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Calculate metabolic energy requirements for pregnancy

Source: R/core_model_metabolic_energy_req.R
calc_metabolic_energy_req_pregnancy.Rd

Calculates the energy requirement for pregnancy by cohort (MJ/head/day) for pregnant females, defined as the additional energy needed to support gestation.

Usage

calc_metabolic_energy_req_pregnancy(
  species_short,
  cohort_short,
  metabolic_energy_req_maintenance = NA_real_,
  parturition_rate = NA_real_,
  litter_size = NA_real_,
  pregnancy_duration = NA_real_,
  non_productive_duration = NA_real_,
  lactation_duration = NA_real_,
  cohort_duration_days = NA_real_,
  offtake_rate = 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)

metabolic_energy_req_maintenance

Numeric. Energy required for maintenance, defined as the amount of energy needed to keep the animal at equilibrium such that body energy is neither gained nor lost. Expressed as net energy for CTL, BFL, SHP, GTS and as metabolizable energy for CML and PGS (MJ/head/day).

parturition_rate

Numeric. Average annual number of parturitions per female animal (# parturitions/adult female/year). A herd-level reproductive performance indicator calculated as the total number of parturitions (deliveries) occurring during a year divided by the number of adult females potentially able to give birth during that year.

litter_size

Numeric. Average number of offspring born per parturition (# offspring/parturition). This value can be calculated as the total number of offspring born divided by the total number of parturitions during the year.

pregnancy_duration

Numeric. Duration of pregnancy period (days).

non_productive_duration

Numeric. Period during which the animal is not performing any productive physiological function such as pregnancy or lactation (days). Required only for PGS.

lactation_duration

Numeric. Duration of the lactation period, defined as the number of days during which the animal is lactating (days). Required only for PGS.

cohort_duration_days

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

offtake_rate

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

Value

Numeric. Energy required for pregnancy for pregnant females (MJ/head/day). Expressed as net energy for CTL, BFL, SHP, GTS and as metabolizable energy for CML and PGS.

Details

This component follows the IPCC Tier 2 partitioning framework and is applied only to female cohorts (FA and FS).

Pregnancy energy (metabolic_energy_req_pregnancy) represents the additional energy required to support gestation. Requirements are computed as a fraction of maintenance energy and are adjusted to reflect reproductive activity within the cohort:

  • For FA, requirements are scaled by the annual parturition rate (parturition_rate) and (when applicable) by the fraction of the reproductive cycle spent in gestation (pregnancy_duration/(pregnancy_duration+lactation_duration+non_productive_duration)).

  • For FS, only a fraction of animals is assumed to reach reproductive age within the cohort; requirements are therefore scaled by the proportion remaining in the cohort (\(1 - offtake\_rate\)) and by the share of the cohort duration spent pregnant (pregnancy_duration/cohort_duration_days).

General form $$ metabolic\_energy\_req\_pregnancy = metabolic\_energy\_req\_maintenance \times c_{preg} \times S $$

where

  • \(c_{preg}\) is a species-specific pregnancy coefficient,

  • \(S\) is a scaling term that depends on cohort (FA vs FS).

  • \(metabolic\_energy\_req\_maintenance\) can be calculated using calc_metabolic_energy_req_maintenance()

Specific coefficients by species and cohort:

  • CTL and BFL (IPCC, 2006, 2019): Pregnancy energy is approximated as \(10\%\) of maintenance energy.

    • FA: $$ \begin{aligned} metabolic\_energy\_req\_pregnancy &= 0.10 \times metabolic\_energy\_req\_maintenance \times parturition\_rate \times \\ & \frac{pregnancy\_duration}{365} \end{aligned} $$

    • FS: $$ \begin{aligned} metabolic\_energy\_req\_pregnancy &= 0.10 \times metabolic\_energy\_req\_maintenance \times \\ & \frac{pregnancy\_duration}{cohort\_duration\_days} \times (1 - offtake\_rate) \end{aligned} $$

  • CML (Wardeh, 2004): Pregnancy energy is estimated as \(12\%\) of maintenance energy.

    • FA: $$ metabolic\_energy\_req\_pregnancy = 0.12 \times metabolic\_energy\_req\_maintenance \times parturition\_rate $$

    • FS: $$ metabolic\_energy\_req\_pregnancy = 0.12 \times metabolic\_energy\_req\_maintenance \times \frac{pregnancy\_duration}{cohort\_duration\_days} \times (1 - offtake\_rate) $$

  • SHP and GTS (IPCC 2006; 2019): Pregnancy energy is calculated as a litter-size-dependent fraction of maintenance energy (\(c_{preg}\)).

    • FA: $$ \begin{aligned} metabolic\_energy\_req\_pregnancy &= metabolic\_energy\_req\_maintenance \times c_{preg} \times parturition\_rate \times \\ & \frac{pregnancy\_duration}{365} \end{aligned} $$ where \(c_{preg}\) is: $$ c_{preg} = \left\{ \begin{array}{ll} 0.077 \times (2 - litter\_size) + 0.126 \times (litter\_size - 1), & 1 \le litter\_size \le 2 \\ 0.150, & litter\_size > 2 \end{array} \right. $$

    • FS: A single-birth coefficient is used (\(c_{preg}=0.077\)) and scaled by the proportion of reproductive individuals in the cohort: $$ \begin{aligned} metabolic\_energy\_req\_pregnancy &= 0.12 \times metabolic\_energy\_req\_maintenance \times \\ & \frac{pregnancy\_duration}{cohort\_duration\_days} \times \\ & (1 - offtake\_rate) \end{aligned} $$

  • PGS (NRC, 1998): Pregnancy energy is expressed using a gestation coefficient \(c_{gest}\) (MJ/piglet), with default \(c_{gest}=0.14985\).

    • FA: $$ \begin{aligned} metabolic\_energy\_req\_pregnancy &= c_{gest} \times litter\_size \times \\ & \frac{pregnancy\_duration}{ non\_productive\_duration + pregnancy\_duration + lactation\_duration } \end{aligned} $$

    • FS: $$ \begin{aligned} metabolic\_energy\_req\_pregnancy &= c_{gest} \times litter\_size \times \\ & \frac{pregnancy\_duration}{cohort\_duration\_days} \times \\ & (1 - offtake\_rate) \end{aligned} $$

This function is part of the run_metabolic_energy_req_module().

References

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

IPCC. (2019). 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Chapter 10: Emissions from Livestock and Manure Management, Equation 10.13; Table 10.7.

IPCC. (2006). 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Chapter 10: Emissions from Livestock and Manure Management, Equation 10.13; Table 10.7.

Wardeh, M. F. (2004). The nutrient requirements of the dromedary camel. Journal of Camel Science, 1(1):37-45. The Camel Applied Research and Development Network (CARDN), Arab Center for the Studies of Arid Zones and Dry Lands (ACSAD).

See also

run_metabolic_energy_req_module, calc_metabolic_energy_req_maintenance