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Calculate metabolic energy requirements for growth

Source: R/core_model_metabolic_energy_req.R
calc_metabolic_energy_req_growth.Rd

Calculates the energy requirement for growth by cohort (MJ/head/day), defined as the energy required for body tissue accretion, corresponding to the retained energy component of live weight gain.

Usage

calc_metabolic_energy_req_growth(
  species_short,
  cohort_short,
  live_weight_cohort_average = NA_real_,
  live_weight_cohort_final = NA_real_,
  live_weight_cohort_initial = NA_real_,
  live_weight_mature_stage = NA_real_,
  daily_weight_gain = NA_real_,
  offtake_rate = NA_real_,
  cohort_duration_days = NA_real_
)

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)

live_weight_cohort_average

Numeric. Average live weight over the cohort stage. Computed by accounting for the share of offtaken animals within the cohort, using their slaughter weight, and the potential final weight of animals that remain in the cohort (kg).

live_weight_cohort_final

Numeric. Live weight at the end of the cohort stage, accounting for both surviving and offtaken animals. Computed as a weighted average of the potential final weight of surviving animals and the slaughter weight of offtaken animals, based on the offtake rate (kg).

live_weight_cohort_initial

Numeric. Live weight at the beginning of the cohort stage (kg).

live_weight_mature_stage

Numeric. Mature (adult) live weight that the animal can attain under given biological and management conditions (kg).

daily_weight_gain

Numeric. Average live weight gain of the cohort over the cohort stage (kg/head/day).

offtake_rate

Numeric. Annual proportion of animals removed from the herd for each sex-age cohort (fraction).

cohort_duration_days

Numeric. Amount of time that each animal spends in a specific cohort (days).

Value

Numeric. Energy required for growth (i.e., weight gain) (MJ/head/day). Expressed as net energy for CTL, BFL, SHP, GTS and as metabolizable energy for CML and PGS.

Details

This function follows the IPCC Tier 2 energy partitioning approach and applies species-specific equations for growth energy requirements.

In general, growth energy is computed only for growing cohorts (FJ, FS, MJ, MS); in this implementation, growth is set to 0 for adult cohorts (FA, MA).

Species-specific approach:

  • CTL and BFL (NRC, 1996; IPCC, 2006; IPCC, 2019)

    Growth energy is computed using a growth coefficient \(cgro\) that differs between castrated and intact males. For male cohorts, \(cgro\) is calculated as a weighted average using offtake_rate, assuming that animals removed from the herd are castrated and animals remaining in the cohort are intact.

  • SHP and GTS (Gibbs et al., 2002; AFRC, 1993; IPCC, 2006; IPCC, 2019)

    For sheep and goats, growth energy is calculated using a linear formulation with coefficients \(a\) and \(b\) (MJ/kg live weight). For male cohorts, the coefficients differ between castrated and intact males; the model computes a weighted average using offtake_rate, assuming that offtaken animals are castrated.

  • CML (Al-Jassim, 2019)

    Growth energy is represented using a simplified linear relationship with daily weight gain.

  • PGS (NRC, 1998)

    For pigs, growth is assumed to consist exclusively of protein tissue and fat tissue, and growth energy requirements are expressed as metabolizable energy (ME).

    The growth energy coefficient \(cgro\) (MJ/kg live weight) is calculated as:

    \( cgro = prot\_tissue\_frac \times meat\_protein \times meat\_protein\_energy + (1 - prot\_tissue\_frac) \times fat\_adipose\_tissue_frac \times meat\_fat\_energy \)

    Total metabolizable energy required for growth is then:

    \(metabolic\_energy\_req\_growth = daily\_weight\_gain \times cgro\)

    where:

    • \(cgro\) is the growth energy coefficient (MJ/kg live weight),

    • prot_tissue_frac = 0.65 is the fraction of protein tissue in daily weight gain,

    • meat_protein = 0.23 is the fraction of protein in protein tissue,

    • meat_protein_energy = 54.0 is the ME cost of protein deposition (MJ/kg protein),

    • fat_adipose_tissue_frac = 0.90 is the fraction of fat in adipose tissue,

    • meat_fat_energy = 52.3 is the ME cost of fat deposition (MJ/kg fat).

This function is part of the run_metabolic_energy_req_module().

References

Al-Jassim, R. (2019). Metabolisable energy and protein requirements of the Arabian camel (Camelus dromedarius). Journal of Camelid Science (12) 33-45

NRC (1998). Nutrient Requirements of Swine, 10th Revised Edition. National Academies Press, Washington, DC.

NRC (1996). Nutrient Requirements of Beef Cattle, 7th Revised Edition. National Academies Press, Washington, DC.

AFRC (1993). Energy and Protein Requirements of Ruminants. An Advisory Manual Prepared by the AFRC Technical Committee on Responses to Nutrients. CAB International, Wallingford, UK.

Gibbs, M.J., Conneely, D., Johnson, D., Lassey, K.R. and Ulyatt, M.J. (2002). CH4 emissions from enteric fermentation. In: Background Papers: IPCC Expert Meetings on Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories, p 297–320. IPCC-NGGIP, Institute for Global Environmental Strategies (IGES), Hayama, Kanagawa, Japan.

IPCC. (2019). 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Chapter 10: Emissions from Livestock and Manure Management, Equation 10.6 and 10.7; Table 10.6.

IPCC. (2006). 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Chapter 10: Emissions from Livestock and Manure Management, Equation 10.6 and 10.7; Table 10.6.

See also

run_metabolic_energy_req_module, calc_cohort_weights, calc_avg_weights, calc_daily_weight_gain