Voluntary Feed Intake Flashcards

1
Q

Give 3 ways to measure voluntary feed intake

A

Wet weight, dry matter, per unit of metabolic weight

- volume doesn’t not = energy

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2
Q

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

A
  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
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3
Q

How may distension or fill feedback affect VFI?

A
  • 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
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4
Q

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

A

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

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5
Q

Which other body factors can decrease VFI?

A

Body fat, preganancy

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6
Q

How does water in the rumen affect VFI?

A

> 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

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7
Q

How does DMI and transit time affect VFI?

A

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

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8
Q

How does inert fill affect VFI?

A
  • 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
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9
Q

How does rumen outflow rate affect VFI?

A
  • 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
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10
Q

How does post digestive feedback affect VFI?

A

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
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11
Q

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

A

Hepatic Oxidation Theory (Horse)

  • ATP levels in liver determine vagal stim of hunger centre (negative feedback)
  • sources of ATP in liver = VFAs, BHBA, NEFA
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12
Q

Outline the thermostatic theory

A

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

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13
Q

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

A

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

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14
Q

Which animals are kept on maintainence diets?

A

Pets doing NO EXCERCISE! Or weight loss

All other animals need maintainence + production

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15
Q

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

A

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

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16
Q

What are the 2 sources of energy in forage?

A
  • Cell contents (sugar,s tarch, protein) Digestable, rapidly available
  • Cell walls (cellulose, lignin) More slowly availabl via fier-digesting bacteria
17
Q

What are NDF and ADF?

A

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.

18
Q

How do pregnancy energy requirements compare to lactation?

A

Small!

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

19
Q

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

A

25MJ

20
Q

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

A
  • 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
21
Q

What does pica usually indicate?

A

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.)

22
Q

What may slurry or urine eating spread?

A

TB
Salmonella
Leptospira
BVD

23
Q

Why may slurry/urine eating occour?

A
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