feed analysis topic 4 Flashcards
define digestibility
proportion of foodstuff which is not excreted in faeaces, therefore assumed to be used by the animal
commonly called in terms of dry matter %
what are in vivo measures of measuring digestibility?
benchmark
measure actual digestibility of feed stuff within the animal
expensive and time consuming to conduct
- diff between dry feed offered and amount excreted
what is the indicator method of measuring digestibility?
indirect measure of digestibility
using a known indigestible substance to its concentration in the faeces
digestibility %= %indicator in food /% indicator in faeces
what are in vitro methods of measuring digestibility?
reproducing in the lab reactions which take place in the GIT, relative time consuming
uses samples of rumen/caeca fluid or a substitute to measure amount digested to generate digestibility or can measure gas released
what is MFN
metabolic faecal N
body supplies own N as insufficient from diet, therefore effecting results of digestibility as the N isn’t from the foodstuff
what are the values from digestibility trials called?
apparent digestibility coefficients, results obtained not 100% reliable
what are 6 factors affecting digestibility
food composition ration composition prep of food animal factors level of feed previous feedings
what has the greatest affect on digestibility?
crude fibre fraction
how does the preparation of food affect its digestibility?
anything that increases SA and breaks down fibrous outer full increases digestibility
how is dry matter determined
drying out sample 16 + hours, reweigh
what makes up the inorganic component of DM?
ash and minerals, high values indicate contamination
what are the organic components of DM
carbs, lipids, proteins and vitamins
how is the total N level measured?
Kjeldahl method
how is crude protein calculated?
N content X 6.25
what is crude fibre?
mainly plant structural carbs and some lignin, not commonly used as method not very repeatable
what are the 2 detergent methods of analysis?
acid detergent fibre
- can determine crude fibre and lignin content
neutral detergent fibre
- differs to acid one in it measures hemicellulose content
what is ether extract?
approximates true oil and fat content
what is a nitrogen free extract?
100- crude fibre%- moisture %- either extract =NFE
what are the 3 forms that minerals exist in food?
- metallic ions in solution (well absorbed)
- constituent of metallo-organic substances (poorly absorbed)
- constituents of insoluble substances (poorly absorbed)
conversion of insoluble to soluble affected by pH
how is starch and sugar measured?
sugar
colourmetrically after digestion
starch
after hydrolysis and polarimetric analyses
how are AA, FA and fat soluble vitamins measured?
chromatographically
what is gross energy?
a muffin in a hotdog suit
quantity of energy in chemical bonds
measured by converting food into heat and determining heat produced (bomb calorimetry)
what is digestible energy?
energy of food
=gross energy - energy contained in faeces for a unit of input
measured by bomb calorimetry
useful for horses
what is metabolisable energy?
= digestible energy - energy lost as urine and combustible gases
difficult to measure
useful for ruminants
what is net energy?
extent metabolic energy (ME) is utilised by the animal
how do you determine the biological value of a food?
% of N absorbed which is retained by the animal
measure of the proportion of food protein which can be metabolised by the animal
