can produce adipose tissue  Piedmontese cattle: low numbers of mesenchymal cells o do not produce much collagen or adipose tissue: tender beef w/o fat o Located wherever fat may develop o Stimulated to differentiate by various hormones (don’t worry about hormonal control)  Insulin, thyroid hormones, IGF-1 Adipose Cell Characteristics:  Adipocyte: name of cell filled with lipid o Has nucleus, mitochondrion, organelles, cytoplasm pushed to one side of cell o Only small amounts of cytoplasm  Results in low water content (high dry matter [DM])  20 g fat comes with 1 g water (< 5%)  In 100 g of muscle, 20 g meat protein comes with 80 g water (80%)  Finishing red meat species; requires more feed per unit gain than with growing diets o putting on fat rather than lean; more DM with fat o Mature cells: > 95% lipid or triglyceride  Once starts to store triglyceride, no longer can divide  Notice how in the developing adipocyte, the volume of the nucleus, cytoplasm, and organelles shrink as the cell fills up with triglycerides (TAG’s)  Muscle = high in water content  Fat = low in water content o REFER TO IMAGE ON PAGE 2  Squished cytoplasm, etc  Feeding farm animals: o May be fed a starter diet (pigs, poultry) and then a growing diet followed by a finishing diet o Starter diet: very concentrated in nutrients including protein. Animals are very immature thus have high nutrient requirements. Animals are very efficient at converting feed to grain, these animals don’t eat much (why high concentrated is needed) o Growing diet: less concentrated in nutrients. Still efficient at converting feed to grain as they grow muscle and structure. o Finishing diet: least concentrated in nutrients except for energy while seeing the greatest feed intakes. No longer efficient at converting feed to gain, instead are putting down fat which is high in DM. Adipose Tissue Depots:  Definition: areas or locations in the body where there is accumulation of adipocytes  Range in size o Small groups of cells between muscle fasiculi called intermuscular or seam fat  Not much value to the meat industry o Large numbers of cells subcutaneously or viscerally o Intramuscular fat deposited in loose networks of perimysial connective tissue close to blood vessels  Well supplied by blood capillaries (highly vascularized) o Why? Needed to create adipose depots to begin with, needed if the animal needs to mobilize fat stores as a source of energy  Dynamic nature of Adipose tissue o Continuously grows in animals depending on energy intakes versus energy requirements  Hypertrophy (increased size) of the adipocytes occurs when?  Energy intake exceeds energy requirements/expenditures (dealt with as we get older) o Can be mobilized depending on nutritional status of the animal  Fat cells can be used by the animal for energy supply  Net fat accretion dependent on?  Accretion means the process of growth or enlargement by a gradual buildup o Above requires rich supply of blood vessels and enzyme systems  Internal, body cavity, visceral fat o Protects + insulates organs o Omentum (or caul fat)  Thin connective tissue sack filled with fat  Located over stomach and intestines o Mesenteries (or lace fat)  Thin CT membranes supporting intestines  Internal, body cavity, visceral fat o Kidney or renal fat  Knob of hard fat around the kidneys  Used as suet fat: to make dough  Brittle fat at room temperature as has high melting point due to its location as compared to SQ (subcutaneous) fat which has low melting point  How does location fit in? kidney fat located in the core of the body where there is a warmer temp than subcutaneous fat (difference in fa composition results in different characteristics) o Omentum, mesenteries, and kidney fat make up 30% of the fat in a steer o Kidney fat removed during dressing of beef carcass but remains in pork carcass Lambs? Kidneys are left in the carcass Phases of Fat Deposition:  Phase 1: Internal fat is the first fat depots to be deposited in the body o Visceral and kidney fat o Caul fat (omentum) and mesenteries  Phase 2: o Subcutaneous o Intermuscular  Phase 3: o Intramuscular (IMF)  Any thoughts on why fat deposition occurs this way? Put down the fats most critical for survival and function first Fat Deposition:  Back-fat in pigs o 3 layers  Outermost layer  First to develop  Acts as insulation  Middle layer  2 layer to form  Thickest of the 3 layers  Most metabolically active  Inner layer  Last layer to form  Intramuscular fat  Deposited between individual muscle fiber bundles  Associated with perimysium (CT) Factors Affecting Fat Deposition:  Breed differences in fattening o Early maturing cattle deposit fat at an early chronological age than late maturing cattle  Early maturing cattle are physiologically older  Early maturing cattle (British breeds)  Late maturing cattle (Continental breeds)  Breed differences attaining  Height  Body composition (continental = leaner, less fat)  Onset of puberty (British calf earlier) o Can select against fatness (target back-fat)  Sex differences o Steers and weathers = leaner than heifers and ewe lambs o Gilts are leaner than barrows (an exception)  Boars are leaner than gilts o Leaner carcass with intact males (bulls, boars, rams) than castrated males (steers, barrows, weathers) o Body weight at fattening (attaining identical back-fats)  Rank bulls, steers, heifers  Which gender will have the lightest BW at fattening? heifers! Heifers fatten first, bulls are the leanest  Which gender will have the heaviest BW at fattening? bull Controlling Fat Deposition:  Cellular hyperplasia: increased cell numbers  Cellular hypertrophy: increased cell size  Ho #1: Adipose cell numbers are genetically regulated o Select for low numbers (hypoplasia) to increase lean meat deposition and reduce carcass fatness  Ho #2: Adipose cell numbers are nutritionally regulated o Feed low energy diets early in life and that will reduce fat deposition later in life  Want to grow muscle and bone early in life: growing rations: we do this now in production  Want to fatten or finish later in life: finishing rations: we do this now in animal production  Ho #1: Select for low numbers to increase lean meat deposition o Doesn’t work  Adipose cells can be formed from precursor cells (mesenchyme cells) that are similar to fibroblasts  Ho #2: Adipose cell numbers are nutritionally regulated o Doesn’t work as can recruit extra adipose cells to enable compensatory growth  Where are these cells recruited from? fibroblast like cells  Genetic control o Double muscle cattle  Cellular hypoplasia for adipose cells (reduced # of AT cells) o Mice  Can alter adipose cell number and size (either way) o Pigs in the 50’s and 60’s versus pigs today  50 years ago: pigs with 50 mm back fat  Today: pigs with as little as 17 mm back fat  Have been able to drop back fat by 2/3!! o Commercial selection for decreased back fat thickness  Decreases total carcass fat  Less adipocyte hypertrophy  Less recruitment of new adipocytes Fat Deposition and Palatability:  Marbling or IMF fat associated with increased tenderness o In the good old days, farm animals eaten when their days producing milk or as draught animals were over o Ho: IMF melts away from bundles of muscle fiber to enhance tenderness  Not backed up scientifically o IMF may act as a lubricant in mastication of less tender meat; increased perception of juiciness will increase assessment of tenderness o Enhanced tenderness in roasted poultry that are basted in melted subcutaneous and intermuscular fats Fat Deposition and Juiciness:  Juiciness important for overall palatability of the meat o Limited juiciness, dry product will impact the perception of tenderness and flavor  Juiciness attributed to IMF and water in meat o Melted lipids make up a broth that are released upon chewing o Melted fat translocated along perimysial CT which limits moisture loss  Minimize drying and shrinkage during cooking  Meat flavor o Carbonyl compounds in adipose tissue  Presence of specific fatty acids impacts meat flavor you can ensure superior eating quality between 3-7.3% IMF Ether extractable lipid = intermuscular fat White adipose: cytoplasm and organelles squished to one side Brown adipose: smaller in size, doesn’t have a large fat globule (triglyceride) Brown Fat:  Found in newborns (including farm animals), cold adapted animals, + hibernating mammals o None to few in piglets (disagreements on this) o None in poultry o Important for temperature regulation as acts as a site for heat production  Important for some newborn animals so they can produce heat during vulnerable periods such as right after birth and during winter  Piglets are born with very little fat period  vulnerable to being chilled; can be a major cause of death o Talking about warming the animal opposed to mobilizing the fat for energy production in white adipose  Differs from white fat cells o Smaller in size o More mitochondrion  Color of mitochondria responsible for calling it brown fat o High content of cytochromes means aerobic metabolism o Triglyceride found as small droplets  How does this differ from white fat?  Much smaller fat droplets opposed to one large fat globule o Oxygen consumption o More vascular than white fat  To distribute heat produced from lipid oxidation + electron transport reactions o Abundant cytoplasm: small droplets of fat vs large globule of fat in white AT  Disappears shortly after birth (different theories as to why) o Depleted – Gets used up by the animal o Converted to white AT (adipose tissue)?  Some sources question if farm animals have brown AT; if they do, doesn’t last long as converted to white AT  Heat generation by n
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