REGULATION OF VOLUNTARY FEED INTAKE

Question 1

Reasons for intervention

Answer 1

1. RESTRICTION OF FEED INTAKE E.g. breeding animals, obese animals etc.;
2. INCREASE OF FEED INTAKE E.g. high lactating dairy cows, broiler chicks, sick animals etc.
   - Effect of body condition on feed intake: setting up the required body condition (e.g. dairy cows, pregnant sows etc.).

Question 2

PREDICTION OF THE FEED INTAKE

Answer 2

Significance - setting up the nutrient density of diets made for monogastric animals,
- setting up the nutrient density of daily rations made for ruminants

Question 3

Factors affecting feed intake. 1. Native status

Answer 3

• The role of feed energy („animals eat for calories)”:
  e.g. rabbits, laying hens, rodents: self regulation of feed intake according to the energy density of feeds  =>possibility of ad libitum feeding;
• other factors e.g. 
  Na, 
  ruminants: gastrointestinal capacity =>continuous and selective grazing,
• predators: overeating, social effects, energy investment.

Question 4

Factors affecting feed intake. 2. Effect of Domestication

Answer 4

E.g. swine: having been selected for body weight gain = selection for higher feed intake, =>they lost the ability of regulation according to the feed energy, 
hand feeding is required

Question 5

Types of regulation

Answer 5

I. QUALITATVE REGULATION (What to eat?) - taste (human, swine, rat); - smell, adaptation (cats); - physical form (birds); - imitation (sheep, poultries); - enviousness, jealousy (dogs, cats).
II. QUANTITATIVE REGULATION (How much to eat?)
II/1. Short term control
II/2. Long term control
Both of them are regulated by the a) central nervous system, and by the b) peripheral signals.

Question 6

II/1. Short term control (homeostatic control)

Answer 6

Role: - assurance of the homeostasis;
Central Nervous System (Hypothalamus):
- regulation of feed intake,
- regulation of reproduction (sexual steroids); Hypothalamic peptides:
- anabolic peptides => increase the feed intake (e.g. neuropeptide Y (NPY) – „central hunger peptide”),
- catabolic peptides =>decrease the feed intake (e.g. corticotrophin-releasing hormone /CRH/).

Peripheral signals

1. Positive feedbacks: increase the feed intake e.g. Stomach  GHRELIN („peripheral hunger peptide”);
2. Negative feedbacks: decrease the feed intake (gastrointestinal peptides) e.g. small intestine  Cholecystokinin (CCK).

Some other factors:
1)Physical factors (especially in ruminants):
capacity of the gastrointestinal tract, bulkiness, passage; 2)Chemical factors:
- blood glucose: in monogastric animals,
- blood volatile fatty acids (VFA): ruminants, rabbit,
- blood amino acid level: in all animal species,
- blood pH, osmotic pressure of blood (tap water),
- body temperature, temperature of the feed,
- higher feed intake =>increased heat production (ruminants – digestion work) etc.

Question 7

II/2. Long term control (homeorhetic control)

Answer 7

Role: - assurance of the normal body weight, E reserves, body composition for longer periods (e.g. pregnancy, lactation etc.); high body fat content ≠ obesity (pl. bear, seal, migrating birds etc.).
Central Nervous System (Hypothalamus):
like in the short term control - regulation of feed intake, - regulation of reproduction (sexual steroids); Hypothalamic peptides: like in the short term control
- anabolic peptides=>increase the feed intake (e.g. neuropeptide Y (NPY) – „central hunger peptide”),
- catabolic peptides => decrease the feed intake (e.g. corticotrophin-releasing hormone /CRH/).

Peripheral signals

1. Negative feedback (decreased feed intake) (Leptin: „leptos” = lean, thin) Over condition => increased adipocytes => more LEPTIN (hormone) produced=>  reduces the secretion of NPY(anabolic peptide of hypothalamus) => feed intake decreases;
2. Positive feedback (increased feed intake): the opposite of the previous process;

Prerequisites of this mechanism: presence of leptin receptors: hypothalamus, ovary, uterus etc.,
Practical importance: fatty cow syndrome!
LIPOSTATIC CONTROL of feed intake

Question 8

Genetic Background

Answer 8

1. OB/OB and OB/ob: enough leptin is produced; ob/ob: insufficient leptin production =>obesity;
2. Leptin receptor mutant mice (db/db)  insufficient amount of leptin receptors =>obesity;
3. Insufficient amount of CKK (decreases the feed intake) receptors =>obesity.