ghg-inventory-1990-2013

performed on a monthly basis. The equation below is derived from the general equation
used in the Australian feeding standards and adjusted to suit New Zealand conditions.
This method includes a maintenance requirement (a function of the animal’s liveweight
and stage of maturity), a production energy requirement needed for a given level of
productivity (milk yield and liveweight gain), physiological state (eg, pregnant or
lactating), and the amount of energy expended on the grazing process):
0.1
Where: ME BASAL is the energy requirement for maintenance,
ME P is the energy used directly for production (meat, milk, wool, gestation etc),
and,
ME GRAZE is the additional energy required by grazing livestock.
Thus:
0.28. exp0.03
0.1
Where: K, S and M are constants defined in CSIRO (1990); K = 1.0 for sheep and 1.4
for cattle, S = 1.0 for females and castrates and 1.15 for entire males, M = 1 for
all animals except milk-fed animals. M has been removed from the New
Zealand calculations and an adjustment for milk-fed animals is carried out
through a milk adjustment factor detailed later.
W is the live weight (kg),
A is the age in years, up to a maximum value of 6,
k m is the net efficiency of use of ME for maintenance, and,
E GRAZE is the additional energy expenditure of livestock in cold stress.
The CSIRO (1990) algorithms take into account animal liveweight and production
requirements based on the rate of liveweight gain, sex, milk yield and physiological state.
For further details, see the Inventory methodology document of Pickering and Wear
(2013), which is available on the Ministry for Primary Industries website
(http://mpi.govt.nz/news-and-resources/statistics-and-forecasting/greenhouse-gasreporting/).
Monthly diet energy (E) concentration: Dairy cattle, non-dairy cattle, sheep and deer
are predominantly fed on pasture year round. Datasets of estimated monthly
energy concentrations of pasture consumed by different livestock are used for all years.
These data are reported in the Inventory methodology document (Pickering and
Wear, 2013, appendices 3, 9 and 19, http://mpi.govt.nz/news-and-resources/statistics-andforecasting/greenhouse-gas-reporting/).
There are no comprehensive published data
available that allow the estimation of a time series dating back to 1990. The data used are
derived from published and unpublished research trial data, and supplemented with
additional data from farm surveys on commercial cattle and sheep farms.
Bown et al, 2013, were commissioned to review and collate data held around
New Zealand on the energy and nitrogen content of pasture. Pasture measurements from
eight research studies and a commercial testing laboratory were collated, analysed and
compared with the national monthly average values used in the current Inventory model.
The collated database (defined as the ‘Global database’ in figure 5.1.4) was collected
from 1996 to 2011 from dairy cattle, non-dairy cattle and sheep farms all over
New Zealand. The graph in figure 5.1.4 shows, as an example using the dairy farm data,
how the assumed values in the New Zealand Inventory for energy in dairy pasture
compare with 2,371 dairy pasture samples from the Global database, and that they are in
reasonable agreement.
126 New Zealand’s Greenhouse Gas Inventory 1990–2013