Term
| What is digestibility, and what is it measured as? |
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Definition
| Digestibility is the fraction of a nutrient that disappears from the gut, and it is measured as the difference between what goes in and what comes out in the feces. |
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Term
| What is apparent digestibility? |
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Definition
The fraction of nutrients dissappearing from the gut without regards for microbial fermentation products, endogenous protein sources, and/or mucous secretions, which are not utilized.
AFD=(nutrients in-nutrients out)/intake |
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Term
| How does the hindgut affect apparent digestibility? |
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Definition
| It adds proteins and energy to the tract via microbial fermentation. |
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Term
| What is true fecal digestibility? How does this differ from apparent? |
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Definition
| True fecal digestibility is the amount of nutrients absorbed from the small intestine; TFD=(nutrients in-nutrients out-nutrients from endogenous sources)/intake. Unlike apparent, true fecal digestibility accounts for nutrient sources in the hindgut that are not used by the animal. |
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Term
| Besides fecal digestibility, what is another way of measuring digestibility? How can this be done? |
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Definition
| Ileal digestibility is another method, and this can be done by cannulation, using a marker, and by performing ileal-rectal anastomosis surgery, where a tube is inserted into the animal's small intestine at the ileocecal junction, and the feed marker gives an idea of the nutrient concentration in the food. |
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Term
| Where would it be best to measure protein and amino acid digestibility? In the ileum or the feces? And why? |
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Definition
| Ileal method is best because in the colon, microbial fermentation of amino acids takes place, as well as sloughed cells and mucinous secretions, which affect the apparent digestibility. Protein digestion occurs in the small intestine, so measuring from the ileum will give an indication of how much protein was actually used. |
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Term
| Why is it not as important to measure fatty acids in the ileum when measuring digestibility as it would be for proteins? |
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Definition
| While microbials produce short chain fatty acids in the colon, they do not produces long chain ones. Therefore, it is more important for short chain fatty acids than for long. |
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Term
| Why can you measure minerals in the feces when determining their digestibility? |
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Definition
| Microbials don't produce minerals, and lots of mineral absorption occurs in the colon. |
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Term
| How does the physical form of feed impact digestibility? In particular, consider the size of feed particles- large vs. tiny and finely ground, and very, very tiny |
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Definition
| The size of the feed particle impacts the surface area that can be attacked by digestive enzymes- finely ground particles are more easily digested than larger particles, like whole grains, because they have a smaller surface area for attack. Very, very finely ground feeds can clump in the GIT and decrease digestibility. |
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Term
| How does a lower intake impact digestibility? |
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Definition
| Lower intakes signify higher digestibility because the animal doesn't eat as much, so less has to be pushed through the GIT. |
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Term
| What is gelatinization, and what does this do for digestibility? |
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Definition
| Gelatinization is heating starch with water, which incorporates water molecules between glucose polymers and increases digestibility. |
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Term
| What are important factors inherent to animals when considering digestibility? |
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Definition
The type of gut
Digestive enzymes available
Adequate dentition
Healty |
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Term
| Why does an herbivore have a greater apparent digestibility for proteins than a carnivore? |
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Definition
| Herbivores have longer GIT and hence the food is in the GIT for a longer time, so there is more time for digestion and absorption. |
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Term
| What will feeding high fiber to a monogastric animal do to digestibility of other nutrients? |
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Definition
| The other nutrients will become diluted, with an increased rate of passage through the GIT and less time for digestive enzymes to act. |
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Term
| Define availability of a nutrient |
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Definition
| The ability of a nutrient to be absorbed and used by the body; the nutrient is free from bonding to other molecules and from other chemical modifications that would stop its use in absorption or metabolism. |
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Term
| which amino acids are available to animals (D or L)? How might this be a problem in synthetic mixtures? |
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Definition
| L, although some animals can convert D to L. Synthetic mixtures are often racemic. |
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Term
| How does heat treatment impact availability? |
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Definition
| It denatures proteins and destroys vitamins, so although the food might be digestible, the amount of nutrients that can be absorbed and utilized is much less. |
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Term
| Problem with phytate and availability |
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Definition
| Phytate binds to phosphorous in food, and so the digestibility is reduced; as a result, phosphorous is excreted in the feces and presents issues with waste removal. |
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Term
| Differences between digestibility and availability? |
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Definition
| Digestibility assumes absorption- it is the fraction of a nutrient that disappears from the lumen of the GIT. Availability is the fraction of a nutrient that is able to be absorbed and is in a form that can be used; it is available to be metabolized. |
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Term
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Definition
| A reflection of the rates of metabolic pathways that utilize the nutrient in question, dependent on genotype and physiological/developmental state. |
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Term
| What are maitenance requirements? |
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Definition
| The amount of a nutrient needed to maintain a constant physiological state of well being. |
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Term
| What are four reasons why an animal would need more energy than maitenance would allow? |
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Definition
Illness
Pregnancy
Lactation
Growth |
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Term
| Define recommended daily allowance |
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Definition
| The recommended intake that reduces nutrient deficiency in some desired proportion of the population while avoiding excessive intake. |
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Term
| Define nutrient requirements |
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Definition
| The amount of a nutrient needed to maintain a given physiological state. |
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Term
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Definition
| Any chemical compound or element in the diet which sustains normal reproduction, growth, lactation, or maitenance |
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Term
| What are essential nutrients? |
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Definition
| Those which are required in the diet |
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Term
| What are the essential fatty acids? |
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Definition
| Linoleic acid, linolenic acid, arachidonic acid (carnivores) |
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Term
| What are the 11 essential amino acids? |
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Definition
| phenyalanine; valine; threonine; tryptophan; isoleucine; methionine; histidine; arginine; leucine; lysine; taurine |
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Term
| What are the main essential vitamins? Minerals? |
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Definition
vitamins: A,D,E,K,cobalamin,thiamine,riboflavin,panathanoic acid, niacin, pyridoxin, folic acid, biotin, choline
minerals: calcium, phosphorous, potassium, sodium, chloride, magnesium, iron, copper, manganese, zinc, iodine, selenium |
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Term
| what factors affect nutrient requirements? |
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Definition
type of GIT, age, type and level of productivity:
growth- nutrients to into making tissues, protein turnover
lactation- nutrients into milk production
reproduction- nutrients into fetus
physical activity
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Term
| What does the NRC do? What is the epidemiological approach to finding requirements? |
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Definition
| The NRC looks at different ways to define requirements. The epidemiological approach looks at the measurements of the intake of a given nutrient to a population of healthy animals. |
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Term
| What is the dose response approach? What are possible variables to use in measurement? |
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Definition
| Administration of various levels of a nutrient to animals, and measuring a particular response. Variables can be: weight gain, nitrogen balance, urea excretion, plasma urea concentrations, amino acid oxidation, prevention of clinical signs of deficiency |
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Term
| How would you use dose response to determine lysine oxidation? |
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Definition
| Feed diets with differing amounts of lysine, and measure the rate of lysine oxidation. Feed isotopes, then take sample of breath and look at carbon dioxide levels. |
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Term
| What happens if an animal lacks a particular essential amino acid in the diet? |
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Definition
| Protein synthesis can't occur, so the other amino acids get oxidized. |
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