Voluntary Feed Intake Flashcards
What is the best measure of voluntary feed intake?
Dry matter intake
Why is voluntary feed intake important?
Production - want to maximise intake
Economics - want to optimise intake
Weight control - balance intake and expenditure
Weight loss- reduce intake
Which cows should NOT be losing weight?
Dry cows
What factors can decrease VFI?
Body fat
Pregnancy
Inert fill (similar to distension feedback)
Diet NDF
What does NDF stand for?
Neutral Detergent Fibre
How does distension feedback affect feeding of dry cows?
Feed dry cows to their abdominal fill needs
- Will continue to eat SAME VOLUME when lactating
Change quality/content to suit needs but keep volume the same
When does water affect VFI?
Water drunk WITH dry food - LITTLE EFFECT
Water IN plant material has significant effect
Why does water in plant material affect VFI?
Plants have to be broken down before water can be released - BULK is still there
What are NSPs and how can they affect feeding ?
Non- Starch polysaccharides / SOLUBLE FIBRE
Slows down the passage of feed and attracts fluids.
Better absorption of nutrients BUT reduced feed intake
What is the effect of giving chopped fibre?
Quicker transit
Increased feed intake
How is DMI related to transit time?
Increased dry matter intake results in shorter time spent in rumen/gut.
This affects how well nutrients are digested
What are feed tables for nutrient content based on?
How could this issue be overcome?
Maintenance level feed
NEVER occurs in dairy cows
Correction factors in modern software
What is inert fill?
How does it affect feeding?
Something in the abdomen (e.g. twins in cow or triplets in sheep) pushing on GIT
Intake drop, flow rate increases - POOR INTAKE
How can you counteract the effects of inert fill?
Feed more digestible feed to affected cows
What is the major factor affecting rumen outflow rate?
Particle size reaching the omasum
Pressure within rumen may have SOME effect in pushing feeds through
What affects particle size reaching the omasum (therefore rumen outflow rate)?
Ease of feed breakdown by chewing and fermentation
What effect can ruminal acidosis have on rumen outflow?
How might this be reflected in faeces?
More pressure in rumen due to stasis
May push through feeds without being fully digested
See indigested feed in dung
How can VFAs affect the rumen?
Feed back negatively on feed intake
Acetate and Proprionate almost same effect (Acetate slightly more effective)
Butyrate absorber slowe (as bigger) and more effective in causing ruminal stasis
What is heat stress in cows?
How does it affect feeding?
When it gets warmer, cows start eating less (above around 34 degrees)
Outline the glucostatic theory of post digestive feedback.
What is the impact of this theory on ruminants?
If you have either a low glucose level in blood or a high glucose utilisation rate, it will trigger the hunger centre in the hypothalamus and therefore increase feed intake
LIMITED - short term control of appetite
What are the main sources of glucose in ruminants?
Hepatic gluconeogenesis from amino acids and proprionic acid
Why is the glucostatic theory of post digestive feedback of limited importance in ruminants?
Ruminant CNS is unusually INSENSITIVE to changes in blood glucose
What is the Hepatic Oxidation Theory (HOT)
ATP levels in the liver determine the vagal stimulation
Low levels = stimulated hunger centre
What are the sources of ATP in the liver?
VFA
Beta hydroxy butyrate - KETOSIS
NEFA - FATTY LIVER
These therefore feed back negatively on VFI
What is leptin produced by?
What determines the level of leptin in the circulation?
fat tissue
More fat = more leptin in circulation
UNKNOWN role in domestic animals
What is the role of leptin?
Inhibits hunger
How could leptin be beneficial to dairy cows?
Energy deficit causes sustained reduction in leptin
Could benefit early lactating cows by promoting faster increase in feed intake and diverting energy from non-vital functions
What factors affect how much an animal can eat?
Weight Age Growth rate Production level Health Environment Non-production activity e.g. walking Stress Food palatability Food type Water Food availability
How can we estimate the DMI of a dairy cow?
How might this vary for smaller animals?
2.5% body weigh (kg) + 10% milk yield (Kg)
Smaller animals, higher index
What animals would be fed to be kept at maintenance balance?
Companion animals
What is the energy requirement of milk production per litre?
5MJ/L
What is the result of giving a ration that is too high in energy?
Rumen acidosis
Why might weight loss during milking be beneficial?
CONTROLLED temporary negative energy
Decreased energy requirement for feed
Healthier rumen
What are the sources of energy in forage?
How does their availability vary?
Cell contents - sugars, starches, proteins - 90% digestible, READILY AVAILABLE
Cell walls - cellulose, lignin, hemicellulose
SLOWLY AVAILABLE by fibre digesting bacteria
— good for bulk not energy requirement
How does the percentage of lignin in a plant vary with age?
How does this effect digestibility?
INCREASES
Decreases as lignin is indigestible
What does NDF stand for?
Non detergent fibre
What are the constituents of NDF?
CELL WALLS
Hemicellulose,
Cellulose
Lignin
How does %NDF affect feed intake ?
Measure of forage quality
Decreased NDF = increased intake
What is acid detergent fibre?
What is it used to predict?
Cellulose and lignin
energy content of forage
Inversely related to digest ability
What is the relationship between silage pH and intake?
How could this be explained?
Slight positive relationship at low pH
Adverse effect of acidity on fermentation need to eat more
What are antinutritional factors?
Tannins
Lectins
Glucosinolates
Saponins
What effect do tannins have at low and high quantities?
Low - destroyed in rumen
High - caustic to gut lining resulting in gut ulceration (oak poisoning)
What are lectins?
How do they affect feeding ?
Glycoproteins found in legumes
Poor food utilisation and impaired growth
What are glucosinolates?
How can they affect feeding?
found in cabbage and oil seed rape
Effects thyroid function
What are saponins?
How can they affect feeding?
Found in soybeans peanuts sugar beets
Soapy - can affect rumen flora
What ‘other’ factors (social, ration, cow) can affect VFI?
Feed space
Stocking density
TMR
Chopping length
Palatability
Adaptation time
