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The estimation of digestibility Faecal collection on pasture.

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Presentation on theme: "The estimation of digestibility Faecal collection on pasture."— Presentation transcript:

1 The estimation of digestibility Faecal collection on pasture

2 Advanced Feed Science 2013 Rumen metabolism

3 Metabolic crate for sheep

4 Feed intake(I) = disappearance(X) + faecal output 1 = X X = 0.8 Digestibility = X / I = 0.8 / 1 = 0.8 Apparent digestibility of the total feed FeedFaeces X Note: total feed and faeces are weighed for a given period!

5 Feed intake(I) = disappearance(X) + faecal output 0.4*1 = X + 0.3*0.2 X = = 0.34 Digestibility = X / I = 0.34 / 0.4 = 0.85 Apparent digestibility of a feed component Faeces 0.2 Feed X

6 Digestibility of a feed ingredient by difference Diet 1: Basal feed Diet 2- : Basal feed + test feed at one or more levels Calculations by difference or by regression Problems: interactions between feeds

7 The effects of positive and negative feed interactions

8 True and apparent digestibility True digestibility is always higher than apparent if any metabolic or endogenous components are excreted in the faeces Metabolic components consist of: crude protein, lipids, soluble carbohydrates and soluble ash Metabolic components are coming from the microbes and are soluble in neutral detergents App. dig. = true dig. - metabolic fraction Is true fiber digestibility higher than apparent?

9 Factors affecting digestibility Feed quality Feed interactions (examples) starch: fibre digestibility in ruminants protein: fibre digestibility in ruminants lipids: Ca and Mg utilisation Level of intake - effect on fibre utilisation Physical form - effect on fibre utilisation Fats: chain length, degree of saturation Processing: proteins, starch, etc. Adaptation of gut microflora Animal age: e.g. starch, lipids, fibre

10 Use of markers - case studies 1. Digestibility - total digestive tract 2. Flow - ruminal 3. Intake 4. Methane emission 5. Microbial amino acid absorption

11 Use of markers to estimate digestibility, intake and flows Markers must not be absorbed or interfere with the digesta or adhere to tissues, etc. External markers: known amounts of dosed markers Internal markers: components of the feed or produced in metabolism.

12 Digestibility is calculated as: ( /0.03)*100 = 67% Note: The marker is given regularly and is not absorbed. 1. Digestibility: measured by a dosed marker or by a marker with known concentration in the feed FeedFaeces Marker: 3% 100 Marker: 1% 100

13 Faecal flow is calculated as: 2/1 = 2.0 kg/d Note: The marker is given regularly and is not absorbed. 2a. Intake during grazing: faecal output is first measured by a continuously dosed marker FeedFaeces Marker: 1 g/kg Marker: 2 g/d

14 2b. Intake during grazing: intake is then estimated We now know flow of undigested feed (2a) We must determine digestibility separately Flow of indigestible feed = 2 kg/d Digestibility determined (hand clipped grass in vitro or in vivo) = 70% Intake of grass = 2/(1 – 0.70) = 6.7 kg/d

15 3 a. Methane emission Gas sampling device

16 3 b. Methane emission SF 6 delivery device SF 6 permeable membrane

17 3 c. Methane emission SF 6 delivery = 3 mg/d SF 6 concentration in collected air = 0.01 mg/g methane Methane produced = 3/0.01 = 300 g/d

18 4. Estimating microbial amino acid flow from the rumen

19 Rumen & reticulum Omasum Abomasum Easophagus

20 Protein metabolism Liver Rumen Feed and microbial protein Small intestine AmmoniaAmino acids Urine Feed protein Other organs Amino acids Urea

21 Digestive tract metabolism of nucleic acids Rumen Feed nucleic acids Nucleic acids Metabolized Nucleic acids (RNA) Bacterial synthesis Hydrolysis Acid stomach Small intestine Nucleosides & bases To liver

22 Liver metabolism of the purine bases NH 3 AMP & GMP XanthineHypoxanthine Uric acidAllantoin Inosine Urine IMP Guanine Guanosine NH 3

23 Muscle turnover Muscles Creatine-P + ADP ATP + Creatine Liver Amino acids + Creatinine +Creatine Muscle turnover Urine Creatinine, Creatine, (amino acids) Other organs Amino acids

24 Concentrations in urine and usefulness Compoundg/LNotesUsage Urea~20Excretion depends on diet balanceN efficiency Creatine~1 Creatinine~1Constant muscle turnoverUrine volume Allantoin~1.8Depends on microbial growthMicrobial synthesis Hippuric acid~5 Amino acids~0.8

25 Estimation of microbial amino acid uptake 1. You assume a constant creatinine excretion per day (g/d) 2. You calculate urine excretion (L/d) from #1 divided by creatinine concentration in urine (g/L) 3. You calculate allantoin excretion (g/d) from #2 times allantoin concentration in urine (g/L) 4. You finally calculate microbial amino acid absorption (g/d) assuming a relationship between microbial amino acid absorption and allantoin excretion in urine. The basis for that is an assumed RNA/amino acid ratio in rumen bacteria

26 Demonstrations and visit to Kungsängen research facilities Rumen fistulation – film (optional) Digestibility - sheep and cattle crates Equipment for monitoring methane emission Macro in vitro system (“Rörko”) Milk analysis Mini-silos Aerobic stability of silage

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