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18 Cards in this Set
- Front
- Back
Digestible Feed |
The portion of a feed that is not excreted in feces and is assumed to be absorbed by the animal. Expressed as a coefficient or percentage |
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A cow eats 15 kg of hay DM and excretes 6 kg of DM in the feces. What is the digestibility? |
DM digestibility = (consumed - excreted)/consumed
DM digestibility = (15-6)/15 = 0.60 or 60% |
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In vivo method: total collection |
feed a known quantity of feed to the animal. Collect total decal output for 7 - 14 days after a minimum of one week of feeding. Analyze the feed and feces for the nutrient under consideration (could be DM, CP, NDF, EE, etc.) |
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In vivo method: indicator method |
feed a known quantity of feed with a known concentration of an indigestible indicator. This is your "marker". Collect fecal samples for at least 5 days after a minimum of one week of feeding the marker. Use indicator concentration in the feces to estimate fecal output: Fecal output = marker dose (g/day)/marker concentration in feces (g/kg) |
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Marker/indicator types |
may be a natural part of the feed (ex. lignin) or a chemical such as chromic oxide |
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Ex. An animal is given 10g of chromic oxide/day. Concentration in feces is 4g/kg decal DM. What is your fecal output? |
Fecal Output = marker dose (g/day)/marker concentration in feces DM (g/kg)
Fecal Output = 10/4 = 2.5 kg DM/day |
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In vitro method |
Lab method that simulates animal digestion. Non-ruminants - protein digestion determined by digesting feed in pepsin and HCl Ruminants - feed is incubated for 48hr in rumen fluid under anaerobic conditions. Bacteria are then killed by acidifying with HCl and digested with pepsin for 48 hr. |
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In sacco method for ruminants |
Ground feed samples (3-5g DM, 2mm in size) are placed in small nylon bags and put in the rumen of cannulated cows and incubated for 24-48 hrs. After incubation, bags are washed in ice water, dried, weighed, and contents analyzed. Digestibility determined using how much feed has disappeared inside the bag |
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In sacco method for pigs and dogs |
Animals are cannulated at ileum and fed a known amount of feed, the "ileal digesta" volume is calculated by using an indigestible marker. Digestibility up to the ileum is determined. |
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How feed composition affects digestibility |
- grains show less variability in digestibility than forages because of a more consistent composition - fibre fraction has the greatest influence on digestibility (more lignin = less digestible) - in ruminants, excess lipids inhibit rumen bacteria, thereby decreasing digestibility - low protein feeds cause low rumen ammonia. this causes poor microbial growth and, in turn, low digestibility |
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How diet composition affects digestibility |
- digestibility is influenced by a feed's composition, as well as the composition of feeds consumed with it - this effect is greatest when low quality forage is fed with a starchy ingredient like grain. Rapid fermentation of starch to VFA lowers rumen pH, decreasing fibre digestibility. |
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How feed preparation affects digestibility |
- excessive grinding of forages reduces digestibility of fibre due to rapid passage through the rumen - heat treatment of grains gelatinizes the starch, increasing digestibility - B-glucanase (an enzyme treatment) is added to barley diets for poultry |
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How does the level of feed intake affect digestibility |
Increased intake = increased rate of passage = decreased digestibility |
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Digestibility formula |
Digestibility = (nutrient consumed - nutrient in feces)/nutrient consumed |
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What can you do if fecal output can't be measured directly? |
use an indigestible marker to help estimate output |
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Digestibility can be measure using these 3 methods |
in vivo, in vitro, or in sacco methods |
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Why are digestibility studies a measure of apparent digestibility, not true digestibility? |
Measuring digestibility at the ileum is more true than at the feces which is apparent. Bacteria and sloughing that occurs in the hindgut doesn't get re-absorbed and contributes to the nitrogen content in the feces, which could be falsely contributed to the feed. |
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Digestibility varies with what 3 parameters? |
1. feed composition 2. diet composition 3. level of feed intake |