Animal nutrition - feed evaluation Flashcards
Digested feed is deemed to be that which
is decomposed and absorbed by the body and used for metabolic processes.
Digestibility of feeds is commonly expressed in terms of
dry matter and as a coefficient or a percentage -> 0.65 or 65%
Methods for determining digestibility are (4)
– in vivo method -> experiments with animals
– in vitro method -> experiments in the laboratory
– nylon bag method (in sacco, also in situ) -> experiments with fistulated animals
– indicator method -> experiments with animals
What is in Sacco digestibility?
Refers to in sacco which is equivalent to in situ.
In-sacco method is a direct method of calculating digestibility by measuring disappearance of defined feed stuff from undegradable porous bag (polyester, nylon or dacron).
Nylon bags with test feed are inserted into the rumen via the rumen fistula.
After incubation the degradability (digestibility) in the rumen can be found through the difference between the nutrient content of the initial feed and the feed remaining in the bag.
In vivo method of digestibility determination is the most
accurate, but labour-intensive.
Feed nutrient digestibility is determined at what level
the maintenance feeding level.
– results of the various tests are comparable
A digestibility trial can be divided as follows: (3)
– adaptation period -> 10-12 days, animals become accustomed to the experimental ration to ensure that their digestive tract is clear of previous feed residues
– preliminary period –> 10 days, feed intake is measured
– collection period -> 10-12 days, feed intake and faecal output are recorded daily
The digestibility is calculated as the difference between
eaten and excreted nutrients in faeces.
Nutrients digestibilities found in digestibility experiments should be regarded as
apparent.
This means that the process is not perfect and nutrients of endogenous origin cannot be separated by Weende analysis. (endogenous nitrogen especially)
In practice, to account for this discrepencies in measurements, apparent digestibility coefficients are used.
in monogastric animals the results of the In vitro method are satisfactory only for
the determination of protein digestibility
– in ruminant animals it is suited well for the determination of digestibility
In vitro experimental results are somewhat better/higher than
the in vivo experiment results.
– this is so because we cannot artificially create all the conditions that occur in the animal
the Indicator method Can be used when it is
is impractical to measure either feed intake or faecal output
exactly, directly
what is the Indicator method
An inert substance, which is indigestible in the animal body is added to the feed ration (Chromium(III) oxide, Silicon dioxide, indigestible NDF, ADF, acid insoluble ash) that is then measured from the output.
The digestibility of a feed is closely related to its
chemical composition
the chemical composition of barley, even in
different varieties, is
quite stable, and therefore the nutritive factors’ digestibility differences between the different varieties are small
the digestibility of cell wall substances depends on
the ratio of
the cellulose to lignin
The digestibility of a feed is influenced not only by its
own composition but also by
the composition of other feeds consumed with it
– these associative effects may be positive or negative
protein feed fed together with straw may enhance
the microbial activity, and therefore the digestibility of the straw
a high amount of rumen fermentable starch reduces ruminal pH and therefore inhibits the activity of
cellulolytic bacteria and reduces fibre digestibility
duration of digestion is also important
– if the ration contains more fibre then
the feed stays in the digestive tract for a longer time and digests better
it is subject to action of digestive enzymes for a longer time
if the ration contains less fibre then this increases the chyme what
passage rate and the digestibility is lower
-> the duration of action of the digestive enzymes is less
In order to ensure maximum digestibility of grains
they must be
ground as finely as possible for monogastric animals
can be crushed for ruminants ->
in most cases this is sufficient, except for maize, wheat/rye/triticale (are durum grains)
NB! unground or uncrushed grains pass through the
digestive tract and remain undigested
what are the only type of seeds that can be digested without the need for crushing_
cottonseeds
Chopped, ground or granulated forages contain the same amount of nutrients as the grass from which they made, but the
nutrient (fibre) digestibility is lower
feed remains for a shorter time in the digestive tract, the effect of enzymes is reduced. ground hay has 20% less digestibility because of its faster mmovement through the GI tract
NorFor system is
a semi-mechanistic feed evaluation system for cattle, which is used by advisors in Denmark, Iceland, Norway and Sweden.
rumen load index, structure unit
To increase cereal straw digestibility it is treated for 2…3 weeks before feeding with
concentrated NaOH
sodium hydroxide / lye
straw digestibility increases 40% → 60…65%
Feed heat treatment does not directly improve digestibility, but
inactivates factors such as trypsin inhibitor (soybean)
name 2 synthetic enzymes that may be added to a ration to increase digestibility
β-glucanase (for carbs)
phytase (cleaves phytates)
phytate/phytic acid is the non-complexed form of phytin the anti-nutrtional compound.
phytic acid can readily bind to mineral cations.
protein digestibility is higher in monogastric than in
ruminant animals
