Voluntary Feed Intake Flashcards
Why is measuring voluntary feed intake of production animals important?
- Production (maximise intake)
- Economics (optimise intake)
- Weight control (balance intake and expenditure)
- Weight loss (reduce/minimise intake)
What is distension or fill feedback in ruminants?
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
What suggests distension/fill feedback in ruminants is not the only factor in determining voluntary feed intake?
If it was the only factor the cow would eat as and when the rumen empties bu they do tent to eat in phases
What are the volatile fatty acids produced in ruminants? How do they impact on VFI?
\+ 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
What factors decrease voluntary feed intake in ruminants?
Body fat Pregnancy Inert fill Diet Neutral Detergent Fiber Age Growth rate Production level Environment Stress Food palatability
When does water affect VFI?
Water drunk with food has little effect on VFI but water in plant material can have a significant effect on reducing VFI
What is the water holding capacity of feed?
May be loosely regarded as soluble fibre or non-starch polysaccharides
What is the effect of NSP (non-starch polysaccharides) on the GI of ruminants?
Slowing down the passage of feed through the intestines - this is good as allows for more absorption but must be balance to maximise intake
What is inert fill?
Effect of bulky volume in cows abdomen either with rumen or outside the GI (e.g. foetus)
How does inert fill affect rumen outflow rate?
Particle size reaching the omasum (<1 cm able to pass).
Depends on ease of feed breakdown by chewing/fermentation and pressure within rumen
What disturbs rumen outflow rate?
Ruminal acidosis
What is the glucostatic theory?
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.
What is the hepatic oxidation theory?
ATP levels in liver determine vagal stimulation; low levels stimulate hunger centre
What are sources for ATP in the liver in ruminants?
VFA
BHBA (Beta-hydroxy-butyric-acid)
NEFA (Non-esterified fatty acids)
How does leptin affect VFI?
Decreased feed intake but in domestic animals selected for increased growth and energy conservation, role of leptin is largely unknown.
How does severe negative energy balance influence VFI in dairy cows?
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
How do we determine whether an animal is eating enough for:
a. Dairy cow
b. Beef cow
a. Milk production levels
b. Growth rate
How is the required dry matter intake (DMI) estimated for a dairy cow?
2% BW (KG) + 10% milk yield (KG)
What are the two sources of energy in forage?
- Cell contents
- Sugars, starches, proteins etc
- 90% digestible and rapidly available - Cell walls
- Cellulose, lignin, hemicellulose etc
- 40-70% digestible, more slowly available by fibre digesting bacteria
What does a high lignin content mean?
Pooper digestibility
What is neutral detergent fiber (NDF)?
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
What does a high NDF content lead to?
Decreased intake
What is acid detergent fiber/
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.
Energy rquired for 650kg Holstein:
- Maintenance
- Milk production per litre
- Pregnancy
- 65MJ
- 5MJ/L
- 40MJ at term
Is a cow designed to lose weight?
YES - Designed to lose about 1KG per day as energy is tranformed from body tissues
What is the problems associated with tannins?
Tannins eaten in large quantity = reduce fermentation in rumen, reducing DMI.
Tannins also make food very unpalatable
Cause GI ulcerations
What are the problems associated with lectins?
Lead to poor food utilization and impaired growth
Found in legumes, beans, lentils, peas
What are the problems associated with glucosinolates?
Effect thyroid function
Found in cabbage and oil seed rape
Give 2
Social factors
Ration factors
Cow factors
that affect VFI
Feed space, stocking density
TMR, chopping length
Palatability, adaption time
