Regulation of Feed Intake and Energy Balance

1
Regulation of Feed Intake and Energy Balance
2
Regulation of Feed Intake and Energy Balance

• Long-term regulation of energy balance is
  achieved by short-term regulation of meal-eating
  and feed intake
• Energy balance, not feed intake, is the
  controlled variable in the homeostatic regulation
  of feed intake

3
Regulation of Feed Intake and Energy Balance
Energy balance
Gut, liver, CNS receptors
Feed intake () Energy expenditure (-)
Hypothalamic centers
4
Relation of Intake to Energy Balance

• In simple-stomached animals fed medium to high
  energy diets there is a simple negative relation
  between intake and diet energy content

5
Regulation of Feed Intake and Energy Balance
Energy
Intake
Dry matter
Energy concentration
6
Relation of Intake to Energy Balance

• In ruminants (and probably, other large
  herbivores) fed diets with a wider range of
  energy concentration, the relation is more
  complex (e.g. growing lambs).

7
Dry Matter Intake and Digestible Energy in Lambs

• Dry matter intake increases with dietary DE
  concentration to a maximum point (about 2.5
  Mcal/kg), then decreases with further increase in
  DE concentration.
• DE intake increases with dietary DE concentration
  to the same inflection point (about 2.5 Mcal/kg),
  then remains relatively constant.

8
Dry Matter Intake and Digestible Energy in Lambs

• Interpretation
• DE
• DE 2.5 Mcal/kg - intake is regulated by energy
  demand

9
Short Term Regulation of Feed Intake

• Intake is usually measured on a daily basis, but
  daily intake is comprised of a number of separate
  meals, even when animals are fed ad libitum (e.g.
  ruminants eat 10-15 "meals" per day. Should
  therefore focus on regulation of meal eating.

10
Effects on Feed Intake

• Two important factors are
• Meal interval
• Meal size

11
Regulation of Meal Eating

• Feedback signals
• Receptors
• CNS centers

12
Regulation of Feed Intake and Energy Balance
Energy balance
Gut, liver, CNS receptors
Feed intake () Energy expenditure (-)
Hypothalamic centers
13
Regulation of Meal Eating

• Feedback signals
• Changes in regulated variables which lead to meal
  eating being switched on or off
• Physical distension (gut fill)
• Chemical VFA concentration, pH, osmolarity of
  digesta
• Endocrine/neuroendocrine numerous hormones
  (insulin, leptin, ghrelin)

14
Regulation of Meal Eating

• Feedback signals
• Many signals operate at the same time
• Relative importance of different signals varies
  with diet (e.g., roughages vs concentrates),
  species (e.g., ruminant vs nonruminant) and
  physiological state (e.g., lactating vs
  nonlactating)

15
Regulation of Meal Eating

• Receptors
• Nerve ends which are sensitive to changes in
  feedback signals
• stretch receptors located in gut wall detect gut
  fill
• chemoreceptors located in various splanchnic
  tissues detect VFA (rumen wall), glucose (liver
  and other chemical changes

16
Regulation of Meal Eating

• CNS centers
• Where integration of afferent neural information
  from receptors takes place, and efferent signals
  to effector organs are initiated
• mainly in hypothalamus
• separate centers stimulate feeding (lateral
  hypothalamus) and satiety (ventromedial
  hypothalamus)

17
Long term Regulation of Feed Intake and Energy
Balance

• Involves modulation of level around which short
  term, homeostatic regulation occurs
• The major factor driving these chronic shifts in
  intake regulation is energy demand
• e.g., rat before, during and after lactation

18
Feed Intake in Rat

• Over 400 increase in feed intake during
  lactation
• Dramatic reduction after cessation of lactation

19
Long term Regulation of Feed Intake and Energy
Balance

• Another influence is climate, which also affect
  appetite via its impact on energy status
• Chronic shifts in energy demand can override not
  only metabolic but also physical feedback signals
  
• e.g., effect of lactation on maximum forage
  intake of pasture-fed dairy cows

20
Long term Regulation of Feed Intake and Energy
Balance

• Lactating cow increases her intake after calving
• Non-lactating maintained fairly constant intake
  until much later after calving