Maintenance Requirements
An animal is in a state of maintenance when its body composition remains constant:
• All obligatory losses are met (e.g., tissue turnover from muscles, gut and skin, hair and wool)
• Losses from urine and faeces replaced
• No net change in tissue mass
• No product such as milk or wool included
• No extra tissue growth such as products of conception
The purpose of maintenance diet is to prevent a drain on body tissues No net anabolism/catabolism of tissues Maintenance Diet
Factors Contributing to Maintenance Energy and Protein Maintenance
– Basal/fasting metabolic rate
– Homeothermy (housed/weather/climate)
– Activity (foraging/grazing v. hand fed)
– Diet type and quality
– Level of production
Basal Energy Requirements
Defined as the energy required only for those functions immediately necessary for life All food consumed ultimately leaves the animal as heat or waste No net product No work done on the environment
Fasting Metabolism
In a fasting animal the quantity of heat produced is equal to the energy of the tissue catabolised and when measured under specific conditions is known as the animals fasting metabolism Fasting metabolism is a more practical measure of maintenance energy requirements for animals than basal metabolic rate largely due to voluntary muscle activity that cannot be controlled in experiments
Homeothermy
Mammals and birds are homeotherms
• Energy expended to maintain core body temperature
• Rate of heat loss/gain dependant upon
• Difference between body temperature and environmental temperature
• Insulative properties of skin and coat
• Humidity
• Air flow
• Radiative/conductive loads (e.g., solar, heat sources/sinks)
Animals responds to change in heat load by:
• Selective adjustments to temperature gradient in and around body
• Altering blood flow to skin
• Changes to skin or hair
• Panting/sweating (evaporative heat loss)
• Removal of heat from blood flowing to extremities (cold) Lower critical temperature reached where heat production contributes to maintenance energy to maintain core temperature:
• Uncoupled energy production (e.g., brown fat and futile cycling)
• Shivering (muscle derived heat production)
Energy Associated with Diet Type and Quality Efficiency of use of energy from feeds varies with:
• Physiological age of animal (suckling, growing, mature)
• Physiological state (dry, pregnant, lactating)
• Energy content of feed (high energy v. low energy)
• Processing of feed (whole v. cracked v. pelleted grain; long v. chopped forages)
• Composition (quality) of feed
Energy Associated with Activity (Ruminants)
• Walking (foraging/grazing v. hand fed)
• Horizontal (2.6 kJ/km per kg liveweight)
• Vertical (28 kJ/kg per kg liveweight)
• Standing v. lying down (10 kJ/day per kg liveweight)
• Eating, i.e., prehension and chewing (2.5 kJ/hour per kg liveweight)
• Ruminating (2 kJ/hour per kg liveweight)
Rumen Function
• Reticulo‐rumen: Mixing, rumination, fermentation, particle separation, absorption of water, volatile fatty acids and exchange of salts
• Omasum: Absorption water, volatile fatty acids and exchange of salts
• Abomasum (true stomach): Normal digestive processes
Maintenance Energy Requirement Increases with Level of Production
• Productive animals have a higher maintenance energy requirement
• Relates to factors such as increased:
• Gut tissue and accessory digestive organ size and activity
• Energy cost of processing feed in gut (chewing, gut motility, secretions)
• Can be estimated as a fraction of energy intake (~10% of energy used for productive requirements)
Protein Requirements for Maintenance Animal placed on a nitrogen free diet continues to:
• Excrete nitrogen in urine and faeces
• Shed hair and skin cells This represents a net loss of protein from the body This protein must be replaced to ensure no net catabolism of tissues Losses increase with increasing feed intake (level of production) The amount of protein required to ensure no net catabolism of tissues represents the maintenance protein requirements of the animal
Protein Losses
Faecal nitrogen:
• Cell residues
• Enzyme residues
• Microbial residues
Urinary nitrogen:
• Creatinine from muscle activity (creatine to creatinine)
• Urea from amino acid turnover
Hair, wool and skin (scurf)
• Cell residues
Protein Turnover
• Proteins in body tissues not static
• Proteins constantly broken down into amino acids and replaced
• Amino acids enter the body pool
• Amino acids are recycled but process is not completely efficient Protein turnover time of:
• Hours to days for liver and intestines
• Days to weeks for muscle tissue
• Months to weeks for nerve tissue and bones
Amino acids are recycled
• Process efficient, but not completely so
• Catabolism of amino acids yields substrate for other synthetic process (e.g., gluconeogenesis) and amino groups
• Amino groups are converted to urea and excreted in urine
Growth and Development
Most common measure of growth is liveweight change Liveweight change includes:
• Body tissue (muscle, bone, fat, nerves)
• Extracellular fluid (blood plasma, lymph, interstitial fluid, cerebrospinal fluid)
• Intestinal contents
• Products of conception (foetus, placental tissues, amniotic fluid) Developmental changes in body proportions change the animal’s nutrient requirements
Changes in Nutrient Requirements with Growth and Development
With age the proportion of:
• Protein decreases (small amount)
• Fat increases
• Water in the carcass decreases
These changes lead to a rise in energy content per unit gain
Question
An animal is in a state of maintenance when its body composition remains constant:
• All obligatory losses are met (e.g., tissue turnover from muscles, gut and skin, hair and wool)
• Losses from urine and faeces replaced
• No net change in tissue mass
• No product such as milk or wool included
• No extra tissue growth such as products of conception
The purpose of maintenance diet is to prevent a drain on body tissues No net anabolism/catabolism of tissues Maintenance Diet
Factors Contributing to Maintenance Energy and Protein Maintenance
– Basal/fasting metabolic rate
– Homeothermy (housed/weather/climate)
– Activity (foraging/grazing v. hand fed)
– Diet type and quality
– Level of production
Basal Energy Requirements
Defined as the energy required only for those functions immediately necessary for life All food consumed ultimately leaves the animal as heat or waste No net product No work done on the environment
Fasting Metabolism
In a fasting animal the quantity of heat produced is equal to the energy of the tissue catabolised and when measured under specific conditions is known as the animals fasting metabolism Fasting metabolism is a more practical measure of maintenance energy requirements for animals than basal metabolic rate largely due to voluntary muscle activity that cannot be controlled in experiments
Homeothermy
Mammals and birds are homeotherms
• Energy expended to maintain core body temperature
• Rate of heat loss/gain dependant upon
• Difference between body temperature and environmental temperature
• Insulative properties of skin and coat
• Humidity
• Air flow
• Radiative/conductive loads (e.g., solar, heat sources/sinks)
Animals responds to change in heat load by:
• Selective adjustments to temperature gradient in and around body
• Altering blood flow to skin
• Changes to skin or hair
• Panting/sweating (evaporative heat loss)
• Removal of heat from blood flowing to extremities (cold) Lower critical temperature reached where heat production contributes to maintenance energy to maintain core temperature:
• Uncoupled energy production (e.g., brown fat and futile cycling)
• Shivering (muscle derived heat production)
Energy Associated with Diet Type and Quality Efficiency of use of energy from feeds varies with:
• Physiological age of animal (suckling, growing, mature)
• Physiological state (dry, pregnant, lactating)
• Energy content of feed (high energy v. low energy)
• Processing of feed (whole v. cracked v. pelleted grain; long v. chopped forages)
• Composition (quality) of feed
Energy Associated with Activity (Ruminants)
• Walking (foraging/grazing v. hand fed)
• Horizontal (2.6 kJ/km per kg liveweight)
• Vertical (28 kJ/kg per kg liveweight)
• Standing v. lying down (10 kJ/day per kg liveweight)
• Eating, i.e., prehension and chewing (2.5 kJ/hour per kg liveweight)
• Ruminating (2 kJ/hour per kg liveweight)
Rumen Function
• Reticulo‐rumen: Mixing, rumination, fermentation, particle separation, absorption of water, volatile fatty acids and exchange of salts
• Omasum: Absorption water, volatile fatty acids and exchange of salts
• Abomasum (true stomach): Normal digestive processes
Maintenance Energy Requirement Increases with Level of Production
• Productive animals have a higher maintenance energy requirement
• Relates to factors such as increased:
• Gut tissue and accessory digestive organ size and activity
• Energy cost of processing feed in gut (chewing, gut motility, secretions)
• Can be estimated as a fraction of energy intake (~10% of energy used for productive requirements)
Protein Requirements for Maintenance Animal placed on a nitrogen free diet continues to:
• Excrete nitrogen in urine and faeces
• Shed hair and skin cells This represents a net loss of protein from the body This protein must be replaced to ensure no net catabolism of tissues Losses increase with increasing feed intake (level of production) The amount of protein required to ensure no net catabolism of tissues represents the maintenance protein requirements of the animal
Protein Losses
Faecal nitrogen:
• Cell residues
• Enzyme residues
• Microbial residues
Urinary nitrogen:
• Creatinine from muscle activity (creatine to creatinine)
• Urea from amino acid turnover
Hair, wool and skin (scurf)
• Cell residues
Protein Turnover
• Proteins in body tissues not static
• Proteins constantly broken down into amino acids and replaced
• Amino acids enter the body pool
• Amino acids are recycled but process is not completely efficient Protein turnover time of:
• Hours to days for liver and intestines
• Days to weeks for muscle tissue
• Months to weeks for nerve tissue and bones
Amino acids are recycled
• Process efficient, but not completely so
• Catabolism of amino acids yields substrate for other synthetic process (e.g., gluconeogenesis) and amino groups
• Amino groups are converted to urea and excreted in urine
Growth and Development
Most common measure of growth is liveweight change Liveweight change includes:
• Body tissue (muscle, bone, fat, nerves)
• Extracellular fluid (blood plasma, lymph, interstitial fluid, cerebrospinal fluid)
• Intestinal contents
• Products of conception (foetus, placental tissues, amniotic fluid) Developmental changes in body proportions change the animal’s nutrient requirements
Changes in Nutrient Requirements with Growth and Development
With age the proportion of:
• Protein decreases (small amount)
• Fat increases
• Water in the carcass decreases
These changes lead to a rise in energy content per unit gain
Question
- Define what is meant by meeting an animals requirements for maintenance in a diet
- Describe the key factors that determine maintenance energy and protein requirements
- Describe the key factors that determine protein and energy requirements for growth