Flashcards in Voluntary Feed Intake Deck (23)
Give 3 ways to measure voluntary feed intake
Wet weight, dry matter, per unit of metabolic weight
- volume doesn't not = energy
What are the 10 theories of mechanisms of voluntary feed intake?
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
How may distension or fill feedback affect VFI?
- 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
Which VFAs decerase VFI? What else are they capable of?
Propionate to slightly less extent
Butyrate absorbed slowly, causes rumen stasis
Which other body factors can decrease VFI?
Body fat, preganancy
How does water in the rumen affect VFI?
> 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
How does DMI and transit time affect VFI?
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
How does inert fill affect VFI?
- 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
How does rumen outflow rate affect VFI?
- 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
How does post digestive feedback affect VFI?
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
Outline the HOT. Which species is this particularly applicable to?
Hepatic Oxidation Theory (Horse)
- ATP levels in liver determine vagal stim of hunger centre (negative feedback)
- sources of ATP in liver = VFAs, BHBA, NEFA
Outline the thermostatic theory
Animals eat to maintain body temp or more accurately to avoid hypothermia
Outline the lipostatic theory. How does this apply to dairy cows?
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
Which animals are kept on maintainence diets?
Pets doing NO EXCERCISE! Or weight loss
All other animals need maintainence + production
How can the DMI for a lactating dairy cow be calculated? Other animals?
> 2.5% BW + 10% milk yield (kg)
> Other animals 2% BW
> poultry higher (~7.5%)
What are the 2 sources of energy in forage?
- Cell contents (sugar,s tarch, protein) Digestable, rapidly available
- Cell walls (cellulose, lignin) More slowly availabl via fier-digesting bacteria
What are NDF and ADF?
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.
How do pregnancy energy requirements compare to lactation?
40mJ at term cf. milk 5MJ/L (cow lactates 30l/day -> 150MJ!
How much energy is 1kg body weight loss equivalent to?
What substances can reduce fermentation, DMI and general utilisation of food? (Anti-nutritional factors)
- 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
What does pica usually indicate?
Mainly an outdoor problem, indoor calves may develop
> herd level indicates
- mineral deficiency
- parasites or obesity
- under nutrition or low roughage feeds (lush grass)
- CNS problems
- metabolic disease (nervous ketoisis, hypomag etc.)
What may slurry or urine eating spread?