Abstract
Global demand for livestock products is rising, resulting in a growing demand for feed and potentially burdening freshwater resources to produce this feed. To offset this increased pressure on water resources, the environmental performance of livestock sector should continue to improve. Over the last few decades, product output per animal and feedstuff yields in the US have improved, but before now it was unclear to what extent these improvements influenced the water productivity (WP) of the livestock products. In this research, we estimate changes in WP of animal products from 1960 to 2016. We consider feed conversion ratios (dry matter intake per head divided by product output per head), feed composition per animal category, and estimated the water footprint of livestock production following the Water Footprint Network's Water Footprint Assessment methodology. The current WP of all livestock products appears to be much better than in 1960. The observed improvements in WPs are due to a number of factors, including increases in livestock productivity, feed conversion ratios and feed crop yields, the latter one reducing the water footprint of feed inputs. Monogastric animals (poultry and swine) have a high feed-use efficiency compared to ruminants (cattle), but ruminants consume relatively large portion of feed that is non-edible for humans. Per unit of energy content, milk has the largest WP followed by chicken and pork. Per gram of protein, poultry products (chicken meat, egg and turkey meat) have the largest WP, followed by cattle milk and pork. Beef has the smallest WP. These data provide important information that may aid the development of strategies to improve WP of the livestock sector.
Highlights
The world population is expected to reach 9.8 billion by 2050 (UNDESAPD, 2017) with much of the growth taking place in urban areas
The result from the current study can be compared with values found in the literature at three levels: feed conversion ratios, total feed requirement, and the water productivity (WP) of livestock products (Table 5)
The feed conversion ratios and the total feed values estimated in the current study are very close to the values from literature
Summary
The world population is expected to reach 9.8 billion by 2050 (UNDESAPD, 2017) with much of the growth taking place in urban areas. Driven by growing population, increasing income, and urbanization, the demand for livestock products in 2050 will increase by 35% from its 2016 level (Alexandratos and Bruinsma, 2012; FAO, 2017). The livestock sector contributes about 36% to the gross value of agricultural production (Alexandratos and Bruinsma, 2012), supports the livelihood of farmers and provides traction power for ploughing in smallholder crop production systems (Steinfeld and Gerber, 2010; Thornton, 2010). Unless proper policies targeting production systems and consumption trends are put in place, the growth in the livestock sector could put further pressure on already strained natural resources such as freshwater and land, and aggravate land degradation, water pollution, and greenhouse gas emissions. Various studies have highlighted the environmental impacts of the livestock sector including water consumption and pollution (Beckett and Oltjen, 1993; Capper, 2011; Deutsch et al, 2010; Mekonnen and Hoekstra, 2012; Steinfeld et al, 2006), nutrient emission (Bouwman et al, 2013; Capper, 2011; Galloway et al, 2010; Mekonnen and Hoekstra, 2015, 2018; Pelletier and Tyedmers, 2010), climate change (Gerber et al, 2013; Pelletier and Tyedmers, 2010; Steinfeld et al, 2006), and appropriation of biomass (Pelletier and Tyedmers, 2010; Wirsenius, 2003)
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