Digest Ibility

7/23/2019 Digest Ibility

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Digestibility

Digestible part of foods or nutrients is the prportion which is absorbed

by the animal, which is not exreeted in the faeces.

Digestible compounds:

protein amino acids

starch glucose

fats fatty acids, monoglycerides

Calculation:digestible nutrient content = nutrient intake nutrient excretion in the

faeces

Can be expressed as a coefficient or a percentage.

apparent or true digestibility

The faeces contains not only the unabsorbed part of food, but also some

so called endogenous compounds erosion of epithelial cells, en!ymes

etc.".

true digestibility:correction with the endogenous compounds

apparent digestibility :without correction with the endogenous materials


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nutrient consumed nutrient excreted in faeces

apparent digestibility = ############################################################### $" nutrient consumed

nutrient consumed nutrient excreted in faeces endogenous losses"true digestibility =################################################################################################# $"

nutrient consumed

Taking into account endogenous losses is important mostly in the case ofproteins and amino acids.

%ndogenous losses in the faeces:

epithelial cells of the intestine

en!ymes

products of bacterial fermentation


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Ileal or faecal digestibility

absorption in the small intestine degradation in the large intestine

A

100%

B

&'$

&($

ileal digesta contains:

A 25%B 30%

'$

)($

faecal digesta contains:

A 20%B 20%

Microbial activity in the hind gt can modify the nabsorbed

part of the ntrients and so the accracy of faecal digestibility!

ileal digestibility

*: &'$

+: &($

faecal digestibility

*: ($+: ($


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Determination of digestibility

*nimal experiments

a! "imple digestibility trial#if the feedstff cold be given tothe animals as the sole item of diet$ corn ith poltry

species$ hay for rminants&

preliminary period e'perimental period

-n the experimental period the feed consumed and the

faeces excreted must be measured exactly.

C#%

Digestibility coefficient $" = ############## x )((

C

where C = consumed nutrient content

% = excreted nutrient in faeces


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b! (ifference method #if the feedstff can not be given to the animal alone$

otherise it can case digestive distrbances) for e'ample cereal grains ith

rminants&


Digestibility coefficient $"= *#+ x b"

dwhere *= the common digestibility coefficient of the two feedstuffs

+= the digestibility of the accompanying feedstuff

b= ratio of the accompanying feedstuff

d= ratio of the test feedstuff


accompanying feedstff

accompanying feedstff * test feedstff


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preliminary period test period

rminants

sbstantial change in the feed 20 +,10

small change in tghe feed 10 +,10

pig

feeding cereal grains - 5

The length of digestibility trials

/he ratio of the test feedstff in the ratio #%& nmber of animals

rminants100502525

3.+

pig10050

3+

poltry10050

3+,

The animal number needed for digestibility trials


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c! Indicator method if e do not have special balance cages$

or total collection is not possible$ lie ileal sampling$

taing representative e'creta samples enoghindicators$ marers:

indigestible natral componds of the feed #lignin$ acid insolble

ash #silica&$

pl! r243 /i42

reirements against indicators:6 shold not be absorbed6 shold not distrb digestion of ntrients6 its transit time shold be steady6 its analysis shold be accrate

6 cold be incorporated into the test diet homogenosly *#+ x -t-b"Digestibility coefficient $"= #########################

*

where *= nutrient content of the feed

+= nutrient content of the faeces

-t= indicator content of the feed-b= indicator content of the faeces


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d. Continuous digestibility trial6 /e can use it for measuring the digestibility of herbage eaten by gra!ing animals.

6 0ignin or acid insoluble ash can be used as an indicator.6 -f the fibre and lignin content of a grass increase, it decreases the digestibility of

starch, fat and protein. 1o, the optimal gra!ing or cutting time can be determined.

6 2epresentati3e faces samples are collected after se3eral days and the nutrient andlignin content of both grass and faeces are determined.

e. 0aboratory methods of estimating digestibility -t is not so laborious and expensi3e

Digestion of protein in non ruminants can be determined after incubation 45oC"

the feed with pepsin and hydrochloric acid, or by digesti3e tract secretion

collected 3ia cannulae.

7-n the case of ruminants the finely ground sample of feed is incubated for 6 hours

with rumen li7uor in a tube under anaerobic conditions. *fter that the bacteria arekilled by acidifying with hydrochloric acid and then digested with pepsin for a

further 6 hours. The insoluble residue is filtered off, and its nutrient content is

subtracted from the nutrient content of the feed. The difference is the digestible part.


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8actors affecting digestibility :

a. *nimal factors :

species different digesti3e characteristics"

breednot significant differences exist between different

breeds of the same species, indi3idual differences are

sometimes bigger"

age of the animalyoung animals can not digest the

feeds as efficient as the adults, because of the less

en!yme secretion"

become accustomed to a feedchanging feedcomposition suddenly decreases digestibility mostly in

the case of ruminants"


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b. 8ood factors:

fibre content if the fibre content is too high, it effectsnegati3ely on the digestibility of the other nutrients"

carbohydrates sugar content of the food can causedepression in the rumen fermentation"

enzyme supplementation of the foodit can be ad3antageousin young animals or against anti#nutrit93 factors"

the amount of food eatenif the amount of consumed foodincrease, the transit time of digesta will be 7uicker, so thedigestibility of nutrients will be less.

preparation of foods grinding, pelleting, heat and steamtreatment of soybean, boiling of potato etc. helps indigestion"

anti-nutritive compounds of feedstuffs trypsin inhibitors,solanin, glucans and xylans etc. decrease digestion"


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). Calculate the digestibility coefficients of alfalfa hay,

which was determined with sheep. *nimals were fed ),'

kg hayday, their excreted ), kg faecesday.

alfalfa hay

gkg"

faeces

gkg"

digestibility

coefficient

#%&

digestible

ntrient

content

#g8g&

dry matter -5 2.0

crude protein 200 -0

crude fat 25 .

crude fibre 2-2 #free

extract

.0. .


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;. Calculate the protein digestibility coefficient of barley protein. *

difference trial was carried out with sheep.

*s an accompanying feed )kg hay per day was fed in the

first experiment. The daily faeces excretion was ).; kg. The crude

protein content of the hay and faeces were ))' and 6; gkgrespecti3ely.

-n a second experiment beside ) kg hay (.' kg barley

was fed. The crude protein content of the barley was ))< gkg. -n

this experiment the daily amount of faeces was ).' kg, its protein

content was 6$.

4. Calculate the fat digestibility coefficient and digestible fat

content of a broiler diet .

*ccording to the results of an indicator trial the fat and Cr;4

content of the diet were

Digest Ibility

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