‘IN VITRO GAS PRODUCTION TECHNIQUE’FOR EVALUATION OF RUMINANT FEED STUFFS

Dr. Avijit Dey, M.V.Sc., Ph.DDr. Avijit Dey, M.V.Sc., Ph.D

NEED OF IN VITRO STUDIES…

Nutritive value or energy content of an animalfeed- Intake & Digestibility- Productiveperformance

In vivo and in situ methods are i) laborious &expensive ii) large quantity of feed required iii)unsuitable for large scale of feed evaluation

In vitro technique- Rapid and routine evaluation ofnutritive value of large no of samples

Nutritive value or energy content of an animalfeed- Intake & Digestibility- Productiveperformance

In vivo and in situ methods are i) laborious &expensive ii) large quantity of feed required iii)unsuitable for large scale of feed evaluation

In vitro technique- Rapid and routine evaluation ofnutritive value of large no of samples

TILLEY- TERRY METHOD VS GAS PRODUCTION

End point measurement- gives only oneobservation, lengthy and time course studiesrequired

Overestimates DMD

Does not provide information on kinetics offorage digestion

End point measurement- gives only oneobservation, lengthy and time course studiesrequired

Overestimates DMD

Does not provide information on kinetics offorage digestion

IN VITRO GAS METHOD(MENKE ET AL., 1979; STEINGASSAND MENKE, 1986; BLUMMEL ET AL., 1997)

Rumen fluid collection& preparation under CO2

Syringe (100 ml)& Buffered Mineral solpreparation

at 390c

Filling of syringe(30 ml)

under Co2

Addition of rumen fluidinto the medium (1:2)

Weigh feed sample(200mg)

Filling of syringe(30 ml)

under Co2

Initial readingIncubate the syringe

for 24 h at 39oC

Addition of rumen fluidinto the medium (1:2)

Final reading

Degradability, CH4,NH3, VFA

ORIGIN OF GAS

Products of microbial degradation- SCFA+MBP+ Fermentive gas (mainly CO2 & CH4)

Gas produced as a result of fermentation ofCHO to SCFA (acetate, propionate andbutyrate)

From protein- small, fat- negligible

Gas prod ∞ acid prod- indicator of extent andrate of feed digestion

Products of microbial degradation- SCFA+MBP+ Fermentive gas (mainly CO2 & CH4)

Gas produced as a result of fermentation ofCHO to SCFA (acetate, propionate andbutyrate)

From protein- small, fat- negligible

Gas prod ∞ acid prod- indicator of extent andrate of feed digestion

APPLICATION OF IN VITRO GAS METHOD

GAS PRODUCTION AND SUBSTRATE DEGRADABILITY

True substrate degradability is determined bytreatment of incubation residues with NDS(Goering and van Soest, 1970; Blummel et al., 1997)

TDDM = Feed (DM) incubated - residue (DM)

TDOM = Feed (OM) incubated - residue (OM)

OMD% =14.88+0.889 x net Gp (24 h) +0.45 x

CP (%DM)+ 0.0651XA (% DM)

True substrate degradability is determined bytreatment of incubation residues with NDS(Goering and van Soest, 1970; Blummel et al., 1997)

TDDM = Feed (DM) incubated - residue (DM)

TDOM = Feed (OM) incubated - residue (OM)

OMD% =14.88+0.889 x net Gp (24 h) +0.45 x

CP (%DM)+ 0.0651XA (% DM)

PREDICTION OF METABOLIZABLE ENERGY

ME content of a feed can be predicted more

accurately from gas volume and chemical

composition rather than chemical composition only

ME (MJ / Kg DM) for forages = 2.20 + 0.136 Gp +

0.057 CP+0.0029EE

ME (MJ / Kg DM) for grains and by products=

1.06+ 0.157 Gp + 0.0084CP+ 0.022 EE-0.0081CA

ME content of a feed can be predicted more

accurately from gas volume and chemical

composition rather than chemical composition only

ME (MJ / Kg DM) for forages = 2.20 + 0.136 Gp +

0.057 CP+0.0029EE

ME (MJ / Kg DM) for grains and by products=

1.06+ 0.157 Gp + 0.0084CP+ 0.022 EE-0.0081CA

PREDICTION OF SCFA PRODUCTION

The SCFA production could be predicted fromgas values using the relationship

SCFA = 0.0239Gp -0.0601; R2 = 0.953 The level of SCFA-indicator of energy

availability to the animal Prediction of SCFA from in vitro gas

measurement will be increasingly importantin developing countries where laboratories areseldom equipped with modern equipments tomeasure SCFA.

The SCFA production could be predicted fromgas values using the relationship

SCFA = 0.0239Gp -0.0601; R2 = 0.953 The level of SCFA-indicator of energy

availability to the animal Prediction of SCFA from in vitro gas

measurement will be increasingly importantin developing countries where laboratories areseldom equipped with modern equipments tomeasure SCFA.

MICROBIAL BIOMASS PRODUCTION ANDVOLUNTARY FEED INTAKE

In vitro gas measurement reflects only SCFAproduction

Inverse relationship between gas production andMBP

Microbial mass (mg) = mg substrate trulydegraded - (ml gas volume x 2.2)

PF= mg substrate truly degraded /vol of gas ml ↑PF- ↑DMI, ↓CH4 Forages with high voluntary DMI have high gas

volumes at early incubation times (i.e., 2-8 h) andhigh substrate true degradabilities but low gasproduction at later times of incubation

In vitro gas measurement reflects only SCFAproduction

Inverse relationship between gas production andMBP

Microbial mass (mg) = mg substrate trulydegraded - (ml gas volume x 2.2)

PF= mg substrate truly degraded /vol of gas ml ↑PF- ↑DMI, ↓CH4 Forages with high voluntary DMI have high gas

volumes at early incubation times (i.e., 2-8 h) andhigh substrate true degradabilities but low gasproduction at later times of incubation

KINETICS OF FERMENTATION

The pattern of fermentation influence intake

Allows recording of gasproduced at several timeswhich is used to predict therate at which feed is digested

The gas method has beenused to evaluate the effects ofgrain processing on the rateand extent of gas production.•

Allows recording of gasproduced at several timeswhich is used to predict therate at which feed is digested

The gas method has beenused to evaluate the effects ofgrain processing on the rateand extent of gas production.•

STOICHIOMETRIC CALCULATION OF METHANE FROM VFAPRODUCTION

Fermentative CO2 = (A/2) + (P/4) + 1.5B

Fermentative CH4 = (A+2B)- CO2

(Where A= moles of acetate; B= moles of propionate; C= moles of butyrate)

((BlümmelBlümmel et al.,et al., 19971997 andand GetachewGetachew et al.,et al., 1998)1998)

EFFECT OF ANTI NUTRITIVE FACTOR

The effect of tannins on the nutritive value offeeds can be studied using tannin-bindingagents, such as polyethylene glycol (PEG),which strongly binds to tannins and inhibitstheir biological effects.

The percent increase in gas production whenPEG is present indicates the rate at whichtannins depress rumen fermentation of feeds

The effect of tannins on the nutritive value offeeds can be studied using tannin-bindingagents, such as polyethylene glycol (PEG),which strongly binds to tannins and inhibitstheir biological effects.

The percent increase in gas production whenPEG is present indicates the rate at whichtannins depress rumen fermentation of feeds

EFFECT OF RUMEN MODIFIER

Used to study the effect of feed additives/rumen modifier on rumen fermentationpattern

Compounds fed to stimulate fibre degradationor methane inhibition, protein protectionmay be studied

Used to study the effect of feed additives/rumen modifier on rumen fermentationpattern

Compounds fed to stimulate fibre degradationor methane inhibition, protein protectionmay be studied

RATION BALANCING/ ASSOCIATIVE EFFECTS

Currently being used to assess “associative” effects offeeds used in rations

Energy value of a ration- adding up energy values ofthe individual feeds in the ration → assumption,individual energy value of any particular feed samein every possible combination with other feeds

WS ↓ Digestibility → WS+N2 (Urea/Protein)→↑Digestibility ↑ energy value

WS+ Leaves ↑ Digestibility

Currently being used to assess “associative” effects offeeds used in rations

Energy value of a ration- adding up energy values ofthe individual feeds in the ration → assumption,individual energy value of any particular feed samein every possible combination with other feeds

WS ↓ Digestibility → WS+N2 (Urea/Protein)→↑Digestibility ↑ energy value

WS+ Leaves ↑ Digestibility

Monitoring rumen microbial change-used to study substrate related factors thatinfluence microbial populations in the rumen→ enables manipulation of rumen microflorato increase the utilization of feeds

Evaluation of genetically modified feedsfor their nutritive value

Monitoring rumen microbial change-used to study substrate related factors thatinfluence microbial populations in the rumen→ enables manipulation of rumen microflorato increase the utilization of feeds

Evaluation of genetically modified feedsfor their nutritive value

CONCLUSION

IVGPT - simple technique of measuring gas andmicrobial mass to be a routine and powerful toolfor feed evaluation thus avoiding the need fortime-consuming, laborious and expensivefeeding studies

IVGPT - simple technique of measuring gas andmicrobial mass to be a routine and powerful toolfor feed evaluation thus avoiding the need fortime-consuming, laborious and expensivefeeding studies

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