Lab Exam Flashcards
Why are samples of feedstuffs dried before conducting proximate analyses?
different feedstuffs contain variable amounts of moisture. By dying the sample, comparisons can be made consistently (on a dry matter basis)
what are 2 things we should know before we formulate an animal’s diet?
- nutrient content of the feedstuffs
- digestibility of the nutrients
- also must know the requirements of the animal!
what is slack space?
the space in the diet that we reserve for the potential addition of supplements (such as a premix)
why do we include slack space?
so that adding supplements won’t dilute the content of protein and energy
do we need to worry about slack space when using the computer?
No, because the computer can calculate all possible combinations of ingredients (including the supplements) to meet our specifications
Formulate a diet for pigs with 21% protein, using only wheat and barley.
Barley= 11% protein
Wheat= 14.5% protein
Is this possible?
No
both ingredients contain less than 21% protein
There is no mixture of these ingredients that will contain 21% protein
What happens if you overmix a feed?
overmixing can lead to the separation of more dense ingredients (they fall to the bottom)
this results in an uneven mixture of ingredients and nutrients
the expected level of intake of feed is highest for __ (best/ worst) quality feed and lowest for ___(good-poor) quality feed
best
poor
T/F
A diet will be infeasible if an ingredient included is too expensive
false
the computer selects the lowest cost possible, but doesn’t care HOW low that cost is
How would you tell the computer to formulate a diet with exactly 3000 kcal ME/ kg?
set both the minimum and maximum constraints for the nutrient energy to 3000
How would you tell the computer to formulate a diet with no more than 5% vegetable fat in a particular ration?
set a max constraint of 5% on the ingredient vegetable fat
Synthetic amino acids are very expensive ingredients, yet often the diet cost decreases when we allow the computer to use these ingredients. Why?
Although they’re expensive, very small amounts are required, thus adding little cost to the diet.
To get the same increase in a specific AA using a protein ingredient (such as soybean meal) = you have to add a substantial amount of that ingredient, which increases the cost more
give an example of a “product”
a complete diet such as “pig grower”
give an example of some nutrients
sodium calcium Met + Cys crude protein "metabolizable energy"
give examples of ingredients
corn
wheat
canola oil
salt
give an example of something that is both a product and an ingredient
vitamin-mineral premix
what is the first step in determining the nutritive value of a given feedstuff
proximate analysis
= an estimate of what is in a complete feed or feedstuff
T/F
proximate analysis gives enough information to formulate diets; it is very rapid but expensive
false
- not enough info to formulate diets
- rapid
- inexpensive
feedstuff samples contain - - - -
- ash
- fat
- protein
- carbohydrate
Dry matter=
Ash + fat + protein + fiber + Nitrogen-free extract
what is the purpose of sample grinding in proximate analysis?
- makes it homogeneous (better mixing of sample)
- increases surface area
explain the principle of ash
- organic matter will burn
- minerals will not burn –> the residue left after all organic matter has burned off is minerals
what are 2 assumptions we make when doing crude protein analysis
- all nitrogen is associated with protein
- all protein is 16% nitrogen (100%/16%= 6.25 conversion factor)
-
- true proteins
- non-protein nitrogen (amino acids, urea, amides, etc)
ether extract contains
- lipids
- plant pigments like chlorophyll
- waxes
crude fiber is ___ material of ___ (high/low) digestibility
carbohydrate
low
- low nutritive value for monogastrics
- can be of high nutritive value for ruminates via microbial digestion
in ____-based ingredients, only ___ of the phosphorus is available to the ___ animal
plant-based
1/3
monogastric
(so divide total P by 3 to get available P for monogastrics)
what percentage of total phosphorus is available to ruminants?
100%
total P= available (digestible) P
why is digestible ether extract multiplied by 2.25 when calculating TDN?
because of the higher energy content relative to protein and carbohydrate
why are water and ash not included in TDN calculations?
because they do not contain energy
what is the formula for digestible energy
( (total energy fed)- (total energy excreted) ) / (total energy fed)
what is the formula for metabolizable energy
= ( feed gross energy - fecal GE - urinary GE ) / (feed intake)
