Bioenergetics PDF

Bioenergetics Prepared on 131024 by DBM, AP I, DBVS, for Zootechnics 113 Lecture, 1st Semester, AY 2024 - 2025 Objectives  To introduce different energy terminology and discuss energy flow through an animal  To discuss the measurement of energy...

Bioenergetics Prepared on 131024 by DBM, AP I, DBVS, for Zootechnics 113 Lecture, 1st Semester, AY 2024 - 2025 Objectives  To introduce different energy terminology and discuss energy flow through an animal  To discuss the measurement of energy retention and disorders related to energy metabolism in livestock New Terms  Calorimetry  Comparative slaughter technique  Digestible energy  Energy  Gross energy  Heat increment  Ketosis  Metabolizable energy  Net energy  Obesity  Total digestible nutrients Why Study Bioenergetics in Animal Nutrition?  energy metabolism in the animal body and the movement of energy from one form to another.  units of measurements, distribution of energy in the whole animal, and disorders related to energy metabolism. Why Study Bioenergetics in Animal Nutrition?  Bioenergetics is the study of the balance between energy intake and utilization by the animal for different life-sustaining processes: 1. osmoregulation, 2. digestion, 3. locomotion, 4. tissue synthesis  Energy intake in the animal is through feed and energy losses are through different sources such as heat, feces, urine, and other gaseous losses. Units of expressing energy  Calories used in the US (One calorie is the amount of heat required to raise the temperature of one gram of water by 1° C from 15.5° C to 16.5° C.).  In other countries and in scientific journals, joule is used. (One thousand (1,000) calorie is one kilocalorie (1 kcal) and 1 kcal is 4.184 joules (J)).  For practical purposes, kcal is commonly used in ration formulation and in expressing caloric value of feeds. Energy Terms  Gross energy  Digestible energy  Metabolizable energy  Net energy  Different energy measurements and flows of energy in the animal *This is negligible in monogastric animals. What is the clinical significance of soil contaminating food? Energy Measurements: Gross Energy  the total amount of chemical energy in the diet consumed (aka heat of combustion)  GE content of feed is measured as heat liberated during complete burning (oxidation) of the feed sample and is determined by an apparatus called a bomb calorimeter.  it does not provide much information on the nutritional value of the feed and does not account for palatability, digestibility, or other animal physiological factors.  High-protein and high-fat feeds will have more energy than high carbohydrate feeds, and feeds with high ash will have less energy than lower ash feeds. Energy Measurements: Digestible energy (DE)  the energy remaining in the diet after fecal energy is subtracted.  DE represents the indigestible components of the feed that will be excreted in the feces; however; they still contain energy that was not utilized by the animal.  Fecal loss of energy is the major source of energy loss to the animal  DE is calculated as Gross Energy (GE) − fecal energy (FE) Energy measurements: Metabolizable Energy (ME)  the energy remaining after urinary loss and gaseous losses arising from the gastrointestinal tract are subtracted from DE.  Values obtained reflect losses due to digestion, fermentation, and metabolism of the feed by the animal.  Urinary loss is the major one and is the total energy lost in urine.  Urinary losses are usually stable but can increase when high protein is included in the diet. Energy measurements: Metabolizable Energy (ME) continued…  Gaseous products of digestion include combustible gases produced by the digestive tract during fermentation of food by microbes (methane, carbon monoxide, hydrogen).  In ruminant, 4% to 8% of feed energy is lost from the rumen as methane.  Losses from gaseous loss are minor and are ignored in monogastric species.  On average, combined energy losses in gases and urine are about 18% of DE in ruminant animals.  To determine metabolizable energy, metabolic trials are conducted using live animals. Daily intake (feed) and losses (fecal, urinary, gaseous) of energy are documented. Breathing masks (or chambers) are used to assess gaseous losses.  ME can be used for two purposes: (a) maintenance and (b) production. Net Energy  Net energy (NE) is ME minus the heat generated by the inefficiency of transforming energy from one form to another.  Simply speaking, heat generated is heat lost during the energy transformation process and is called the heat increment (HI).  No matter what purpose ME is used for, this is not at 100% efficiency. This inefficiency of the biological system is represented by HI.  Heat increment is therefore all the heat produced by the act of eating, chewing, and digesting the feed and absorbing the nutrients from the gut.  When an animal is fasted, stored nutrients are used instead of absorbed nutrients. Heat increment represents the difference in the efficiency of using absorbed nutrients (fed animals) versus stored nutrients (fasted animal). Net Energy continued...  NE is the remainder of the “useful” energy after all the losses “available” to the animal and could be used for both animal maintenance and production purposes (e.g., milk, eggs, meat, etc.) NE = NE (maintenance) + NE (production)  NE represents the best scientifically designed energy system because NE is the actual amount of energy that is useful to the animals; it should be the best way to describe feed energy.  Nonetheless, we seldom directly measure NE systems due to the cost and difficulty of determining the NE values. The NE values in feed tables are derived from total digestible nutrients (TDN), DE, body weights, and regression equations based on experiments depending on the species. Methods for Measuring Heat Production and Net Energy Calorimetry:  Animals lose heat to the environment through conduction, convection, radiation, or evaporation. The latter loss is through the skin, respiratory tract, or excreta. Heat loss is measured directly using direct calorimetry or indirect calorimetry. Comparative Slaughter Technique:  In this test, live animal feeding trials are conducted by providing a common ration of known energy for a two week adaptation period. Calorimetry vs CST techniques Total Digestible Nutrients (TDN)  GE is of no value to the animal as it does not give any information on digestibility or palatability.  in the US, among the different energy systems, DE is commonly used in swine, and ME is commonly used in poultry. In ruminants, in addition to NE, TDN analysis is also used.  TDN is an old system of estimating the energy content of feeds. TDN is commonly used in ruminant animals  TDN is the summation of the digestible crude protein, digestible fiber, digestible nitrogen-free extract, and digestible ether extract and is expressed as a percentage of the total amount of feed.  The additional energy value of fat is compared to carbohydrates by the inclusion of 2.25 as a multiplier. Disorders Associated with Energy Intake Excess or inadequate energy intake can lead to several disorders in food-producing animals.  Obesity: Obesity is considered a disorder associated with excess dietary energy intake and is more commonly diagnosed in companion animals (e.g., dogs) and equines. Obesity can decrease the quality and length of the animal’s life. The greater the deviation from optimum body weight and body condition score (BCS), the greater the incidence and severity of orthopedic disorders and cardiovascular diseases. Bioenergetics: Summary 1. Bioenergetics is the topic of energy and its metabolism, or biochemical thermodynamics. 2. Energy is a concept and not a nutrient. Energy is the property of some nutrients. 3. The unit of energy is the calorie or kilocalorie. It is the amount of heat required to raise the temperature of one gram of water by 1° C. 4. Physiological oxidation happens inside an animal’s body through various metabolic pathways. Physical oxidation takes place inside a bomb calorimeter, which converts feed energy to heat. 5. Gross energy is determined in a bomb calorimeter. This provides a measurement of total energy in feed. 6. Digestible energy (DE) is determined by subtracting energy loss in feces from the gross energy (GE) of feed. Digestion trials are needed to get this value. Not all DE is retained by the animal. Bioenergetics: Summary 7. Metabolizable energy (ME) represents retained energy. 8. ME supports two different functions: tissue maintenance and production. Maintenance functions include all organ work (e.g., heart, lungs, kidneys) and ion balance and production include products (e.g., milk, meat, eggs). 9. ME is most commonly used in poultry, as feces and urine are voided together and easy to measure, while DE is more commonly used in swine. 10. Net energy (NE) accounts for all the losses and is theoretically more accurate. Bioenergetics: Summary 11. NE accounts for heat increment (HI), energy loss as heat. HI is heat production associated with nutrient digestion, absorption, and metabolism. 12. Methods to measure energy retention and heat production include direct and indirect calorimetry and the comparative slaughter technique. 13. Total digestible nutrients analysis uses digestibility and proximate analysis to provide an estimate of the energy content of a feed. 14. Disorders of energy metabolism include ketosis and obesity.