Voluntary Feed Intake

Question 1

Why is measuring voluntary feed intake of production animals important?

Answer 1

• Production (maximise intake)
• Economics (optimise intake)
• Weight control (balance intake and expenditure)
• Weight loss (reduce/minimise intake)

Question 2

What is distension or fill feedback in ruminants?

Answer 2

The more the rumen becomes distended/filled, the more the feed intake reduces

• Rumen wall stretch
• Message sent to brain to stop eating and start ruminanting

Question 3

What suggests distension/fill feedback in ruminants is not the only factor in determining voluntary feed intake?

Answer 3

If it was the only factor the cow would eat as and when the rumen empties bu they do tent to eat in phases

Question 4

What are the volatile fatty acids produced in ruminants? How do they impact on VFI?

Answer 4

\+ Acetate
% depression = (0.39 x acetate) - 5.18
More acetate = less intake
\+ Propionate
Almost as effective as acetate in causing depression
\+ Butyrate
Absorbed much slower from rumen, so more effective in causing ruminal stasis
Problem with poorly fermented feeds

Question 5

What factors decrease voluntary feed intake in ruminants?

Answer 5

Body fat
Pregnancy
Inert fill
Diet Neutral Detergent Fiber
Age
Growth rate
Production level
Environment
Stress
Food palatability

Question 6

When does water affect VFI?

Answer 6

Water drunk with food has little effect on VFI but water in plant material can have a significant effect on reducing VFI

Question 7

What is the water holding capacity of feed?

Answer 7

May be loosely regarded as soluble fibre or non-starch polysaccharides

Question 8

What is the effect of NSP (non-starch polysaccharides) on the GI of ruminants?

Answer 8

Slowing down the passage of feed through the intestines - this is good as allows for more absorption but must be balance to maximise intake

Question 9

What is inert fill?

Answer 9

Effect of bulky volume in cows abdomen either with rumen or outside the GI (e.g. foetus)

Question 10

How does inert fill affect rumen outflow rate?

Answer 10

Particle size reaching the omasum (<1 cm able to pass).

Depends on ease of feed breakdown by chewing/fermentation and pressure within rumen

Question 11

What disturbs rumen outflow rate?

Answer 11

Ruminal acidosis

Question 12

What is the glucostatic theory?

Answer 12

Short term control.
Glucoreceptors in CNS sensitive to rate of glucose use.
Low glucose use - excite neural activity to stimulate hunger sensations and vice versa for high.

Question 13

What is the hepatic oxidation theory?

Answer 13

ATP levels in liver determine vagal stimulation; low levels stimulate hunger centre

Question 14

What are sources for ATP in the liver in ruminants?

Answer 14

VFA
BHBA (Beta-hydroxy-butyric-acid)
NEFA (Non-esterified fatty acids)

Question 15

How does leptin affect VFI?

Answer 15

Decreased feed intake but in domestic animals selected for increased growth and energy conservation, role of leptin is largely unknown.

Question 16

How does severe negative energy balance influence VFI in dairy cows?

Answer 16

Cow’s metabolism is devoted to support of mammary metabolism (even in -ve energy balance)
Energy deficit = sustained reduction in plasma Leptin
Promotes faster increase in feed intake
Diverts energy from non-vital functions eg. reproduction

Question 17

How do we determine whether an animal is eating enough for:

a. Dairy cow
b. Beef cow

Answer 17

a. Milk production levels

b. Growth rate

Question 18

How is the required dry matter intake (DMI) estimated for a dairy cow?

Answer 18

2% BW (KG) + 10% milk yield (KG)

Question 19

What are the two sources of energy in forage?

Answer 19

1. Cell contents
   - Sugars, starches, proteins etc
   - 90% digestible and rapidly available
2. Cell walls
   - Cellulose, lignin, hemicellulose etc
   - 40-70% digestible, more slowly available by fibre digesting bacteria

Question 20

What does a high lignin content mean?

Answer 20

Pooper digestibility

Question 21

What is neutral detergent fiber (NDF)?

Answer 21

Measure structural components of plant matter (cell walls) e.g. lignin
NDF is best measure of forage quality and predicting how much forage a cow can consume

Question 22

What does a high NDF content lead to?

Answer 22

Decreased intake

Question 23

What is acid detergent fiber/

Answer 23

Chemical analysis that determines amount of residue eg. cellulose, lignin remaining after boiling feed sample in acid detergent.

Used to predict energy content of forages as it is inversely related to digestibility.

Question 24

Energy rquired for 650kg Holstein:

1. Maintenance
2. Milk production per litre
3. Pregnancy

Answer 24

1. 65MJ
2. 5MJ/L
3. 40MJ at term

Question 25

Is a cow designed to lose weight?

Answer 25

YES - Designed to lose about 1KG per day as energy is tranformed from body tissues

Question 26

What is the problems associated with tannins?

Answer 26

Tannins eaten in large quantity = reduce fermentation in rumen, reducing DMI.
Tannins also make food very unpalatable
Cause GI ulcerations

Question 27

What are the problems associated with lectins?

Answer 27

Lead to poor food utilization and impaired growth

Found in legumes, beans, lentils, peas

Question 28

What are the problems associated with glucosinolates?

Answer 28

Effect thyroid function

Found in cabbage and oil seed rape

Question 29

Give 2

Social factors
Ration factors
Cow factors
that affect VFI

Answer 29

Feed space, stocking density
TMR, chopping length
Palatability, adaption time