Exploring the impact of replacement rates on carbon footprint in south-east Australian dairy herds

Context Greater replacement rates in dairy herds lead to increased costs for rearing and/or purchasing replacement heifers and greater herd greenhouse gas (GHG) emissions. Aims This study aimed to estimate current GHG emissions and potential improvements in net farm emissions (NFE) and emission intensity (EI) by reducing replacement rates (percentage of calvings in the herd in the year that were by first calving heifers) using a series of eight case study farms. Methods The research was conducted by modelling eight Australian case study farms (five from northern Victoria/southern New South Wales and three from the Gippsland region) using farm-specific data. Data included herd structure, milk production, feed quality and quantity, and energy, fuel, and fertiliser usage. GHG emissions were estimated using the Dairy GHG Accounting Framework tool (ver. 14.5), calculating NFE and EI in megagram of carbon dioxide equivalents (Mg CO2e) and kilograms of carbon dioxide equivalent per kilogram of milk solids (kg CO2e/kg MS). The study modelled reducing the replacement rate by 5, 10, and 15 percentage points. Key results The average (±s.d.) EI per kilogram of MS for the eight case study farms was 15.8 ± 3.5 kg CO2e/kg MS. A 15-percentage point reduction in replacement rate was estimated as leading to reductions in EI per kilogram of MS ranging from 0.9 to 1.7 kg CO2e/kg MS across the case-study farms. However, NFEs were estimated as increasing with reductions in replacement rate for five of the eight case study farms. Conclusions Reducing the replacement rate can reduce EI (measured in kg CO2e/kg MS) but increase NFEs. Implications The findings underscore the importance of considering both environmental factors, such as GHG emissions, and economic aspects, such as net farm income, when evaluating and implementing strategies for sustainable dairy farming.