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Regulation of Feed Intake and Energy Balance

Regulation of Feed Intake and Energy Balance. Intake - Definitions. Fasting Zero intake Maximum intake Ad libitum “full feed” Allows for selection Orts = uneaten portion of meal Restricted intake Limited to consumption. Hunger and Appetite. Hunger Aroused by physiological need

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Regulation of Feed Intake and Energy Balance

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  1. Regulation of Feed Intake and Energy Balance

  2. Intake - Definitions • Fasting • Zero intake • Maximum intake • Ad libitum • “full feed” • Allows for selection • Orts = uneaten portion of meal • Restricted intake • Limited to consumption

  3. Hunger and Appetite • Hunger • Aroused by physiological need • Satisfied by calories • Appetite • Internal factors (physiological or psychological) that stimulate or inhibit hunger • Satiety • Lack of desire to eat • Controlled in hypothalamus

  4. Short Term Regulation of Feed Intake • Intake is usually measured on a daily basis, but daily intake is comprised of a number of separate meals, even when animals are fed ad libitum • Ruminants eat 10-15 "meals" per day • Some carnivores eat less than once daily • Should therefore focus on regulation of meal eating

  5. Feeding Initiation • The factors that start a meal are distinct from those that terminate a meal • Environmental factors can start a meal • Habit • Meal schedule dictates the intermeal interval • Can adjust meal size more easily than intermeal interval • Conditioned environmental cues (conditioned eating) – sounds from mixer wagon or feed cart • Stimuli in the environment • A clock (breakfast at 8 am, lunch at noon, dinner at 6 pm) • The sight/smell of food • Presence of others • Meal size goes up with group size

  6. Short-Term Hunger Signals • Glucoprivation is a decline in glucose available to cells  leads to hunger • Lipoprivation refers to a lack of fatty acids available to cells  leads to hunger

  7. Chemostatic Regulation • Monogastics • Glucose for short-term control • Ruminants • Little effect of blood glucose • Blood VFA may control • Hormonal control • Decreased leptin signals hunger • Increased cholestystokinin (CCK) signals satiety

  8. Regulation of Meal Eating • Feedback signals • Changes in regulated variables which lead to meal eating being switched on or off • Physical – distension (gut fill) • Chemical – VFA concentration, pH, osmolarity of digesta • Endocrine/neuroendocrine – numerous hormones (insulin, leptin, ghrelin) • Leptin produced by fat cells and suppresses long-term feed intake, stimulates metabolism • Cholecystokinin (CCK) regulates satiety during an individual meal

  9. Regulation of Meal Eating • Feedback signals • Many signals operate at the same time • Relative importance of different signals varies with diet (e.g., roughages vs concentrates), species (e.g., ruminant vs nonruminant) and physiological state (e.g., lactating vs nonlactating)

  10. Regulation of Meal Eating • Receptors • Chemoreceptors located in various splanchnic tissues detect VFA (rumen wall), glucose (liver) • Stretch or tension receptors located in gut wall detect gut fill

  11. Regulation of Meal Eating • CNS centers • Mainly in hypothalamus • Separate centers stimulate feeding (lateral hypothalamus) and satiety (ventromedial hypothalamus)

  12. Long Term Regulation of Feed Intake and Energy Balance • Changes the “set point” around which short term, homeostatic regulation occurs • The major factor driving these long-term shifts in intake regulation is energy demand • e.g., rat before, during and after lactation

  13. Feed Intake in Rat • Over 400% increase in feed intake during lactation • Dramatic reduction after lactation stops

  14. Regulation of Feed Intake and Energy Balance • Long-term regulation of energy balance is achieved by short-term regulation of meal-eating and feed intake • Energy balance, not feed intake, is the maintained variable in the homeostatic regulation of feed intake

  15. Summary for Monogastrics Most animals eat to meet their energy needs, unless bulkiness of the diet limits intake first

  16. Factors Affecting Feed Intake Caloric density and bulk density Caloric density: kcal DE/kg of diet wheat straw = 1,800 (beef) wheat grain = 3,920 (beef) animal fat = 8,130 (swine) Bulk density: weight per unit volume wheat = 60 lb/bu barley = 48 lb/bu oats = 32 lb/bu forages, ground = < 20 lb/bu High forage/fiber = bulky feeds

  17. Expected Forage Intake by Cattle

  18. Summary - Control of Feed Intake • Long-term • Wild animals do not overeat • Physiological state – lactation, estrus • Nitrogen and energy status • Environment – temperature, humidity, photoperiod • Short-term • Nerve impulses from GI tract, liver, brain • Humoral factors • Hormones – cortisol, insulin, estrogens, CCK • Metabolites – glucose, free fatty acids

  19. Inhibition of Intake • High protein • Heat increment with metabolism • High fat • Slow passage from stomach • CCK feedback on stomach motility • Caloric dilution • Poor quality feedstuff; limited feed allowance • Palatability • Salt

  20. Palatability • Palatability Preference when given a choice • Acceptability Amount consumed when not given a choice • Both determined by • Taste • Odor • Texture • Temperature • Visual cues

  21. Taste Preferences Cattle: sweet, sour Sheep: sour, salt Goats: all four, especially bitter Deer: sweet Horses: sweet, not sour Pigs: sweet, fat/oil Chickens: not sweet or sour Dogs: complex; fats, garlic Taste affects palatability more than acceptability

  22. Odor/Sight Odor strongly related to taste Visual cues have minimal effects except in humans

  23. Texture/Physical Form Particle size Processing methods Succulence

  24. Environment Season Temperature Availability of water Stress

  25. Stress and Feed Intake

  26. Body weight BW0.75 Individuality Behavioral or hormonal differences Production Growth, pregnancy, lactation Other factors Environment Stress Facility design Water consumption Predicting Intake

  27. Daily DM Consumed - % BW

  28. Strategies to Increase DMI (Ruminants) • Optimize rumen fermentation patterns • Avoid sudden ration changes • Feed more frequently • Leads to increased propionate production and increased digestibility • Increased microbial numbers and activity • Stimulate appetite • Keep fresh feed in front of cows • Exploit feeding behaviors • Feeding frequency • Free access to feed and water 24/7

  29. Feeding Behaviors (Ruminants) • Eat 10% of daily intake per feeding bout • Require 10 evenly spaced meals • 30 minutes per meal • Naturally spaced to allow fermentation, cud-chewing, and bulk elimination time • High intake vs. low intake ruminants • Amount of feed consumed per meal • NOT the number of meals • Total eating time about 5 hours • Requires feed access virtually 24 hours per day

  30. Feed Efficiency • High feed intake not always associated with high performance • High feed intake always associated with high feed costs • Feed efficiency defined as lbs meat or milk produced per lb of feed intake • Ranges from 1.3 to 1.7 for milk production • Cow producing 30,000 lbs. milk at 1.3 feed efficiency consumes 3 tons more feed than cow at 1.7

  31. Water Intake • Most ruminants drink 15 times per day • Fairly even intakes per drinking bout • Prefer warm water to cool water • Cold water significantly reduces intake • Water quality crucial

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