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
crude fibre digestibility is higher in ruminant than in
monogastric animals
grain digestibility is somewhat higher in sheep than in
cattle
digestibility of lower quality forages is somewhat
higher in cattle than in
sheep
Feeding level is assessed by the
feeding level unit
The feeding level unit shows
how many times the amount of feeds is fed to the animal above the maintenance level
– e.g. if a 500kg cow is fed 225MJ ME per day, of which the maintenance requirement is 50MJ, then the
feeding level exceeding maintenance is 225 / 50 =
4.5 times
The feeding level unit should be how much in growing and fattening ruminants?
growing and fattening animals 2.0-3.0 times above
maintenance
The feeding level unit should be how much in lactating ruminants?
lactating animals 3.0-5.0 times
The feeding level unit should be how much in poultry?
poultry 2.0-3.0 times
The feeding level unit should be how much in growing pigs?
growing pigs 3.0-4.0 times
The feeding level unit should be how much in suckling sows?
▪ suckling sows 4.0-6.0 times
It has been shown that the digestibility of feeds
decreases for each
feeding level unit
– for high-fibre rations (hay, silage, grazed grass) increasing the level of feeding by one unit reduces the digestibility of the ration by 0.01-0.02 units
– for mixed rations (roughage + concentrate), and those
containing smaller particles, the reduction in digestibility
is 0.02-0.03 per one unit feeding level increase
typical dairy cow ration DM digestibility is 0.75, but
if the level of feeding is three times over maintenance
then the digestibility will be
reduced
▪ 0.75 - (3 x 0.02) = 0.69 (75% -> 69%)
the greatest reductions in digestibility with increasing
feeding level occur with
ground and pelleted forages, 0.05 digestibility units for one feeding level unit
hay unit made up by whom when and what is it?
Hay unit described by A. von Thaer in 1810, how much of meadow hay is needed to replace one unit of a reference feed without any change in production, based on fat deposition ability of fattening oxen
arbohydrate unit combined what back in 1850-?
Weende system of feed analysis (1850-60), digestibility
experiments, carbohydrate unit which combines digestible protein, fat and carbohydrates into one number
Total digestible nutrients (TDN) is another term for what
carbohydrate unit which combines digestible protein, fat and carbohydrates into one number
Kellner’s starch equivalent system was
used mainly in Europe as the basis of practical rationing systems until the 1970s
Feed unit, was used in
Scandinavia in 1880, based on milk production ability of dairy cows, equal to 1kg of concentrate
Scandinavian (barley) feed unit in 1915, equals
1kg of barley
Soviet (oats) feed unit, developed in 1922-23, based on
Kellner’s starch equivalent system (1 unit = 0.6 starch equivalent)
The barley feed unit estimates feeds somewhat
higher than the
oat feed unit (1 barley FU = 1.2 oats FU)
– nutritional value is higher in barley than in oats
When in the 1960-70s, British K. L. Blaxter, published a book The energy metabolism of ruminants nutritional value of feeds was based on:
– gross energy (GE)
– digestible energy (DE)
– metabolisable energy (ME)
gross energy (GE) =
combustion heat of organic matter
digestible energy (DE) is the energy
saved in digested organic matter
= gross energy (GE) – faeces energy
metabolisable energy (ME) is the energy of
the absorbed nutrients from feed
= digestible energy (DE) – (urine + gases energy)
caveat is that ME also contains urine energy; urine is a metabolism residue, which is formed from absorbed substances
net energy is the energy that
the animal uses for the functioning of internal organs (except for digestion), and muscles during sleep [maintenance], or which is excreted in the form of production
net energy =
NE = metabolisable energy – heat increment
▪ heat of biosynthesis (related to production) and
▪ active heat (related to maintenance)
Net energy can be divided into
maintenance (NEm) and production energy
-> gain (NEg), milk production (NEL)
The organism gets the necessary energy to catalyse
their biochemical processes from
ATP energy stored in macroergic bonds
Decayed 1 mole of ATP gives
52 kJ of energy
In the organism the ATP molecule forms and decays
continuously
– for example: in human body ATP circulates about
1,000 times in 24h
Crude protein =
Nitrogen x 6,25
Ideal protein is
a balanced protein with reference to the essential AAs, according to the species and gender and age group
in the body there is neither a deficiency nor a surplus of
essential amino acids
In growing pigs the amount of ideal protein (EAAs)
increases with the growth of pigs, but the ratio of
(essential) AAs must remain the same
The first limiting AA in the pig ration is
lysine
and if its content in the ration is 50 g/kg, the ideal protein content is 0.7 (50/70) or 700g in kg protein.
Protein degradability in the rumen Is used as a separate system in US and Canadian advisory systems but in estonia
it is a part of the metabolisable protein (AAT) system
The rule is: if milk production is higher, then the
ration must contain more
rumen undegradable protein
– for example: a 600kg dairy cow ration must contain
rumen undegradable protein at:
▪ 25 kg milk production 27%
▪ 35 kg 36%
▪ 45 kg 41%
Under the term „metabolisable protein“ we mean
the sum of AAs truly absorbed in the small intestine, which are also used by the host animal, and originate from
– microbial protein and
– rumen undegradable and digestible (in the small
intestine) protein
Protein balance value (PBV) shows
the difference between rumen degradable protein & potentially synthesised microbial protein in the rumen.
EPD stands for
effective protein degradability
which method is the most labour intensive?
A. In vivo method
B. In vitro method
C. Indicator method
A. In vivo method
the digestibility is better when …
A. the chymus flows quicker through digestive tract
B. the chymus flows slower through digestive tract
B. the chymus flows slower through digestive tract
which energy evaluation system is used in the Estonia?
A. Oats feed unit
B. Metabolisable energy
C. Neto energy
B. Metabolisable energy
which protein evaluation system is used for dairy cows in the Estonia?
A. Ideal protein
B. Protein degradability in the rumen
C. Metabolisable protein
C. Metabolisable protein
