Energy systems, digestibility Flashcards
What is digestible feed?
The portion of the feed which is not excreted in feces and is assumed to be absorbed by the animal.
How is digestibility usually estimated and expressed?
Estimated in DM basis.
Expressed as a coefficient or percentage.
What is the formula for DM digestibilty?
(consumed-excreted)/consumed
What is apparent digestibility?
An estimation = feed ingested - feces excreted
What is true digestibility?
True digestibility involves correction for endogenous losses.
What information do you need to determine true digestibility?
- Sloughed off intestinal cells
- Digestive secretions (enzymes, mucus)
- Microbial matter
Which is higher, true or apparent digestibility?
True is higher than apparent
Which digestibility is more difficult and costly to determine?
True digestibility.
What are the different ways to measure digestibility in vivo?
- Growth trials
- Direct (total collection)
- Difference (basal + test food)
- Regression
- Tracer or indicator
Which in vivo measurement of digestibility is the most accurate?
Direct (total collection)
What are in vitro methods of digestibility measurement?
- Digestion stimulation
- Gas production
What is the adaptation period for direct measurement of digestibility?
1-2 weeks
How is direct (total collecttion) measurement of digestibility done?
- Feed a known quantity to the animal at the same time every day.
- The amounts of food eaten should not vary from day to day.
- Collect total fecal output for 5-14 days (during diet feeding period).
- Chemical analysis of feed and feces.
- Apparent digestibility calculation.
What are the lab conditions for sheep and cattle digestibility studies?
- Metabolic crates or chambers
- Animals are fitted with strap-on canvas fecal collection bags
- Urinary catheters are placed to prevent the contamination of feces with urine
NOTE: lab conditions impact digestibility
When are tracers or indicators used?
When it is impossible to measure total intake and fecal output (ex. group feeding or grazing animals).
What are the characteristics of a tracer?
- Indigestible
- Non-absorbable
- Non-toxic
- Easy to analyze
How are tracer studies done?
- Known tracer amount and known feed amount are given.
- Collection of fecal samples for at least one week of marker feeding.
- The marker is given continuously during the trial period until it is stabilized in the feces.
What are internal markers/tracers?
- Lignin
- Acid insoluble ash (silica)
- N-alkanes
What are external markers/tracers?
- Cr2O3 (ruminants)
- TiO2 (pigs, poultry)
What are the pros of using a tracer?
- Total feces collection is not necessary.
- Total intake determination is not necessary.
- Easier, less labor.
What are the cons of using a tracer?
- Representative sampling is essential.
- Accurate estimation of nutrient or marker concentration is essential.
- It assumes complete excretion of the marker and hence the recovery of the marker determines accuracy.
What is the definition of in vitro measurement of digestibility?
Lab methods to simulate digestion by the animal.
How is in vitro measurement of digestibility used for non-ruminants?
Protein digestion is determined by digesting the feed in pepsin and HCl.
How is in vitro measurement of digestibility used for ruminants?
The feed is incubated with rumen fluid under anaerobic conditions. The bacteria are then killed by acidifying with HCl and digested in pepsin.
What temperature is rumen fluid incubated at?
39 C
How is digestibility in different GIT portions measured?
In situ - fistulated animals (surgical procedure)
What is digestibility more associated to, feed characteristics or animal factors?
More associated to feed characteristics.
What are animal factors that affect digestibility?
- Species
- Individual factors
- Level of feed intake
- Frequency of feed intake
- Age
- Adaptation to feed
- Infectious disease or parasites
How does age affect digestibility?
Better in adults since young animals have less enzyme secretion
How does changing feed affect digestibility?
Sudden changes in feed composition usually decreases digestibility.
Which has less variability in digestibility: grain or forage?
Grain is less variable due to a more constant composition.
What feed factor has the greatest impact on digestibility?
Fibre fraction
How does grain processing impact digestibility?
Increases digestibility
What are associative effects?
Interaction between nutrients in different ingredients resulting in higher or lower digestibility than expected for individual ingredients
What are positive associative effects in ruminants?
Increased fibre utilization after N supplementation in N-deficient forages and supplementation of roughages with small quantities of sugars (do not ask me what he means by this)
What are negative associative effects in ruminants?
- Concentrate supplementation in excess can reduce fibre utilization
- Excess fat supplementation reduces fibre digestion
(if u wanna know how its in the slides)
What is the definition of energy?
The potential to do work.
Is energy a nutrient?
NO, but it is a result of nutrient metabolism
What is a calorie?
The amount of energy as heat required to raise by 1°C the temp of 1 g of water at a pressure of 1 atmosphere
What is a general rule for livestock and energy requirements? (I FEEL LIKE THIS IS IMPORTANT)
Livestock eat to their energy requirements
What is gross energy?
Total energy in feed
What does gross energy not tell you?
Does not give any indication of energy availability to the animal (does not account for animal factors)
What is gross energy dependent on?
The proportion of fat, CHO and protein in the feed.
What is digestible energy?
DE = GE minus energy lost in feces
How much energy is lost to feces?
Feces are a major source of energy loss (10-80%)
What is used as the measure of energy supply for pigs and horses?
Digestible energy
How does ADF affect digestibility?
Decreases DE
What is total digestible nutrients (TDN)?
%TDN = DCP + DCF + DNFE + (DEE*2.25)
- DCP = digestible crude protein
- DCF = digestible crude fibre
- DNFE = digestible nitrogen-free extract
- DEE = digestible ether extract (fat)
What is metabolizable energy?
ME = DE – (energy loss in urine + gas production)
What is a better estimate of energy in feed available to the animal?
Metabolizable energy
What is net energy?
NE = ME – heat lost during digestion process (Heat Increment, HI)
energy from feed retained and absorbed by the animal, fraction of total energy utilized for maintenance, growth and production
How do you calculate the efficiency of ME utilization?
NE = ME × k, where k represents the efficiency in conversion of energy substrates to ATP
What do you need to estimate in order to know NE?
heat loss
How is heat loss estimated?
Direct / indirect calorimetry
What is indirect calorimetry?
Respiration chambers
What factors affect energy requirements?
- Body weight
- Growth
- Age (life / production stage)
- Sex (M>F); castration/spaying
- Gestation / physiological stage
- 3/3rd pregnancy = higher energy requirement
- Disease = higher energy demands (?)
- Lactation (or egg or wool production)
0 Exercise (race horses, sled dogs, grazing large pastures) - Environment: temperature, wind, mud, condition of hair coat
What are energy systems?
Abstract scientific-based system (equations) to quantify, estimate and predict requirements and how to satisfy them with feed provided to the animal
What is usually the main limiting factor in animal production?
Energy
What is the main limitation for energy systems?
Requires accurate laboratory methods for predicting the energy content of foods from their characteristics
ME supplied as ____ is used more efficiently than ME supplied as ____
ME supplied as fat is used more efficiently than ME supplied as carbohydrate or protein
Energy systems for ___ and ___ are simpler than those for ruminants and herbivores
Energy systems for pigs and poultry are simpler than those for ruminants and herbivores
What energy system is used for dairy?
NE
What energy system is used for beef?
NEm (breeding cows) and NEm+NEg for growing/fattening
What energy system is used for swine?
NE system (NEm+NEg)
What energy system is used for poultry?
ME system
What energy system is used for horses?
DE (UK & US) and NE (France) system
What energy system is used for companion animals?
ME system
