Development of a software model to estimate daily greenhouse gas emissions of pasture-fed ruminant farming systems

Abstract

A software model has been developed to estimate greenhouse gas emissions of pasture-fed ruminant farming systems. The model estimates on-farm emissions associated with livestock (sheep and beef), fertiliser, petrol, diesel and electricity. Carbon sequestration from native and exotic forestry is then included to produce an on-farm carbon footprint, in the form of carbon dioxide equivalents. This paper describes the livestock model, which has been designed to record the movement of animals within individual farm units according to defined livestock classes. Allowances are made for unrecorded deaths, by estimating the number of animals missing within a defined time period and spreading the deaths according to expected seasonal variation in mortality. The enteric methane and nitrous oxide emissions are predicted using a combination of customised growth and lactation curves, and internationally recognised formulae to predict nutrient energy requirements. Customised growth and lactation curves allow estimation of liveweights and energy requirements associated with maintenance, growth, pregnancy and lactation on a daily basis. Daily estimation of emissions reduces errors introduced by monthly or seasonal averaging of livestock numbers and liveweights. The model has been developed into a commercial application (Alliance Group hoofprint) for use by New Zealand sheep and beef farmers, and could be adapted for other international livestock farming operations.