The objective of this study was to provide estimates of the impact of trait genetic gains on methane emissions from NZ dairy and beef farms. The effect of each trait on gross emissions (GE) and emissions intensity (EI) was modelled by estimating effects of trait changes on per-animal feed consumption and the associated methane production, per-animal production and numbers of animals in the system. In dairy, the annual gross emissions per breeding cow associated with genetic change were estimated to increase for all traits except Residual Survival and Fertility. Conversely, emission intensity values were estimated to decrease for Milk Fat, Milk Protein, Milk Solids, Residual Survival, Fertility and Body-condition Score (BCS) as genetic merit improves. In beef production, increases in genetic merit for cow mature weight, cow BCS, cow calving ease and heifer pregnancy were estimated to increase the annual gross emissions per breeding cow. Conversely, an increase in merit associated with stayability and gestation length reduced annual gross emissions per breeding cow. The effect of increasing carcase weight on gross emissions depended on whether the faster growth performance was used to slaughter the animal earlier, or to take the animal through to heavier finishing weights. Keywords: methane; emissions intensity; gross emissions; dairy; beef
New Zealand Journal of Animal Science and Production, Volume 80, Online, 76-79, 2020
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