Protein Nutrition of Dogs

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Protein Nutrition of Dogs
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Protein

• Basic unit amino acid
• Held together by peptide bond to form protein
  chains
• Functions
• Structural (hair, skin, tendons, ligament,
  cartilage)
• Contractile proteins (myosin, actin)
• Enzymes (pepsin, insulin, etc.)
• Hormones
• Carriers of nutrients in blood (hemoglobin,
  plasma proteins)

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Proteins
Protein (2 AA joined by peptide bond between ?
carboxyl and ? amino group
Amino Acid (AA)
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Protein

• Amount in body NOT static
• Constant state of degradation and synthesis
• Tissues vary in rate of turnoverthey are all
  eventually broken down (catabolized) and replaced
• Maintenance state
• Thus, physiological states other than maintenance
  require additional protein
• Reproduction, growth, lactation

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Dietary Protein

• Serves several important functions
• Source of essential amino acids
• Used for protein synthesis in growth and repair
• Used as principle source of N for the body
• Source of energy
• GE 5.65 kcal/g
• Has flavor! Increases palatability
• When cooked with CHO and fat
• As protein ? palatability ?

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Essential AA

• PVT TIM HALL (KNOW!)

• Phenylalanine
• Valine
• Threonine
• Tryptophan
• Isoleucine
• Methionine

• Histidine
• Arginine
• Lysine
• Leucine

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Nitrogen

• Essential for synthesis of nonessential AA
• Essential for synthesis of other
  nitrogen-containing compounds
• Nucleic acids, purines, pyrimidines,
  neurotransmitter substances

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Excess Nitrogen

• Animals unable to store
• Used for energy
• Converted to glycogen or fat and stored

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Protein Quality

• Definition balance of bioavailable AA in a feed
  ingredient relative to animals AA requirement

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Protein Quality

• High quality highly digestible, contain all of
  EAA in proper amounts relative to reqt.
• Low quality low digestibility, limiting in one
  or more EAA
• Higher the quality the lower the inclusion rate
  to meet reqts.

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Limiting AA

• The essential AA that is in the greatest deficit
  in a protein source
• This will be the AA that will LIMIT the bodys
  ability to use that protein source

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Predicting Protein Quality

• Chemical Score
• Compares AA composition of protein source to the
  gold standard egg protein
• Formula limiting AA/ of that AA in egg
• Essential AA Index (EAAI)
• Modified chemical score
• Measures contribution that protein source makes
  to all EAA, rather than only the one in the
  greatest deficit
• Formula AA/ AA in egg (summed for all EAA)

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Predicting Protein Quality

• Total Essential AA content (E/T)
• Proportion of total N in protein source that is
  contributed by EAA
• Formula Amt N from EAA/ Amt of total N
• CS and EAAI indicate quality of protein sources
  AA profile, E/T measures total quantity of EAA in
  protein source

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Protein Quality

• Estimations of protein quality from AA
  composition are helpful in accessing protein
  quality when different combinations of protein
  sources are used in food
• Provides no information regarding the
  digestibility of protein or availability of AA
• Why??

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Heat Damaged Proteins

• Bioavailability the degree to which an ingested
  nutrient is absorbed in a form that can be
  utilized
• Includes
• Digestion
• Absorption
• Utilization
• Changes in protein structure will change protein
  availability, not presence of measurable N

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Heat Damaged Proteins

• Maillard Reaction (Browning Reaction)
• Caused by excess heat cooking, drying, improper
  storage
• Protein-CHO complex formed
• Protein is still there, just unavailable to animal

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Maillard Reaction
HCO CHOH CHOH
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Maillard Reaction
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Determination of Protein Bioavailability

• Protein efficiency ratio (PER)
• Simple, very common
• Value indicates ability of protein source to be
  converted to tissue in growing animal
• ASSUMPTION weight gain nitrogen retention
• True in rats, but in dogs???
• Any factor that affects growth rate during study
  will affect PER
• Regardless if it was related to protein quality

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Determination of Protein Bioavailability

• Biological Value (BV)
• Time consuming, expensive
• More accurate measures of protein quality
• Efficiency with which a protein furnishes the
  required amounts of essential amino acids needed
  for productive body functions
• Used to index or rank protein quality
• Does not account for digestibility

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Determination of Protein Bioavailability

• Net Protein Utilization (NPU)
• Time consuming, expensive
• More accurate measures of protein quality
• Accounts for digestibility
• Product of protein sources BV and digestibility
• Measures proportion of consumed protein that is
  retained in the body
• Thus, highly digestible protein BV NPU, BUT
  lowly digestible protein NPU lt BV

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Protein Requirement

• Minimum intake of dietary protein that promotes
  optimal performance
• Evaluated based on nitrogen balance and growth
  rate
• N balance N intake N output (feces urine)

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N losses

• Feces
• Unabsorbed dietary protein
• Endogenous N sources
• Sloughed intestinal cells
• Sloughed microbial cells
• Spent enzymes
• Mucin
• Urine
• Urea endproduct of protein breakdown

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Nitrogen Balance
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Protein Deficiency in Dogs

• Commonly occurs with energy deficiency
• Protein/calorie malnutrition
• Uncommon in companion animals fed commercial pet
  foods
• Usually occurs when pet owners economize by
  feeding poor quality rations
• Lactation, pregnancy (high nutrient needs)

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Protein Excess in Dogs

• Excess protein
• Used for energy (negative energy balance)
• Metabolized to fat for storage (positive energy
  balance)
• Excreted in urine as urea
• Huge excesses implicated in development of
  chronic renal disease

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Factors affecting Protein Requirements

• Digestibility
• Premium foods 80-90
• Generics less than 75
• Protein Quality
• Higher BV, less need to meet EAA reqts.

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Factors affecting Protein Requirements

• Caloric density of diet
• Energy need is met first, so if enough
  non-protein energy-containing nutrients (fat,
  CHO) to meet E reqt., then AA used for other
  functions
• Remember, if energy concentration ? total
  concentration of AA must ?
• Lower intakes at higher energy concentrations
• Protein must contribute a higher proportion of
  diet so animal can meet total protein needs
• True of all other essential nutrients

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Factors affecting Protein Requirements

• Physiological State
• Growth requires more than maintenance
• Prior nutrition state
• Depleted body reserves (muscle, organs) actually
  require less nitrogen to achieve balance
• More efficient absorption
• Decreased rate of catabolism

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Protein Requirements

• High quality diets 4-7 of ME as protein
• Low quality diets 20 of ME as protein
• Mixed protein sources 17-22 of ME as protein

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Protein Requirements

• 1974 vs. 1985 NRC
• 1974 much higher
• 1985 utilized highly purified AA sources for data
• Underestimated AA reqts.
• AAFCO (American Feed Control Officials) reverted
  back to 1974 reqt.
• Minimum 18 protein (DMB)
• 22 for growth and reproduction

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Lysine Requirement

• Increases as protein concentration increases
• First limiting in cereal based diets
• Susceptible to heat damage more so than other AA
• Decreases digestibility
• Meat proteins high in lysine

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Sulfur AA

• Methionine and Cysteine
• Met requirement met in part by dietary Cys
• ½ Met Reqt. met by Cys
• Reqt. is discussed as sum of 2 AA
• Differences noted among breeds of dogs
• Labradors Retrievers higher than Beagles
• Met is first limiting AA in meat/plant based pet
  foods

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The protein energy relationship

• Since energy needs of the dogs will be satisfied
  first, dietary energy concentration directly
  affects protein utilization/requirement
• Factors affecting energy expenditure and
  requirements must be considered when determining
  protein needs of the dog

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Energy

• Remember, all animals need to meet their energy
  needs
• Energy balance is achieved when calorie intake
  equals calorie expenditure
• Positive energy balance is achieved when calories
  ingtcalories out
• Extra calories used for
• Growing animals lean tissue
• Adult animals fat deposition

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Energy Expenditure

• Resting metabolic rate
• Voluntary muscular activity
• Meal-induced thermogenesis
• Adaptive thermogenesis

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Resting Metabolic Rate

• Accounts for greatest portion of animals total
  energy expenditure (60-75)
• Definition amount of energy cost of maintaining
  body functions in periods of rest
• Factor affecting gender, reproductive status,
  body composition, nutritional status

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Voluntary Muscular Activity

• Most variable component of energy expenditure
• Affected by duration and intensity of work and
  size and weight of the dog

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Meal-Induced Thermogenesis

• Refers to heat produced following consumption of
  a meal
• Result of metabolic cost of digestion,
  absorption, and metabolism
• Mixed diet 10 of calories used
• Affected by calorie and nutrient composition of
  the meal and nutritional status of the dog

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Adaptive Thermogenesis

• Additional energy expenditure
• Not conclusively established
• Changes in stresses
• Temperature, food intake, emotional stress

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Determination of Energy/Protein Requirements of
the Dog

• Total daily energy requirement is sum of energy
  that is needed for RMR, thermogenesis, and
  muscular activity
• Based upon metabolic body weight
• Amount of energy related to size and surface area
  of body

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Determination of MBW

• Takes the body weight of the dog in kilograms to
  the 0.67 power
• MBW BW (kg)0.67

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Determination of the Energy Requirements of Dogs

• ME requirement K BWkg0.67
• K 99 (inactive)
• K 132 (active)
• K 160 (very active)
• This formula is specific for adult maintenance

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Metabolizable Energy Requirements for Different
Stages of Life
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Suggested Minimum Level of Protein as of ME
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Protein Requirement in Various Physiological
States (NRC, 1985)
Assumes thermonuetral environment at moderate
levels of activity.