First results of a meta-analysis of the methane emission data of New Zealand ruminants

In New Zealand (NZ), 49% of the country's total greenhouse gas emissions are non-carbon dioxide emissions from the agricultural section. Ruminant livestock (predominantly cattle and sheep) are the primary sources of NZ's methane (CH4) emissions. The large majority of these ruminants are kept in a grazing system. With the introduction of the ERUCT technique (Emissions from Ruminants Using a Calibrated Tracer) in 1996, it became possible to collect CH4 emission data from NZ's grazing ruminants. A first statistical analysis of data collected in a “Methane Research Database” was carried out using four groups of data, female cattle (n = 738), male cattle (n = 72), female sheep (n = 90) and male sheep (n = 125), respectively. Regression equations were calculated based on the animals' estimated dry matter intake (EDMI), neutral detergent fibre (NDF) intake or metabolic live weight (MLW). For female animals, R2 of these equations lay below 0.30. However, for male animals, equations based on MLW gave promising R2 of 0.67 (cattle) or 0.44 (sheep). Group means are given for daily CH4 emission, EDMI and live weight as well as CH4 ratios (g/kg EDMI and g/kg0.75 MLW). For dairy cows the CH4 emission was also related to the animals' milk yield.