ANFS251 Week of 02.15.16
ANFS251 Week of 02.15.16 ANFS251
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Popular in Animal Science and Zoology
This 15 page Class Notes was uploaded by Rachel Schmuckler on Thursday February 18, 2016. The Class Notes belongs to ANFS251 at University of Delaware taught by Dr. Lesa Griffiths in Spring 2016. Since its upload, it has received 14 views. For similar materials see Animal Nutrition in Animal Science and Zoology at University of Delaware.
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Date Created: 02/18/16
February 11, 2016 – Animal Nutrition GI tract is a unique system providing the means by which an animal accomplishes: Digestion of food consumed Absorption of essential nutrients Conservation of water Synthesis of essential vitamins and other nutrients Gastrointestinal Tract and Nutrient Utilization Convert complex nutrient sources into forms that the animal can absorb and use Digestion – converting complex feed nutrients into absorbable forms Absorption – digested nutrients cross the cellular lining (membranes) of the GI tract Classification of Various Digestive Systems Based on type of diet o Herbivores – primarily plants o Carnivores – other animals o Omnivores – combination of plants and animals Based on digestive physiology o Monogastric o Ruminant Classification of Various Digestive systems Swine – omnivore, monograstic Poultry – omnivore, monograstic, complex foregut and relatively simple intestinal tract Dogs and cats – monograstic carnivores Horses and mules – monogastric herbivores Ruminants – consume and digest plant materials and are classified as herbivores (cattle, sheep, goats, deer, elk, many wild species) o Pregastric fermenters (versus postgastric) Gastric means stomach Fermentation chamber with a structure full of bacteria before the stomach – “rumen” Bacteria = main source of protein “Cecum” for postgastric fermenter Proventriculus = stomach Large the structure, more complex the diet Relative size can provide insight as to where digestion will take place Rabbit Monograstic herbivore Complex large intestine Big cecum Characteristics and Function of Digestive Tract Mouth and associated structures – beak, teeth, lips, tongue o Primary function Prehension and preparation of food Increase surface area, increase what is exposed to digestive enzymes/bacteria Cattle and sheep will masticate food only to a limited extent before ingesting Subsequently regurgitate coarser constituents and remasticate them Rumination – decreasing particle size to increase the surfaces where bacteria can attach Teeth o Herbivorous Incisor teeth adapted to nipping off plant material Molars with flat surfaces grind plant fibers o Ruminants No upper incisors depend on upper dental pad and lower incisors (i.e. sheep) o Omnivores Use incisor teeth primarily to bite off pieces of food (i.e. swine) o Avian No teeth Break and or claws reduce food o Carnivores Teeth adapted to tearing of muscle and bone Pointed molars are adapted for crushing bones and mastication of food Saliva and Swallowing o Good mixed with saliva and formed into bolus Bolus is coated with saliva (lubricated) o Other functions of saliva Keeping the mouth moist Aiding taste mechanisms Providing digestive enzymes Acting as a buffer o Salivary Amylase = enzyme Esophagus o Bolus is transported (swallowed) to GIT CNS controls contractions Peristalsis = contractions Ruminants have two way (regurgitation) Challenge of the horse is that it is only one way – commonly chokes Length varies considerably Rumination – moving the bolus from reticulorumen to the mouth Allows the animal to chew its cud Aids the digestion of fibrous feed components Glandular Stomach o All stomach/stomachlike structures function the same way Difference: Location of the stomach Pregastric = rumen Postgastric = cecum o Lined with specialized secretory tissues o Contractions of the muscles lining the stomach mix with the bolus gastric secretions Amount of muscle varies amongst species Horse challenge – lacks a muscular stomach o Buildup of fluid causes colic Muscles contracting to churn the fluids in the stomach to aid digestion o Regions of the stomach Nonglandular region – no digestive secretions are produced Cardiac region – lined with epithelial cells, secrete mucin Fundic region – three cell types Parietal – secrete HCl (chemical, not an enzyme) Neck chief – secrete mucin (protect the stomach from the acid) Body chief – secrete pepsinogen, rennin, lipase o Pepsinogen protein enzyme o Lipase fat enzyme o Rennin milk digestion Plyoric – has only the neck chief and body chief cells o Presence of food causes secretion of HCl and enzymes and begins contractions of muscular lining o Chyme The bolus becomes this acidic material resembling a thick slurry Enters the small intestine (primary site for enzymatic digestion) Small Intestine o Composed of duodenum, jejunum, ileum o Duodenum Bile Neutralizes the pH of chyme to 6.8 to 7.0 Emulsification of fat Pancreatic enzymes secreted into duodenum to break down fat Enzymes secreted by duodenum to convert proteins and carbohydrates into amino acids and monosaccharides o Lined with fingerlike projections called villi that increases surface area One cell thick for easy absorption Complexly vascular o Contractions mix the digested food and move it down the GI tract o Digesta pass into the jejunum and ileum Enzymatic digestion continues Primary sites for absorption of nutrients in monogastic animals Large Intestine o Cecum, Colon, Rectum o Microbial digestion o Most nutrients already absorbed No villi o Type/number of microorganisms depend on the amount of undigested food constituents Varies depending on the diet and species Prevent rapid changes of diet in any animal because it kills the healthy gut bacteria that are accustomed to that particular diet Good bacteria will die, bad bacteria will grow Bad health results (i.e. diarrhea) o Absorption of some organic acids and water o Relative length, diameter, and extent of sacculation vary considerable among species Much larger in herbivorous species (i.e. horse, rabbit) o Indigestible components are eliminated via the rectum Small ceca in hawks, large in grouse The big foregut (hoatzin), long midgut (emu), and long colon (ostrich) compensates for the small ceca Other Functions of the GI tract Major route for excretion o Liver Active site of detoxification Some excretion of mineral elements Some net excretion in large intestine Depends on level of mineral stores in the animal and the number of minerals in the diet Synthesis of specific nutrients by microbial organisms Amount of absorption after small intestine is limited, so mostly are excreted o In some animals (particularly rodents and horses) this potential lack of absorption is circumvented by coprophagy Enables an animal to survive on diets lacking sufficient vitamins and amino acids Material excreted from cecum separately from that of the small intestine (different poops) Cecal pellets are nutrient rich from the vitamins made by bacteria in the cecum o Immediately eaten by the animal Avian Species Crop: temporary storage Proventriculus: similar to stomach, gastric secretions produced, less grinding action than the stomach Gizzard: tough muscular lining contracts Crop, proventriculus, and gizzard together function as a stomach, but the proventriculus contains the acids/enzymes, the crop is the storage, and the gizzard is the movement Relatively long small intestine Two rather large ceca – located in the large intestine (past the main site of absorption) so the ceca do not contribute highly to the ability to consume a high forage diet, not very functional Very short sections of large intestine o Urinary secretions are combined with the feces before being eliminated Ruminant Species Stomach o Divided into four compartments Reticulum – honeycomb Rumen (name for the entire “stomach” structure, but also a part of the 4 compartments) Aka Paunch Allows for a high forage diet Located before the small intestine Contains bacteria, nutrients absorbed Tonguelike projections called papillae Several strong, muscular pillars which contract in a rhythmic manner Causes ingesta to be mixed o Course fibrous feeds regurgitated and rechewed Omasum Contains varioussized leaves extending into the lumen to prevent large particles from leaving the rumen Abomasum Same function as the glandular stomach in monogastric species o In pseudoruminants, the stomach has only three compartments Camel and related species Ingested food subjected to pregastric microbial fermentation Small intestine – similar to monogastric species o No benefit to feeding ruminants high quality protein because the bacteria eat it regardless, and they get a good amount of protein from consuming that bacteria Bacteria break the feed into volatile fatty acids (VFAs) Absorbed from cecal wall From sugars and starch Absorbed and sued as primary energy source Readily used but less efficient than if original carbs were digested and asbored from small intestine 820% of carbs consumed converted to methane (wasteful!) Nonruminants must break food into glucose for energy Large intestine – considerably larger than omnivorous species Digestive tract of a sheep Large rumen for microbial fermentation! – main contribution to digestion Small intestine = absorption Cecum not as useful, some fermentation, reabsorption of water Rumination Undigested coarse foods are collected in the reticulum Formed into a bolus Moved back up and the esophagus to the mouth for further chewing Eructation Belching of gas Microbial fermentation in rumen produces gases (CO2 and methane) which must be eliminated to avoid bloat o Occurs when froth forms in the rumen o Usually after consuming legume species, or a highconcentrate diet (i.e. grains) o Can inhibit eructation o Results in reduced performance and many deaths (pressure on other organs) o Cattle swell on the left side Symbiosis Mutually beneficial relationship between rumen microorganisms and animals Very favorable environment for microbes – moist, narrow temp range, feed source, end products removed Many bacteria types (2580 billion per ml) Ciliated protozoa o 35+ species o 20,00050,000 per ml Type of organisms depends on feed consumed o High forage diet High in cellulose and hemicellulose Relatively in digestible in mammals Microorganisms digest those substrates o Same for diets high in cereal grains but for starch o Number of organisms affected by feed intake o VFAs and ammonia (nitrogen to amino acids to protein) are end products of microbial digestion Continually absorbed across rumen wall When microbial populations thrive, it greatly affects nutrient requirements of the host animal Fibrous digested more efficiently by microbes in the rumen Cellulose and hemicellulose digested only by microbial enzymes Bacteria can use simple forms of nitrogen (i.e. urea, ammonia) to synthesize cellular proteins, reducing dependence on highquality dietary protein sources Microbes synthesize adequate amounts of vitamins Except A, D, and E – fat soluble No need to worry about giving ruminants water soluble vitamins Moisture and pH of rumen are maintained by the 150+ liters of saliva secreted per day in a mature cow Contains large amounts of sodium bicarbonate o Acts as a buffer and neutralizes acids produced in the rumen Disadvantage: High quality dietary protein sources are partially degraded to produce ammonia o Resynthesized into microbial protein (medium quality protein) Advantage: Low quality dietary protein sources are partially regarded when consumed by bacteria “Pounds per feed per pound of gain” More pounds of feed for ruminants because feeding bacteria before the animal Overall effect of rumen fermentation = animals utilize good quality ingredients less efficiently than monogastric animals Differences in feed types and how they are digested illustrate why feed conversion in ruminants is low Young Ruminants Born with nonfunctional rumen o Depending on digestion in the abomasum and small intestine o Reticular (or esophageal) groove Allows milk to bypass reticulorumen Goes directly to omasum and then abomasum Escapes bacterial fermentation Start to consume solid food o Reticulum and rumen start to develop o Fully functional by 8 weeks in lambs and 69 months in cattle Differences with Respect to the Types of Diet for Different Species Avian species do not have the ability to effectively utilize large amounts of fibrous plant materials Omnivorous species (i.e. swine) can utilize more fiber than avians, but much less than herbivorous species o Adult omnivores do better than young omnivores o Well developed ceca o Less complex digestive tracts, limited ability to digest fibrous plant carbs Nonruminant herbivorous species (i.e. horse) can survive and do well on plant materials of much lower quality than that required by swine o Hindgut fermenters o Developed ceca o No coprophagy Ruminant animals are well developed to diets that consist primarily of fibrous plant materials o Pregastric rumen o Poor efficiency tons of food to get nutrients because the bacteria need to be fed before the animal (caloric cost) Monogastrics use the calories immediately o Simple stomach and intestines o i.e. poultry o Fed highly digestible diets with high quality nutrient sources Nutrient Utilization Animals that can use large amounts of forages have a stomach or large intestine that allow either: o Pregastric microbial fermentation (ruminant) o Postgastric microbial fermentation (horses, rabbits) Carbohydrates Primary component found in livestock feeds Why not protein? o Necessary for young animals to grow o Older animals use it for repair o Very expensive form of energy Why not fat? o Expensive o Little supply due to human demand Carbs o Abundant o Inexpensive Carbohydrate = energy! Bulk of the diet Forages Corn – highly digestible starch Synthesized by plants Primary building block in most plant materials = glucose Primary subunit of glucose = carbohydrate Many different types of carbohydrates coming from different parts of a plant Comprise up to 70% of forage dry matter and 80% of grains No specific dietary requirement for carbohydrates, but rather for energy (calories) Types Composed of C, H, O Simplest form = monosaccharide o 5 carbon monosaccharide = pentose o 6 carbon monosaccharide = hexose Disaccharide = two monosaccharides combined Polysaccharide = 3+ monosaccharides combined o Complicated polysaccharide chains are indigestible by mammals (only by bacteria in the rumen and cecum) Types of carbohydrates associated with feeds: Common Carbohydrates Glucose and fructose – most common simple sugars in feed Sucrose o Glucose + fructose o Found in plants as sugar cane and sugar beets o Highly digestible Lactose o Glucose + galactose o Only in milk o Lactose intolerant = no enzyme to break apart the glucose and galactose Maltose o Glucose + glucose o Intermediate breakdown product produced when starches are digestible Starch and Cellulose o Polysaccharide in plants in the highest concentrations o Starch Grains (i.e. corn), tubers, and other roots Links between glucose subunits can be easily digested by mammalian enzymes Sweet taste o Cellulose Forages (in the stalks of plants) Links between glucose subunits cannot be digested by mammalian enzymes Digested by microbial organisms in GIT Gums, pectins, hemicelluloses o Occur in varying amounts in some plant material o More indigestible than digestible Absorption and Metabolism Monogastrics o Dietary carbs converted to monosaccharides o Amylase Salivary glands of some species Primary source = pancreas Starch to maltose o Other enzymes from mucosal lining of the duodenum o Corn, milo, barley, oats = common Dietary carb levels exceed animal’s ability to digest it - diarrhea occurs Monosaccharides rapidly absorbed by small intestine and transported via blood to be metabolized as an energy source Storage o Little stored as carbohydrates o Some glucose stored as glycogen Rapid release in muscular activity Regulation of blood glucose No enzymes to digest cellulose, hemicellulose, and other carbs in fibrous feedstuffs o Occurs in rumen, cecum, colon from microbial action with varying success Monogastrics: horses > swine, rabbits > poultry, dogs, cats Ruminants o Young ruminant animals are functionally monogastric Eat solid food Bacterial and protozoal populations gradually develop in the rumen Microbial organisms produce VFAs Papillae in rumen to develop and mature, enabling the animal to digest more complex carbohydrates (cellulose, hemicellulose) o Fully developed rumen
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