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Calculate metabolic energy requirements for lactation

Source: R/core_model_metabolic_energy_req.R
calc_metabolic_energy_req_lactation.Rd

Calculates the energy requirement for lactation by cohort (MJ/head/day), defined as the energy needed to support milk production by lactating females.

Usage

calc_metabolic_energy_req_lactation(
  species_short,
  cohort_short,
  lactating_females_fraction = NA_real_,
  milk_yield_day = NA_real_,
  milk_fat_fraction = NA_real_,
  non_productive_duration = NA_real_,
  pregnancy_duration = NA_real_,
  litter_size = NA_real_,
  death_rate_juvenile = NA_real_,
  live_weight_at_birth = NA_real_,
  live_weight_at_weaning = NA_real_,
  lactation_duration = NA_real_,
  parturition_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)

lactating_females_fraction

Numeric. Proportion of adult females that are lactating during the assessment period (fraction). Required only for species = CML, CTL, BFL, SHP, and GTS.

milk_yield_day

Numeric. Average milk yield per milk-producing animal during the assessment duration (kg/head/day). This value is calculated as the total quantity of milk produced for human consumption by milk-producing animals during the assessment period, divided by the number of milk-producing animals, and the length of the assessment period (days). Required only for species = CML, CTL, BFL, SHP, and GTS.

milk_fat_fraction

Numeric. Milk fat fraction (kg fat/kg milk). Required only for species = CML, CTL, BFL, SHP, and GTS.

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.

pregnancy_duration

Numeric. Duration of pregnancy period (days).

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.

death_rate_juvenile

Numeric. Fraction of deaths in a herd over a year for juvenile cohorts (i.e. FJ and MJ), (fraction).

live_weight_at_birth

Numeric. Live weight of the animal at birth (kg).

live_weight_at_weaning

Numeric. Live weight of the animal at weaning (kg).

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.

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.

Value

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

Details

This approach follows the IPCC Tier 2 partitioning method and applies species-specific equations for lactation energy requirements as a function of the quantity of milk produced and a species-specific energy cost per unit of milk.

Requirements are calculated only for cohort = FA (adult females) and are scaled by the proportion of lactating animals (lactating_females_fraction) or reproducing females (parturition_rate) within the cohort.

Species-specific approach:

CTL, BFL, CML, SHP and GTS:

Total milk production includes:

  • milk extracted for human consumption (milk_yield)

  • milk consumed directly by offspring (milk_for_offspring)

In general form, lactation energy is computed as:

$$ metabolic\_energy\_req\_lactation = (milk\_yield \times lactating\_females\_fraction + milk\_for\_offspring) \times energy\_milk $$

where:

energy_milk is a species-specific coefficient representing the net energy cost of producing one kilogram of milk (MJ/kg milk).

Species-specific values of energy_milk are:

  • CTL, BFL: estimated as a function of milk fat content, \(1.47 + 0.40 \times (milk\_fat\_fraction \times 100)\) (NRC, 1989),

  • CML: \(4.063\) (Wardeh, 2004),

  • SHP: \(4.6\) (AFRC, 1993),

  • GTS: \(3.0\) (AFRC, 1998).

milk_for_offspring is the daily amount of milk required to rear offspring across the year (kg/day). It is calculated assuming that 5 kg of milk are required for each kilogram of live-weight gain up to weaning:

$$ milk\_for\_offspring = \frac{parturition\_rate \times 5 \times (weaning\_weight - birth\_weight)}{365} $$

For SHP and GTS, milk_for_offspring is multiplied by litter_size to account for multiple offspring per birth.

PGS (NRC, 1998):

Lactation energy accounts only for the milk consumed directly by offspring (milk_for_offspring), adjusted by the fraction of the reproductive cycle spent in lactation (cadj):

$$ \begin{aligned} metabolic\_energy\_req\_lactation &= litter\_size \times (1 - 0.5 \times death\_rate\_juvenile) \times \\ & \left( \frac{0.02059 \times (weaning\_weight - birth\_weight) \times 1000} {lactation\_duration} - \frac{0.3766}{0.67} \right) \times cadj \end{aligned} $$

where:

  • \(0.02059\) is the coefficient for lactation energy requirement (MJ/g live weight),

  • \(0.3766\) is the coefficient for sow weight loss during lactation (MJ/head/day),

  • \(0.67\) is the efficiency of conversion of dietary intake to milk energy (fraction),

  • \(cadj\) is the fraction of the reproductive cycle spent in lactation:

    $$ cadj = \frac{lactation\_duration}{non\_productive\_duration + pregnancy\_duration + lactation\_duration} $$

This function is part of the run_metabolic_energy_req_module().

References

AFRC (1998) The Nutrition of Goats. CAB International, Wallingford, UK.

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.

IPCC. (2019). 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Chapter 10: Emissions from Livestock and Manure Management, Equation 10.8-10.10.

IPCC. (2006). 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Chapter 10: Emissions from Livestock and Manure Management, Equation 10.8-10.10.

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

NRC (1989) Nutrient Requirements of Dairy Cattle, 6th Ed. . Washington, D.C. U.S.A: National Academy Press.

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