Regulation of feed intake. Nutrients’ Digestability

Question 1

Factors affecting feed intake

Answer 1

1. Native status
   - Some animals can self-regulate the feed intake (e.g. rabbits, poultries, rodents) according to the energy density of feeds -> possibility of ad libitum feeding
   - Gastrointestinal capacity (ruminants, horses) -> continuous and selective grazing
2. Domestication (e.g. pigs lost the ability of feed intake regulation according to the feed energy)

Question 2

Types of regulation of feed intake

Answer 2

1. Qualitative regulation (WHAT to eat)
2. Quantitative regulation (HOW MUCH to eat)

Question 3

Qualitative regulation of feed intake. Influencing factors

Answer 3

• taste (human, swine, rat)
• smell, addiction (cats)
• physical form of feed (birds)
• imitation (sheep, poultry)
• jealousy (goes, cats)

Question 4

Quantitative regulation of feed intake

Answer 4

1. Short-term control
2. Long-term control
   —
   Both of them are regulated by CNS and peripheral signals

Question 5

Short term control of quantitative regulation of feed intake

Answer 5

1. CNS: hypothalamus: via hypothalamic peptides:
   - anabolic peptides -> increase the feed intake;
   - catabolic peptides -> decrease there feed intake
2. peripheral signals:
   - positive feedbacks (e.g. grelin (“peripheral hunger peptide”);
   - negative feedbacks (e.g cholecystokinin (CCK)
   - **physical factors (especially in ruminants): capacity of GIT, bulkiness, passage ; body temperature
   - chemical factors: blood glucose, blood VFA, blood amino acid level, osmotic pressure of the blood (

Question 6

Possible genetic reasons of obesity

Answer 6

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

Question 7

Apparent digestibility vs true digestibility

Answer 7

Apparent digestibility:
(Intake N - output N) / intake N

Theoretical background: feces contain only the indigested (unabsorbed) part of feed
—
True digestibility: feces also contain some endogen N. It’s not originated from the indigestible protein, it comes from erosion of epithelial cells from the gut wall and rests of enzymes
CORRECTION:
(N intake - N output + endogen N)/N intake

Question 8

Determination of nutrients’ digestability

Answer 8

1. Faecal digestibility (difference between the feed and feces)
2. Ideal digestibility (difference between the feed and the digesta in small intestine)