Voluntary Food Intake

What is it?
1. Factor limiting animal production
2. Needs to be predicted in ration formulation
3. Controlled by
  1. Physiological factors
    1. Important for ruminants
      1. Low Quality diets = stop eating at gut fill
        AS diet quality increases, intake goes up to an optimum point where nutritional requirements are satisfied, then DMI is reduced to maintain nutrient supply
  2. Physical factors
    1. Important for pigs & poultry
      1. Higher quality diet
  3. Psychological factors
Physiological Factors
1. Hunger
  1. Controlled by Hypothalmus
  2. Stimulation
    1. Thermostatic
      1. Animal monitors heat production - eats more when its cold to raise body temperature
    2. Lipostatic
      1. Brain monitors body composition and animals eat to maintain fat levels. Fat animals eat less. They want to achieve there genetically determined body composition
    3. Chemostatic (most likely
      1. Level of circulating nutrients drop so animals eat. Brain monitors circulating glucose. Also monitor VFA's, Minerals, AA, Vits, Hormones.
        Affected by physiological state
        Pregnant
        Lactating
        Age
Physical Factors
1. Gut Fill
  1. Depends on
    1. Gut/Rumen Size
      1. Animal breed or Size
      2. Pregnant? - Foetal mass constricts rumen size
      3. Body Composition - fat animals eat less than thin animals
    2. Rate of Passage
      1. Effected by chemical composition and physical form of diet
        Low RDP = Low microbial activity = Low DMI
        High starch = reduced pH = low microbial acivity = low DMI
        Particle size: chop and grind = particle size down = rate of passage up = DMI up
      2. Poor quality forage= slow digestion = low DMI
        Add NaOH / NH3 to increase digestibility.
      3. Good quality forage = quick digestion = high DMI
      4. Generally, D Value up = digestibility up (not linear)
Psychological factors
1. Appetite
  1. Smell, taste, site, sound, texture of diet.
  2. Diet perception effected by: feed, animal and environment
Prediction
1. Difficult!
2. Physiological, physical and psychological components work together

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Voluntary Food Intake

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	Created by Greg Parkes over 11 years ago