4. Digestibilty

Question 1

Feed utilisation

Answer 1

simple chemical analysis of feedstuffs not enough
a large and variable component of feedstuffs is not available to the animal
largest and most variable component of this loss is in the faeces
digestibility measures the proportion of a given feed constituent that is not excreted in the faeces
the fraction of the feed that is absorbed from the GI tract

Question 2

Digestibility %

Answer 2

100-indigestibility

Question 3

Determination of digestibility

Answer 3

1. total faecal collection
2. use of indicators
   indigestible, unabsorbable, uniform rate of passage, no pharmalogical effect, readily analysable in feed and faeces
   Principle: undigestible component has x1 concentration in diet DM
   undigestible component has x2 concentration in faecal DM
   increase in concentration in faeces as digestible DM now gone
   increase in concentration is directly proportional to feed disappearance in GI tract or digestibility

Question 4

Concentrations of digestible nutrients: DOMD, DE

Answer 4

digestible organic matter in the dry matter DOMD
-a measure of the concentration of digestible energy yielding nutrients in the feed DM
-domd or d value used extensively in ruminant nutrition: silage analysis, concentrate feed analysis
Digestible energy concentration DE, pig, horse
-a more accurate estimate of concentration of digestible energy yielding nutrients in feeds

Question 5

Apparent vs True digestibility

Answer 5

Faeces contain more than undigested feed
micro organisms from GI tract: whole or part
endogenous secretions: GI tract cells; enzymes
undigested feed
Apparent : considers the entire faecal excretion as the indigestible amount
True : considers only the undigested feed as the indigestible amount
most important for protein, amino acids, minerals

Question 6

Factors affecting digestibility

Answer 6

Feed composition
fibre or cell wall
-NDF: cellulose, hemicellulose, lignin
-Digestibility very variable
Cell contents
-starch, sugars
-digestibility higher than fibre
Protein animal/vegetable
-true digestibility usually 85 to 100%
Concentrates have higher digestibility than forages

Question 7

Feed composition and Digestibility

Answer 7

fibre limited digestibility in dog and cat
digestibility of different fibre sources varies
Effect of lignin on cell wall fibre digestibility:
lignin reduces digestibility of cell wall components with which it is co-bonded: principally cellulose
lignin protects 2.5 to 3 times its weight of plant cell wall from digestion
ruminant concentrate feed OMD%= 87.9-2.58 x ADL%

Question 8

Chemical treatment of animal feed

Answer 8

advantage taken of chemicals which attack cell wall linkages
ammonia treatments of forages
sodium hydroxide treatment of grains
urea treatment of grains/ whole crop cereals
acid treatment of grains

Question 9

Physical treatment

Answer 9

rolling
grinding: reduces forage digestibility
crimping
horses and sheep no benefit, cattle and pigs benefit in total tract DMD

Question 10

Heat treatment

Answer 10

micronization, extrusion, roasting
advantages with some cereals for ruminants
may denature proteins in dog and cat foods
heat treatment causes gelatinization of starch which makes it more digestible for most animal species

Question 11

Companion animal feed ingredients

Answer 11

Soybean flour more digestible than soybean grits in dog diets
blended rice more digestible than whole rice in dog diets
finer material exposes more of the surface area to enzymes involved in digestion
high temperature drying can reduce the digestibility of meat and bone meal and poultry meal in dog and cat food diets
damages protein creates chemical alteration called maillard products less digestible
high temperature drying can reduce digestibility of farm animal protein sources such as distillers dried grains and grass meal

Question 12

Rate of passage and digestibility

Answer 12

extent of digestion: competing rates of digestion and passage
need time for maximum digestion
digestibility declines of up to 12% common in dairy cows
passage rate increases, diet digestibility declines
-increase feed intake
-pregnancy
-breed
-stress
-feed allergies

Question 13

Compartmental digestion Horses

Answer 13

horses
pre-caecal digestion of cereal starch
important for determination of starch load at caecum and colon
also in-situ or mobile nylon bag: naso-gastric tube: caecal cannula

Question 14

Compartmental digestion
Companion animals, pigs and ruminants

Answer 14

ileal digestibility of amino acids
ileal cannula
ileal-rectal anastomosis

Question 15

Compartmental digestion Ruminants

Answer 15

protein digestion in rumen: rumen degradability
needed to determine protein supply to rumen micro-organisms
requires fistulated animals: in-situ nylon bag
ruminal degradability estimates
-solubility of feed protein
-rate of protein disappearance for insoluble fraction
-rumen retention time
rumen degradability of protein
-standard rapeseed meal 71%
-rumen protectes rapeseed meal 35%

Question 16

Predicting digestibility

Answer 16

chemical analysis
-ruminants; horses; pigs; small animals
energy digestibility of dry dog food
-94-(4.04xCF%)
In-vitro digestibility assays
-rumen fluid: tillery and terry
-mix of enzymes: pepsin, cellulase, gammanase
-pigs: gastric, pancreatic, microbial enzymes; EFOS method
-dogs: multiple enzyme system
Gas production: gut contents or faecal innocula
-extent of digestion
-rate of digestion

Question 17

Near infrared reflectance spectroscopy NIRS

Answer 17

rapid technique
total tract digestibility, rate of digestion, protein degradability
extremely powerful best predictor
needs calibration
accuracy of prediction of total tract digestibility of ruminant feeds

Question 18

Whole barley DMD

Answer 18

53.3%