Feedstuff Evaluation Flashcards
what 4 things do you need to know when evaluating a feedstuff?
- nutrient composition
- presence of toxins
- palatability
- digestibility/nutrient availability
values of nutrient content of a sample are of no practical use unless?
the sample tested is representative of the feedstuff as it is fed to animals
how do you sample hay?
with a hay probe; stick into center of bale and get 12-20 total samples
how do you sample grass/pastures?
use a 1ft by 1ft square pipe; throw it, and collect areas at grazing height where it lands; repeat 12-20 times
how do you sample grain?
use a grain probe in the center of the grain bin 12-20 times
what is feed microscopy used for?
regulatory purposes; to make sure the feedstuff is actually made of what it claims to be
is feed microscopy very useful as a method of evaluation?
no; can check for presence of toxins or molds and such but nutrients are not visible so is not very useful
what is the proximate analysis of feeds?
a standard system of chemical methods of feed analysis; old but inexpensive so is widely used
what are the 5 aspects of proximate feed analysis?
- dry matter
- crude protein
- ether extract/crude fat
- ash
- crude fiber
describe the dry matter portion of proximate feed analysis
drying feed sample to a constant weight to determine water content
what does removing the water from a feedstuff allow for?
comparisons of nutrient content between different feedstuffs
what aspect of proximate feed analysis is always performed first?
dry matter!! will use dried feed for all further analysis
describe nutrient content before and after dry matter
nutrient concentrations are always higher on a dry matter basis
how is crude protein measured in proximate analysis?
estimated by measuring nitrogen content of feed multiplied by a factor of 6.25
nitrogen makes up what percent of protein?
16%
why is crude protein measure only an estimate?
because you are not directly measuring protein, but measuring nitrogen instead; but other feedstuff components contain nitrogen too so not super accurate, just a cheap measure
how is crude fat measured in proximate analysis?
extracting fat from a sample with ethyl ether
why is measuring crude fat also only an estimate of the amount of lipid in a feedstuff?
because you will also extract all other fats in the sample, including waxes which are not digestible
what does measuring ash in proximate analysis tell you?
measures inorganic portion, like minerals
what is used to get ash from a feedstuff sample? describe the process
a muffle furnace; heats to 500-600 degrees celsius and burns until all that is left of the sample is that ash
describe the efficacy of ash measurement
is a quantitative measure rather than qualitative since it does not tell you which specific minerals are in the feedstuff, just what amount; would need further analysis
what is the most useless of the proximate analyses?
crude fiber; not reliable and not very accurate
what does crude fiber measure?
the indigestible portion, which is usually fiber
how does measuring crude fiber work?
BOIL sample in a weak acid to mimic stomach, then BOIL in a weak base to mimic the small intestine, then filter and see what’s left
what are the 3 issues with the process of measuring crude fiber?
- the body does not BOIL!!
- acids and bases do not DIGEST, ENZYMES do
- does not measure microbial digestion
what are 2 methods that can be used to measure fiber other than the crude fiber method?
- NDF: neutral detergent fiber
2. ADF: acid detergent fiber, performed after NDF
describe the NDF method (3)
- uses a neutral detergent to solubulize cell contents of feedstuff
- leaves hemicellulose, cellulose, and lignin (the fiber portions)
- much more accurate than crude fiber
describe the ADF method (3)
- uses an acid detergent to solubulize hemicellulose
- leaves cellulose and lignin
- more accurate than even NDF
describe hemicellulose digestibility
more digestible than cellulose and lignin
what does the ADF method leave for evaluation?
the “true fiber” that the BODY can digest
does measuring fiber take into account microbial digestion?
no; microbes can digest all
what is nitrogen-free extract?
a calculated value that estimates the available/digestible carbohydrates
what does nitrogen-free extract also include in its measure? why?
vitamins; there is no proximate analysis to measure vitamins
why does the amount of vitamins indirectly measured in nitrogen free extract not matter?
it is such a small percentage, is negligible
how is nitrogen-free extract (NFE) calculated?
100-(water+CP+CF+EE+ash)
how do we estimate the energy content of feeds?
Total Digestible Nutrients (TDN)
what is TDN?
total digestible nutrients; sums all fractions of feeds that are digestible to measure energy
how do you calculate TDN?
digestible CP + digestible CF + digestible NFE + 2.25(digestible EE)
why do you multiply ether extract by 2.25 when calculating TDN?
because of the 4, 9, 4 rule: for every 1 gram of caarbohydrate there are 4 kcal, for every 1 gram of fat there are 9 kcal, and for every 1 gram of protein there are 4 kcal; 9/4=2.25, so fat has 2.25 times the amount of kcal as carbs and protein
what kind of indication of nutrient content does proximate analysis give?
a general indication
do methods exist to measure specific indications of nutrient content?
yes; they just go beyond proximate analysis and take extra time, work, and resources
define a kcal
the amount of energy needed to increase 1 gram of water by 1 degree celsius
what is gross energy?
the amount of heat produced when a feedstuff is completely oxidized
is gross energy useful to know about a feedstuff?
not really
how do you determine the gross energy content of feed?
by using a bomb calorimeter
what does measuring energy via use of a bomb calorimeter NOT tell us? give an example
tells us nothing about how the energy can be used by the animal
ex) if feedstuff is very fibrous, usable energy will be drastically different from gross energy
in what nutrient way will animals always try to eat?
animals will always try to eat to meet their energy requirements
describe the 4 levels of energy partitioning, including what energy is lost to at each level
- begin with gross energy, but energy is lost to fecal material
- what’s left is digestible energy, and some is lost to urine and gases
- after that is metabolizable energy, and some of that is lost to heat increment
- finally left with net energy, which goes to maintenance first, then production
what is digestible energy?
the amount of energy digested and absorbed by the animal
how do you calculate digestible energy?
DE = GE - fecal energy
describe the accuracy of digestible energy
much more accurate than gross energy, but doesn’t tell if or how the cells are using energy
what is metabolizable energy?
the amount of energy available for cells of the body to use
how do you calculate metabolizable energy?
ME = DE - urine energy - gas energy
how do you measure metabolizable energy? downside?
need specialized rooms with sensors that are very expensive, so we use general values instead
what is net energy?
the most accurate measure; tells what energy is used by the body for maintenance and production
how do you calculate net energy?
NE = ME - heat increment
what is heat increment?
the heat released during metabolism
how do you measure heat increment?
need another expensive ass room
what is net energgy SUPER important for?
determining energy requirements in dairy animals
what is digestibility?
the amount of feed that is ingested and absorbed by the animal
what does apparent digestibility NOT take into account?
- heat/gas losses
2. endogenous products which contain nutrients themselves (enzymes, wastes, old cells)
what are the 5 methods of determination of apparent digestibility?
- total collection in metabolism crate
- using collection bags
- nylon bags for ruminants
- using fecal marker
- ileal digestibility
what does true digestibility account for?
endogenous losses
what is used to calculate true digestibility?
standard values of endogenous losses for each species
describe total collections in metabolism crates (3)
- animal housed in a crate and fed a known amount of food
- ALL feces are collected
- nutrient content of both feed and feces is measured;
what is the formula to calculate digestible nutrients from total collection in a metabolism crate?
(feed nutrient - feces nutrient)/feed nutrient; multiply by 100 to get % digestible nutrient, measure one nutrient at a time
describe the total collection method in terms of ease and how long can keep animal in the crate
relatively easy method, but can only keep animal in crate for up to 2 days
what must you do to the animal before performing total collection in a metabolism crate?
have to fast animal beforehand to start fresh
describe using collection bags to measure digestibility (3)
- attach bag to hind end of animal to catch feces
- feed animal a known amount of feed
- measure nutrient content of feed and feces
use same calculation as total collection in metabolism crate
what is the downside to using a collection bag to measure digestibility?
bags aren’t comfortable for any animal; animal may try to remove bag
what are the nylon bags used to measure digestibility in ruminants?
mesh-like bags to allow microbe access
describe the use of nylon bags to measure digestibility in ruminants (3)
- place a known amount of feed in a nylon bag
- place bag in the rumen of animals
- remove bag after set amount of time and measure nutrient content of starting and end bag contents; the difference in the two tells digestibility in RUMEN
what are the downsides of using nylon bags to measure digestibility in ruminants?
- requires canulated animals, which are very expensive
2. only measures microbial digestibility, not any digestibility in any other part of the tract
what is the super cool advantage of using fecal markers to measure digestibility?
don’t have to do total feces collection! only need one sample!
describe the process of using a fecal marker to measure digestibility (4)
- adding an indigestible marker to the feedstuff at a known concentration (ex. stainless steel grit)
- collect feces when marker appears and measure marker concentration in feces
- measure nutrient concentration in feed and feces
- compare marker and nutrient concentration to measure digestibility
describe the expected concentration of a fecal marker in the feed versus in the feces
concentration of the marker should be higher in the feces, as everything else should have been digested
describe ileal digestibility as a way to measure digestibility (3)
- feed an animal a known amount of feed
- collect contents of ileum of small intestine
- measure nutrient concentration of feed and ileal content; the difference between the 2 tells what was digested
why is ileal digestion a good measure of digestibility?
ileum is the end of the site of nutrient absorption (small intestine) so gives a good idea of what all was digested and absorbed without fecal collection
what is the downside to measuring ileal digestibility?
also requires canulated animals
when canulating an animal, what must be done to the organ of interest and why?
attach organ of interest to abdominal wall to avoid spillage
