Skip to contents

Calculate methane conversion factor (ym)

Source: R/core_model_emissions_enteric.R
calc_conversion_factor_ym.Rd

Calculates the methane conversion factor (ym, % of dietary gross energy in feed converted to methane) for a given species and cohort based on diet digestibility. Implements species- and cohort-specific rules consistent with IPCC Tier 2 approach.

Usage

calc_conversion_factor_ym(
  species_short,
  cohort_short,
  ration_digestibility_fraction
)

Arguments

species_short

Character. Code identifying the livestock species. Supported values include:

  • PGS: pigs

  • CML: camels

  • CTL: cattle

  • BFL: buffalo

  • SHP: sheep

  • GTS: goats

cohort_short

Character. Sex- and age-specific cohort code describing the production stage of the animals. Supported values include:

  • FA: adult females (from age at first parturition)

  • FS: sub-adult females (from weaning to age at first parturition)

  • FJ: juvenile females (from birth to weaning)

  • MA: adult males (from age at first breeding)

  • MS: sub-adult males (from weaning to age at first breeding)

  • MJ: juvenile males (from birth to weaning)

ration_digestibility_fraction

Numeric. Average digestibility of the feed ration, expressed as ratio of digestible (or metabolizable, for poultry) to gross energy content (fraction).

Value

Numeric. Methane (CH4) conversion factor (ym), representing the percentage of gross energy of the feed ration that is converted to CH4 (percentage).

Details

ym is computed using species- and cohort-specific default relationships with diet digestibility (Opio et al., 2013).

ration_digestibility_fraction can be calculated with calc_ration_digestibility - see also run_ration_quality_module.

  • For CTL and BFL: $$ym = 9.75 - 0.05 \times (ration\_digestibility\_fraction \times 100)$$

  • For SHP, GTS and CML:

    • FA and MA cohorts: $$ym = 9.75 - 0.05 \times (ration\_digestibility\_fraction \times 100)$$

    • FS and MS cohorts: $$ym = 7.75 - 0.05 \times (ration\_digestibility\_fraction \times 100)$$

  • For PGS: ym is assigned fixed values by cohort:

    • FA and MA cohorts: $$ym = 1.01$$

    • FS and MS cohorts: $$ym = 0.39$$

ym is returned as 0 for juvenile cohorts (FJ, MJ), assuming negligible enteric methane production before weaning/rumen development.

This function is part of the run_emissions_enteric_module().

References

Opio, C., Gerber, P., Mottet, A., Falcucci, A., Tempio, G., MacLeod, M., Vellinga, T., Henderson, B. & Steinfeld, H. (2013). Greenhouse gas emissions from ruminant supply chains – A global life cycle assessment. Food and Agriculture Organization of the United Nations (FAO), Rome.

Jørgensen, H., Theil, P. K. & Knudsen, K. E. B. (2011). Enteric methane emission from pigs. In: Planet Earth 2011 – Global Warming Challenges and Opportunities for Policy and Practice (p. 610; Table 2). InTech.

IPCC. (2019). 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Chapter 10: Emissions from Livestock and Manure Management, Equation 10.21.

IPCC. (2006). 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Chapter 10: Emissions from Livestock and Manure Management, Equation 10.21.

See also

run_emissions_enteric_module, calc_ration_digestibility, run_ration_quality_module