Nutritional Indices

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Nutritional Indices

• Determining the nutritional quality of the
  environment can be difficult by quantifying foods
  available and their quality
• Alternative is to measure the nutritional
  condition of the animals themselves
• Indices generally based on measuring energy
  status, but measures of forage quality and
  productivity also used
• Extracting fat from animals best, but time
  consuming and requires death of animal

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Nutritional Indices

• Fecal indices
• Fecal Nitrogen
• Generally related positively to dietary N dry
  matter digestibility (Osborn and Ginnett WSB
  241135)
• Tannins can inflate fecal N
• What species would fecal N work for and which
  would you want to be cautious?
• Rumen contents nitrogen
• Related positively to dietary N dry matter
  digestibility. Tannins may cause problems

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Nutritional Indices

• DAPA (2, 6 diaminopinelic acid)
• Amino acid found in bacterial cell walls
• Most fecal N is from endogenous sources,
  primarily bacterial
• Concentration related to digestibility of diet
• May also be related to dietary protein. Why?
• Not as susceptible to problems with dietary
  tannin

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Nutritional Indices

• Animal condition or nutritional status
• Antler size in cervids
• Antler size influenced by nutrient intake
  (protein, energy, minerals) age and genetics
• Often use yearling antler characters. Why?
• Body mass
• Better fed animals grow larger
• Often use body mass of yearling animals
• How to account for body frame size?

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Nutritional Indices

• Ratio measures
• Correct for body frame size by dividing body mass
  by measure of body size
• Body mass divided by wing length, leg length,
  body length, etc
• Body fat measures
• Fat represents stored (excess) energy
• Gold standard is to grind animal and extract fat
  (ether extract)
• Difficult, so use indirect measures of body fat

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Nutritional Indices

• Marrow fat
• Marrow is firm and white if lots of fat, soft and
  pinkish if not a lot of fat, and gelatinous red
  if no fat. If red, animal starving.
• Objective measure using ether extract of marrow
• Can be collected even if carcass scavenged

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Nutritional Indices

• Marrow fat
• Marrow is firm and white if lots of fat, soft and
  pinkish if not a lot of fat, and gelatinous red
  if no fat. If red, animal starving.
• Objective measure using ether extract of marrow
• Can be collected even if carcass scavenged
• Kidney fat
• Remove kidney and adhering fat. Trim fat from
  ends of kidneys, then weigh remaining fat and
  kidney. Index fat/kidney100

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Nutritional Indices

• Subcutaneous fat
• Recent work in cervids shows good relationship
  between total body fat and subcutaneous fat
• Can measure subcutaneous fat via ultrasound
• Technique is tricky and requires training
• Loses resolution at very low (lt5) amounts of
  body fat
• Ultrasound has also been used to estimate size of
  fat deposits in birds
• In some birds can see fat through skin

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Nutritional Indices

• If we can measure water in an animals body, we
  can predict the amount of fat
• Use isotope dilution to estimate water in body

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Nutritional Indices

• Other techniques to estimate body composition
• Electrical impedance
• Hook wire to animals lips and posterior end
• Measure electrical impedance
• Greater impedance means less water and more fat
• DXA - Dual-energy X-ray absorptiometry
• Fat, lean mass, and body attenuate photons from
  x-ray differently. Computer can use information
  from photon attenuation to determine body
  composition.
• EmScan - place animal in an electrical coil
• Machine estimates bodies conductivity, which is
  related to fat content

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Nutritional Indices

• Serum Chemistry
• Many chemicals of nutritional importance
  transported in blood
• Often concentrations do not change as much as
  turnover rates (e.g. glucose or FFA)
• Recognize concentrations have daily and seasonal
  patterns that could cause bias or low resolution
• Need to standardize sampling

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Nutritional Indices

• Urea nitrogen
• Urea used to excrete excess nitrogen
• High urea N means animal is eating excess protein
  or is using muscle as an energy source
• Must differentiate between consumption of high
  quality diet and starvation
• Can be measured in serum or in urine
• In northern states collect urine in snow

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Nutritional Indices

• Triiodothyronine (T3) and Thyroxine (T4)
• Hormones that regulate cellular metabolism
• T3 appears to be related to energy status in
  deer. No consistent relationships in other
  species
• Erin Monaco has evidence that T4 is related to
  energy status in white-tailed deer

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Nutritional Indices