Discipline: environment; Keywords: carbon footprint, dairy, dilution of maintenance, environmental impact, greenhouse gas, productive efficiency.
The environmental impact of producing animal source foods is a critical topic of policy discussion in domestic and international governments, social media, the popular press, and the consumer marketplace. Livestock’s contribution to the environmental impacts associated with food production are significant concerns for all food chain stakeholders, including livestock producers who play a major role in reducing environmental impacts per unit of food. The environmental impacts of improving livestock productivity have been demonstrated in multiple studies, ranging from historical analyses of the impacts of improving dairy cattle productivity. However, point-in- time estimates become dated very quickly, yet continue to be widely cited, often leading to incorrect conclusions regarding progress to reduce environmental impacts of food production. The U.S. dairy industry considerably reduced environmental impacts between 1944 and 2007, primarily through improved dairy cow productivity. However, although milk yield per cow has increased over the past decade, whole-system environmental impact analyses have not been conducted over this time period, Therefore, the objective of the study by Drs J.l. Capper and R.A. Cady was to compare the environmental impact of U.S. dairy cattle production in 2007–2017. Their results were published in the Journal of Animal Science, Volume 98 of 2020, page 1 to 14. The title of the paper is: The effects of improved performance in the U.S. dairy cattle industry on environmental impacts between 2007 and 2017.
A deterministic model based on population demographics, metabolism, and nutrient requirements of dairy cattle was used to estimate resource inputs, nutrient excretion, and greenhouse gas (GHG) emissions per 1.0 × 106 t (one million metric t or MMT) of energy-corrected milk (ECM) produced in 2007 and 2017. System boundaries extended from the manufacture and transport of cropping inputs to milk at the farm gate. Milk transport, processing, and retail were not included. Dairy systems were modelled using typical management practices, herd population dynamics, and production data from U.S. dairy farms. Cropping data were sourced from national databases.
The results show that the resources required to produce 1.0 MMT ECM in 2017 were considerably reduced relative to those required in 2007, with 2017 production systems using 74.8% of the cattle, 82.7% of the feedstuffs, 79.2% of the land, and 69.5% of the water as compared to 2007. Waste outputs were similarly reduced, with the 2017 U.S. dairy industry producing 79.4%, 82.5%, and 85.7% of the manure, N, and P excretion, respectively. Dairy production in 2017 emitted 80.9% of the methane and 81.5% of the nitrous oxide per 1.0 MMT ECM compared to 2007. Enteric and manure emissions contributed the major proportion (80%) of GHG emissions per unit of milk, with lesser contributions from cropping (7.6%) and fertilizer application (5.3%). The GHG emissions per 1.0 MMT ECM produced in 2017 were 80.8% of equivalent milk production in 2007. Consequently, although total U.S. ECM production increased by 24.9% between 2007 and 2017 and per cow from 9 150 to 11 195 kg ECM per year, the total GHG emissions from this milk production increased by only 1.0%.
The authors concluded that in line with previous historical analyses, the U.S. dairy industry has made remarkable productivity gains and environmental progress over time. To maintain this culture of continuous improvement, the US dairy industry have to build on the gains made to date and demonstrate its commitment to reducing environmental impacts, while improving both economic viability and social acceptability.