Voluntary Feed Intake

Question 1

Give 3 ways to measure voluntary feed intake

Answer 1

Wet weight, dry matter, per unit of metabolic weight

- volume doesn’t not = energy

Question 2

What are the 10 theories of mechanisms of voluntary feed intake?

Answer 2

1. Distension/fill feedback
2. VFAs, bosy fat, pregnancy etc
3. water in rumen
4. DMI transit time
5. Inert fill
6. Rumen outflow rate
7. Post-digestive feedback (glucostatic theory)
8. Hepatic oxidation theory (HOT)
9. Thermostatic theory
10. Lipostatic theory

Question 3

How may distension or fill feedback affect VFI?

Answer 3

• rumen adapts to loading (feed bulky food -> rumen stretch -> ^ feed intake)
• unlikely to be only factor as will eat in meals (in groups) rather than as rumen empties

Question 4

Which VFAs decerase VFI? What else are they capable of?

Answer 4

Acetate
Propionate to slightly less extent
Butyrate absorbed slowly, causes rumen stasis

Question 5

Which other body factors can decrease VFI?

Answer 5

Body fat, preganancy

Question 6

How does water in the rumen affect VFI?

Answer 6

> Water drunk with food, little effect
Water in food v VFI
^ water holding capacity = non-starch polysaccharides (soluble fibre) decreases VFI
physical fibre chopped ^ passage rate -> ^ VFI

Question 7

How does DMI and transit time affect VFI?

Answer 7

Different nutrients rretained for different lengths of time so nutritional value of food dependant on rate of feeding
- feed tables for nutritent content based on feeds at maintainence level

Question 8

How does inert fill affect VFI?

Answer 8

• decreases intake and ^ flow rate but NOT enough to compensate for lower intake
• similar effect as a growing foaetus
• ^ flow rate v fermentation so more digestable feed should be used

Question 9

How does rumen outflow rate affect VFI?

Answer 9

• main factor = particle size reaching omasum (due to ease of feed breakdown by chewing and fermentation)
• pressure in rumen may have some effect pushing feed out
• ruminal acidosis affects outflow -> loose dung and ^ particle size in dung

Question 10

How does post digestive feedback affect VFI?

Answer 10

Glucostatic theory - short term control (pigs, not poultry or cows)

• glucose Rs in CNS senstitve to rate of glucose use
• arterio-venous glucose differences indicate rate of glucose usage
• RUMINANTS gluconeogenesis from aas and propionic acid (no intake)
• normal plasma glucose 1/2 of non-ruminants
• CNS unusually INSENSITIVE to glucose changes

Question 11

Outline the HOT. Which species is this particularly applicable to?

Answer 11

Hepatic Oxidation Theory (Horse)

• ATP levels in liver determine vagal stim of hunger centre (negative feedback)
• sources of ATP in liver = VFAs, BHBA, NEFA

Question 12

Outline the thermostatic theory

Answer 12

Animals eat to maintain body temp or more accurately to avoid hypothermia

Question 13

Outline the lipostatic theory. How does this apply to dairy cows?

Answer 13

Leptin produced by fat tissue has negative effect on VFI
- role of leptin in domestic animals selected for increased growth and energy conversion UNKNOWN
> dairy cattle permenant negative energy balance -> sustained v plasma leptin
> despite NEB cows metabolism devoted to support of mammary metabolism
> reduction of plasma leptin may benefit early lactating dairy cows by promoting faster ^ feed intake

Question 14

Which animals are kept on maintainence diets?

Answer 14

Pets doing NO EXCERCISE! Or weight loss

All other animals need maintainence + production

Question 15

How can the DMI for a lactating dairy cow be calculated? Other animals?

Answer 15

> 2.5% BW + 10% milk yield (kg)
Other animals 2% BW
poultry higher (~7.5%)

Question 16

What are the 2 sources of energy in forage?

Answer 16

• Cell contents (sugar,s tarch, protein) Digestable, rapidly available
• Cell walls (cellulose, lignin) More slowly availabl via fier-digesting bacteria

Question 17

What are NDF and ADF?

Answer 17

ADF [acid detergent fibre] = Cellulose and Lignin (related to fiber digestability) remaining after boiling a sample in acid. Predicts energy content of forage (inverse related to digestability)
NDF [netural detergent fibre] = cell walls (hemicellulose, cellulose, lignin) related to DMI. Measure of fibre most useful I ni balancing rumen-healthy rations and predicting how much forage a cow can consume. Best measure of forage quality.

Question 18

How do pregnancy energy requirements compare to lactation?

Answer 18

Small!

40mJ at term cf. milk 5MJ/L (cow lactates 30l/day -> 150MJ!

Question 19

How much energy is 1kg body weight loss equivalent to?

Answer 19

25MJ

Question 20

What substances can reduce fermentation, DMI and general utilisation of food? (Anti-nutritional factors)

Answer 20

• Tannins - precipitate enzymes secreted by microbes
  Also v unpalatable so may v intake
• Oak poisoning -> GI ulceration => FATAL
• Legumes [beans, peas] cereals, potatoes - Protease inhibitors -> impaired growth and utilisation, ^ transit times v VFI
• Legumes also contain Lectins -> poor food utilization
• Oilseed rape and cabbage contain glucosinolates -> impair thyroid function
  > Usually only cause problems if >50% of diet

Question 21

What does pica usually indicate?

Answer 21

Mainly an outdoor problem, indoor calves may develop
> herd level indicates
- mineral deficiency
- parasites or obesity
- under nutrition or low roughage feeds (lush grass)
> individual
- CNS problems
- toxicity
- metabolic disease (nervous ketoisis, hypomag etc.)

Question 22

What may slurry or urine eating spread?

Answer 22

TB
Salmonella
Leptospira
BVD

Question 23

Why may slurry/urine eating occour?

Answer 23

Usually cows wintered indoors
- Low roughage diet 
- High milk yield
- Subclinical ketosis or acidosis 
- Mineral deficiency 
- Boredom? Learned vice? 
> No economic or health impact really