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How does the horse's digestive system work?
esophagus > stomach > small intestine > cecum > large intestine
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What makes up the large intestine?
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Where does fermentation occur?
hind gut
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How big is the stomach's holding capacity?
4 gallons
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How much can the cecum hold?
15-20 gallons
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How much does the large intestine hold?
30-35 gallons
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How fast is gastric digestion?
15-20 minutes
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How long does food stuff sit in the small intestine?
45 minutes-3 hours
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Is digestion in the hind gut fast or slow?
slow
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How long does the cecum take to digest?
48-72 hours
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How does the lower jaw move?
rotates in a circular motion
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How much saliva do horses produce?
- up to 3 gallons a day (15mL/minute during feeding)
- only when they chew
- helps lubricate food
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What is the purpose of gastric digestion?
opens up nutrients for small intestine
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What does amylase do?
breaks down starch and is found in the saliva
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What does bicarbonate do?
helps buffer the system and is found in the saliva
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Why aren't horses able to vomit?
have a sphincter valve that doesn't allow food back up the esophagus
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What occurs in the stomach?
- gastric digestion (particle breakdown)
- start of protein digestion
- minor microbial fermentation (small microbes break down cellulose)
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What is pepsin?
responsible for breaking down proteins and is secreted in the stomach
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What occurs in the small intestine?
- enzymatic digestion (pancreas)
- primary site of nutrient absorption
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What is lipase?
breaks down lipids and fats
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Why are lipids important?
responsible for moving fat-soluble vitamins
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How do lipids move?
- carried on bile salts
- not water soluble
- only absorbed in upper part of the small intestine
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What makes up the hindgut?
- cecum
- large intestine (large and small colon)
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What makes up the foregut?
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What do microbes in the cecum do?
- break down fiber from forages
- produce volatile fatty acids, methane, and b-vitamins and k-vitamins
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What can kill microbes if not broken down?
- starch and protein
- they release toxins if microbes are killed
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What happens in the large colon?
- Volatile Fatty Acid synthesis and absorption
- B-vitamin synthesis (need water to be absorbed)
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What happens in the small colon?
- Water re-absorption
- development of "horse apples"
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Does the large intestine have microbes?
Some in small amounts
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What are the 6 classifications of nutrients?
- energy-carbohydrates
- lipids-fats
- proteins
- minerals
- vitamins
- water
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What are carbohydrates?
- Primary energy source
- starches/simple sugars and fiber
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What are structural CHO?
- Starch/simple sugars
- found in the grain of hay
- easy to break down
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What are structural CHOs?
- Fiber
- important for microbes in hind gut
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What affects the quality of fiber?
- Cellulose
- Hemicellulose (harder to break down)
- lignin (non-degradable)
- pectin (plant sugar)
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Describe lipids (crude fat).
- 2-3 times as much as glucose
- needed to make fat-soluble vitamins
- usually supplemented (more than 4%)
- 10%-20% can be fed
- ex: soy bean oil, fish oil, rice bran
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What happens if there is a crude fat imbalance?
- not enough fat for energy=lose weight
- too much fat=gain weight
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What is the importance of protein (crude protein)?
- essential in growth and performance
- helps with amino acids (building blocks of tissue)
- needed in tissues, muscles, metabolism and body functions
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What happens if there is a protein imbalance?
- young horse> affects growth
- performance horse> muscle atrophy and poor performance
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What are the most important macrominerals?
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What is the ideal calcium to phosphorus ratio? why?
- 2:1
- absorbed in two different areas and you don't want one to be wasted
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What happens if there is a mineral imbalance?
issues with deficiencies and toxicities
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What are the fat-soluble vitamins and why are they important?
- Vitamins K,A,D,E
- needed for body functions
- produced by plants themselves (most available directly after plant is cut)
- can be toxic if overfed
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What is important about water-soluble vitamins?
- needed for body metabolism
- manufactured in the hind gut
- can be flushed out if overfed
- similar to an energy drink
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How much water does a horse drink per day?
- 6-8 gallons for 500kg horse at rest
- 12-18 gallons for 500kg horse exercising
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What do you need to know to figure out nutrient requirements?
- body weight
- physiological status
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What nutrient requirements do idle horses have?
- need enough energy to maintain healthy body weight
- 5-6 BCS
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What nutrient requirements do broodmares have?
- be able to provide for fetal development
- 6 BCS
- maintenance diet up to 5 months of gestation
- after 5 months, need more energy, crude protein and calcium
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What are the nutrient requirements for broodmares in late gestation?
- need more trace minerals
- high quality hay and pasture
- up to 5lbs of grain per meal 2-3 times a day
- more concentrates than forage
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What are the nutrient requirements of lactating mares?
- be able to maintain milk production and rebreed
- need high quality forage
- need more energy and crude protein
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What are the nutrient requirements of growing horses?
- need to reach genetic potential and have sound skeletal development
- need high quality forage and feed formulated for growth
- need energy for growth
- need protein for skeletal/muscle development
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What happens to growing horses if there isn't enough protein, calcium, phosphorus and energy?
- stunted growth
- abnormalities
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What are the limiting amino acids for growth?
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can essential amino acids be made in the body?
no
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What is the peak weight gain for growth?
16% CP
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How is low CP fortified?
with lysine and threonin
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What are the nutrient requirements for working horses?
- have enough energy to complete exercise and have optimal performance
- need high quality forages and grains formulated for work
- need extra starches, carbs, etc., to meet energy needs
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What are the major nutrient concerns for working horses?
- meeting energy requirements for the work
- replacement of water and electrolytes lost in sweat
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What are the protein requirements for working horses?
- more than idle horses (10-12% CP)
- need nitrogen back in the system
- too much CP causes more urea, more excretion, more heat and more acid produced
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What does feeding fat do?
- safe, dense energy source
- provides essential fatty acids
- increases absorption of fat-soluble vitamins
- provides calming effect
- feed plant based fats (soy bean oil, vegetable oil)
- 8-10% but not over 20%
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What are electrolytes?
- found in plasma and easily lost through sweat
- can be lost in metabolism
- can be provided by food but the body can't store them
- sodium, chloride, potassium
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What are the nutrient requirements for senior horses?
- needs less energy than younger horses because body is breaking down
- needs less protein for metabolism because GI tract is breaking down
- mineral requirements are not known
- need an easily digestible feed
- maintain good BCS
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