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Animal Science
ANSC 303
Josie Cloverdale

Digestive Systems and Digestion Why do animals digest feed? • Food not ingested in a suitable state ◦ Needs to be crushed, enzymatically broken etc • Physical nature of feed determines ◦ Gathering apparatus for uptake ■ Huge if you work at a zoo - have to mimic whats in nature ◦ Type of Digestive system required for digestion • Happy healthy animal is more effective to the producer Functions of Gastrointestinal System • How do you use what you eat? Main difference between species • Digestion (most basic function) ◦ Taking a unit and making it small enough to pass the wall of the gut, big structure to small ◦ Enzymatic (in stomach and SI) vs. fermentation • Absorption ◦ Moving that small piece that was digested from the gut to the blood, crossing single cell layer • Protective barrier ◦ Why we can consume semi sketch food ◦ Germs are everywhere but its how many we consume that makes the difference • Immunological function ◦ We interact with the things in our gut without knowing it • Metabolism • Endocrine (hormone) ◦ Gut interacts with body, some foods or diets affect hormones differently and make you not feel full leading to obesity • Digestion and Absorption is never 100% efficient so there will be waste, and since we want as least amount of waste as possible it is very important Basic Organization • If its big its important!!! • Arrangement of organs ◦ Mouth ◦ Esophagus ◦ Stomach ■ When we first see differences between monogastric vs a ruminant ◦ Small Intestine ■ 90% of digestion occurs in Small Intestine, similar among species ◦ Large Intestine ■ Is either highly developed or simple ◦ Anus • Associated Structures- Outside of GI series, can also control metabolism ◦ Salivary glands ■ huge for ruminants especially ◦ Pancreas ■ where majority of digestive enzymes come from, very important ◦ Liver ■ Orchestrates movement of nutrients of tissue, if it has to be modified or metabolized ◦ Gallbladder ■ Storage vesicle for the bile in the liver ■ horses are the only ones that do not have a gallbladder You are what you eat…. • Herbivore ◦ Consumes only plant material ◦ Can make good use of low quality plant based diet and convert it to higher quality meat ◦ Intermediate to convert to higher quality • Carnivore ◦ Consumes only meat ◦ Compete with us • Omnivore ◦ Consumes both plants and meat ◦ In livestock we feed them plant based products, or very minimal meat • Cats- strict carnivores, can't really make anything • Dogs- omnivores • Poultry- omnivores • Sheep- herbivores • Pigs- omnivores • Horses- herbivores Form to Function • Pigs ◦ Humans are almost identical to pigs, use rats and mice because of cost reasons ◦ Pig is standard monogastric model, very balanced GI tract ◦ Very proportional throughout • Chicken ◦ Monogastric but has more compartmentalization ◦ Don't have teeth so will need a part of the Gi to grind feed ◦ Urine and fecal material are combined • Horses ◦ Technically mono gastric ◦ VERY enlarged large intestine ◦ LI very important to horses ◦ monogastric herbivores is difficult so thats why they have such a large LI because that is where fermentation takes place • Ruminants ◦ Have compartmentalized stomach (3-4 compartments) ◦ Very large stomach so its very important ◦ Feed bacterial population basically, symbiotic relationship Basic Digestive System Types • Monogastric or Non- Ruminant ◦ Very proportional ◦ No compartments in the poultry that are bigger than another flexible GI system • Ruminant ◦ Converts low quality forage to make high quality product ◦ Are usually bi-products of human consunmation (soybean meal) ◦ Very small SI and LI (like tiny) ◦ Psuedoruminants are missing compartment (only have 3 compartments) ■ Are missing the Omassum • Monogastric- Hindgut Fermentation ◦ Enlarged LI compartment so smaller stomach and SI ◦ Allows them to live off of herbivore diet Comparative Physiology- Starting Simple! • Mink ◦ Simple stomach ◦ Short intestine ◦ No cecum ◦ Carnivores, high protein and fat nutrient input- very easy to break down in stomach and SI ◦ Will have a fairly large stomach and SI, tiny LI so they can't ferment plants (similar to feline species) • Dog ◦ Simple stomach ◦ Short intestine ◦ Small cecum ◦ Dogs prefer meat so they have a larger stomach and SI but they do have a cecum and LI, minor fermentation capability Comparative Physiology- Simple Stomachs • Pig/Human ◦ Simple stomach ◦ Longer intestine ◦ Cecum and colon sacculated ◦ ⅓ stomach, ⅓ SI, ⅓ LI ◦ ***Sacculation are the speed bumps of the GI tract, so they have more time to break it down(where the bacteria break it down), fermentation takes hours so we need to slow down mvmt through tract ◦ Hard to maximize this system so its a little more expensive because they don't do anything great • Horse ◦ Simple stomach ◦ Short small intestine ◦ Voluminous cecum and colon ◦ Horse has tiny stomach, shorter than SI than pig ■ Food will move very quickly so not as much gets digested ◦ Gigantic cecum, large colon, long small colon, ■ Lots of fermentation for plant based material, can live off of pasture alone Comparative Physiology- Foregut Complexity • Chicken ◦ Complex foregut ■ 3 sections ◦ Simple intestines ◦ Have not teeth ◦ Food goes to crop which is a holding area and controls the control of release of food to other areas of the tract ◦ Proventriculus- where the enzymes are exposed, serves as a stomach, first initial breakdown of food ◦ Gizzard- contains rocks and dirt and makes up for not having teeth and and breaks down particle size ◦ Tiny SI connects gizzard to cecum, further digests small particles ◦ Tiny cecum, large intestine where they can ferment ■ Not a lot of fermentation capability ◦ Small particle size to help them digest faster, don't have to eat as much ◦ Cloaca/ vent- fecal and urine are one Comparative Physiology- Foregut Fermentation • ***Ruminant- sheep, cattle, goat • Sheep ◦ Compartmentalized stomach ■ Four compartments which house bacteria and provide fermentation ■ Slow down rate of passage, 60% of tract ◦ Long Small intestine ■ Ruminant feeds product to the lengthy SI, absorb things from factory ◦ Short and simple cecum and colon ■ LI is tiny, don't need to ferment twice, absorb some water or anything that escapes • Kangaroos ◦ Stomach sacculated and voluminous ◦ Short cecum/colon ◦ They are technically mono gastric ■ Their stomach looks like part of the LI or cecum, provides fermentation ◦ Plant based, can ferment in stomach Mouth • Functions ◦ Take in food ■ Prehension differs with species ◦ Taste ◦ Chew(masticate) ■ Teeth vary with species ■ Reduces particle size ◦ Mix with saliva • Cattle(ruminant) have a huge tongue- their prehensile organ, only have a few teeth • Horses use teeth and lips (lips have most dexterity because they have the largest number of nerve endings) • Swine just use lower jaw like a shovel • Poultry use their beak to get things and knock it back • Mouth takes in food and tastes it Mastication • Physical reduction of feed ◦ We chew to reduce particle size so we can increase surface area for enzymes and whatnot (extremely important for herbivores) • Especially important in non- ruminant herbivores • Adaptations- everyone does it slightly different ◦ Carnivores- large canines and incisors ■ Tearing but little chewing ■ Don't have to grind as much because their product is easy to digest ◦ Herbivores- specialized molars, HUGE ■ Lots of chewing and grinding ◦ Teeth are essential for proper mastication ■ If longevity is an issue teeth become a problem/ concern Structural Adaptation of Teeth • Omnivore is combo of everything • Ruminants have a dental pad, tongue brings product into mouth and pull with the tongue and dental pad ◦ Typical in cattle, sheep, etc Saliva • Functions ◦ Lubricates feed ■ Helps you not to choke ◦ Start enzymatic digestion? ■ Species dependent ■ Mainly of carbohydrates (starch) ■ Most ruminants don't digest in the saliva, don't need it ◦ Buffer ■ Primary buffer is bicarbonate- actually feed it to them but saliva does it on its own **** Cattle use waaaay more saliva than horses (even though they have a similar size), cattle go through rumination which means they chew everything twice • Composition ◦ Water ◦ Inorganic components ■ Minerals ■ Buffer ◦ Organic compounds ■ Urea- ruminant specific (nitrogen recycling) ■ Enzymes- monogastric ■ Amylase- breaks down starch ■ Lipase- breaks down fat ■ Mucoproteins- mainly for nursing, breaks down milk, why saliva is slimy • Production depends on species Esophagus • Muscular tube ◦ Lubricated by saliva ◦ Doesn't make anything • Pharynx to stomach (cardia) ◦ Way to get to stomach • Striated ----> smooth muscle ◦ Striated for first ⅔ and then go to smooth • Dogs and ruminants striated throughout ◦ Ruminant have striated for regurgitation purposes daily, need to control and you can get it through having striated muscle ◦ Dogs is an adaptation- feed their young through regurgitation when transitioning to solid food • Angle of attachment in horses discourages regurgitation ◦ Horses can't regurgitate EVER Reticular Groove • IN RUMINANTS ONLY • Also called esophageal groove • Muscular contractions close the groove (reticulum) ◦ Acts like a funnel ◦ Normally feed drops to reticulum, when you consume milk the groove closes and is sent to the abomasum • Allows milk to pass from esophagus directly to abomasum ◦ By-passes rumen (3 other sections of the stomach) ◦ Don't want to ferment milk! Why some calfs bloat • Groove converts ruminant to monogastric ◦ Suckling reflex makes groove function Stomach • Monogastric (non- ruminant) ◦ One compartment- size varies ◦ Have a lot of differences in capacity, but parts and function stay the same throughout species • Ruminant ◦ Huge regardless of species ◦ Arrangement and function of all compartments is important ◦ 1 organ, 4 compartments (¾ of abdominal cavity- in order) ■ Reticulum ■ Rumen ■ Omasum ■ Abomasum Glandular Stomach • Stomach in monogastric, abomasum in ruminants • Have glands that release secretions • Last stop before SI for both types, if it needs to slow down or speed up it happens here • Functions ◦ Mixing of food ◦ Reservoir for controlled release into small intestine ◦ Production of HCl and pepsinogen ◦ Limited absorption ■ Aspirin, alcohol (these are the only things that it can absorb into the bloodstream) Stomach Anatomy • Regions: ◦ Esophageal ■ Non- glandular ■ Where esophagus attaches to stomach ■ Non glandular, no secretion ◦ Cardiac ■ Mucus ■ In the top region ■ Opening between stomach and esophagus ■ Its a sphincter ◦ Fundic ■ Mucus- secretes the most, and a lot of it ■ HCl (parietal cells*) ■ Pepsin (chief cells*) ◦ Pyloric ■ Sphincter that separates stomach with pyloric region ■ Mucus *These cells are protected by mucus *** Abomasum functions in a similar manner Stomach Secretions • HCl- parietal cells ◦ Denatures protein ◦ Kills bacteria ◦ Activates pepsinogen- most important function ◦ Ruptures starch granules- unfolding of starch as well • Pepsinogen- chief cells ◦ Activated to pepsin by HCl ■ Need to be able to control it because the stomach(protein) has to be protected ◦ Pepsin starts protein digestion ◦ Clots mlk • Rennin- Abomasum ◦ Clots milk to slow down rate of passage ◦ Helps milk digestion process ◦ Used in cheese and dairy industry, create synthetic version • Stomach is a mixing apparatus and preparation phase Ruminant Stomach • Anatomy is important*** • Abomassum in the right side, rumen on the left • Liquid and feed particles ion the bottom, a lot of forage in the diet floats • On the line we have fiber mat, there's layers and fractions • Fiber mat important in remastication Rumen Development • Only abomasum developed in newborn ruminant ◦ Calves born with very large abomasum ◦ Little fermentative capability ■ Size ■ Musculature ■ Microbial population • Development requires solid feed and microbes ◦ Solid feed is easier and cheaper ◦ Only thing that can help development of other compartments ◦ Sooner I can ween them off milk the better • 2 to 3 months of age Influence of Diet on Rumen Development • How does diet impact the factor involved in rumen development? ◦ Size and musculature ◦ Papillae development- fuzzy shag carpeting projections ◦ Microbial populations • Milk Only Diet: very thin tissue, small • Milk and Hay and Grain: thicker, bigger, gray color, indicates that the tissue is active and doing its job ◦ Shag carpeting effect is good, increases microbial populations • **Hay doesn't do as much for fermentation as much as grain does Size of Stomach Compartments • Regardless of species rumen is always the largest • Omasum has the most variation: very small in sheep, large in cattle, not that important • Other compartments are relatively similar • What is a pseudo- ruminant? ◦ 3 compartment animal, missing omasum, can live without it Function of Compartments • Reticulum- first compartment ◦ Honeycomb appearance ■ Studded with small papillae ■ Absorptive cells of reticulum and rumen, projected into organ which increases surface area ◦ Fermentation ■ Where fermentation and digestion starts ◦ Traps objects ■ Hardware disease- caused by a puncture, infection ■ Moo magnet holds on to metal objects in reticulum, in slaughter house it is removed • Rumen ◦ Papillae ◦ Fermentation ■ Absorption of VFA (volatile fatty acids), NH3 (ammonia), and water ■ These can all be absorbed here ■ Ammonia is part of nitrogen recycling ◦ Rumen separation just moves and floats, no valve or anything ◦ Commonly lumped with reticulum ◦ Lar
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