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Diet evaluation

Q: Principle of measuring digestibility

- digestibility of a diet, ingredient or nutrient is that part which is absorbed in the digestive tract - most simple way to determine -> quantifying dietary intake and faeces production and analyse the nutrients of interest in a representative sample of diet and feaces - the results are expressed as apparent faecal digestibility coefficient - ADC = Nutrient intake – nutrient output x 100 / Nutrient intake

Q: In fish faeces can be collected by various techniques that can be classified as follows

Methods that collect (separate) the faeces from the water Methods that collect faeces directly from the GIT (stripping, suction or sacrificing) Stripping could lead to contamination of the digesta

Q: Measuring digestibility in various sections of the tract

- by measuring digestibility in the various sections of the tract information on partial digestibility is recovered - digestion in the forestomach determines intestinal protein supply

Q: Validity of digestibility coefficients

- Volatide fatty acids resulting from fermentation in the hindgut are mostly absobred and the energy is utilized by the animal - this is why for the digestibility of other nutrients faecal digestibility is used - in poulty faeces and urine are excreted together making determining digestibility difficult - solutions include colostromy or the ileal sampling (slaughter technique)

Q: Endogenous protein secretion can be estimated to calculate the true digestibility

- Determine N secretion by a protein-free diet - Determine N secretion by feeding animals graded levels of protein - using labelled protein

Q: In situ/in sacco methods

- evaluates the rate of degradation of various diet components in the rumen by filling a nylon bag with small amounts of diet sample - from the decline in residue dry matter with time the rate of degradation of the diet components can be estimated

Q: Methods have been developed to measure the in vivo digestibility in laboratories

Tilly and Terry: estimates the apparent organic matter digestibility in ruminants enzymes : digestion is stimulated by the activity of hydrolytic enzymes to obtain information on protein digestibility in monogastrics physical methods: predicting chemical composition and digestibility by physical measurements like Near Infrared Spectroscopy cumulative gas production method: used to obtain insight in rumen fermentation of different feedstuffs

Q: Protein supply to the small intestine can be estimated as

- the sum of dietary protein escaping microbial degradation in the rumen: by nylon bag incubations. From the residues in the bags after the different incubation times a declining curve can be drawn - microbial protein synthesis in the rumen: Can be estimated from the ratio between the duodenal flow of a microbial marker and the concentration of that marker in isolated bacteria - intestinal digestion of dietary and microbial protein: protein evaluation systems assume a constant apparent absorption regardless of the protein origin

9 important questions on Diet evaluation

Principle of measuring digestibility

- digestibility of a diet, ingredient or nutrient is that part which is absorbed in the digestive tract
- most simple way to determine -> quantifying dietary intake and faeces production and analyse the nutrients of interest in a representative sample of diet and feaces
- the results are expressed as apparent faecal digestibility coefficient
- ADC = Nutrient intake – nutrient output x 100 / Nutrient intake

The ratio of marker to nutrient in the diet and in faeces is used to estimate the nutrient digestibility using the formula:

DCnutrient = 100 – ([M]diet/ [M]faeces) x ([N]faeces/[N]diet) x 100
In which:
DCnutrient = digestibility of nutrient [M]diet = concentration of marker in diet [M]faeces = concentration of marker in faeces
[N]diet = concentration of nutrient in diet [N]faeces = concentration of nutrient in faeces

In fish faeces can be collected by various techniques that can be classified as follows

Methods that collect (separate) the faeces from the water
Methods that collect faeces directly from the GIT (stripping, suction or sacrificing) Stripping could lead to contamination of the digesta

Measuring digestibility in various sections of the tract

- by measuring digestibility in the various sections of the tract information on partial digestibility is recovered
- digestion in the forestomach determines intestinal protein supply

Validity of digestibility coefficients

- Volatide fatty acids resulting from fermentation in the hindgut are mostly absobred and the energy is utilized by the animal
- this is why for the digestibility of other nutrients faecal digestibility is used
- in poulty faeces and urine are excreted together making determining digestibility difficult
- solutions include colostromy or the ileal sampling (slaughter technique)

Endogenous protein secretion can be estimated to calculate the true digestibility

- Determine N secretion by a protein-free diet
- Determine N secretion by feeding animals graded levels of protein
- using labelled protein

In situ/in sacco methods

- evaluates the rate of degradation of various diet components in the rumen by filling a nylon bag with small amounts of diet sample
- from the decline in residue dry matter with time the rate of degradation of the diet components can be estimated

Methods have been developed to measure the in vivo digestibility in laboratories

Tilly and Terry: estimates the apparent organic matter digestibility in ruminants
enzymes: digestion is stimulated by the activity of hydrolytic enzymes to obtain information on protein digestibility in monogastrics
physical methods: predicting chemical composition and digestibility by physical measurements like Near Infrared Spectroscopy
cumulative gas production method: used to obtain insight in rumen fermentation of different feedstuffs

Protein supply to the small intestine can be estimated as

- the sum of dietary protein escaping microbial degradation in the rumen: by nylon bag incubations. From the residues in the bags after the different incubation times a declining curve can be drawn
- microbial protein synthesis in the rumen: Can be estimated from the ratio between the duodenal flow of a microbial marker and the concentration of that marker in isolated bacteria
- intestinal digestion of dietary and microbial protein: protein evaluation systems assume a constant apparent absorption regardless of the protein origin

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The question on the page originate from the summary of the following study material:

Animal nutrition | 9780471903758 | Aron A Bondi

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Diet evaluation

9 important questions on Diet evaluation

Principle of measuring digestibility

The ratio of marker to nutrient in the diet and in faeces is used to estimate the nutrient digestibility using the formula:

In fish faeces can be collected by various techniques that can be classified as follows

Measuring digestibility in various sections of the tract

Validity of digestibility coefficients

Endogenous protein secretion can be estimated to calculate the true digestibility

In situ/in sacco methods

Methods have been developed to measure the in vivo digestibility in laboratories

Protein supply to the small intestine can be estimated as

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