Agriculture Reference
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efficiency of plant-derived feedstuffs to animal
products. For example, among animal prod-
ucts evaluated the water footprints of meat
production increased more than 3.5-fold;
from chicken meat (4300 m 3 t −1 ), to goat meat
(5500 m 3 t −1 ), to pig meat (6000 m 3 t −1 ); and
sheep meat (10,400 m 3 t −1 ) to beef (15,400 m 3 t −1 ).
This wide range is explained partially by differ-
ences in feed conversion efficiencies. Pooled
across the production system types (grazing,
mixed crop-animal and industrial), eight times
more feed dry matter was required per unit of
beef meat produced compared with pig meat,
and 11 times more than for chicken meat pro-
duction. Besides the poorer feed conversion
efficiency, obviously the composition of the
diets (e.g. more fibrous feeds for ruminants,
which are not utilizable by non-ruminants)
differed appreciably among the animal species
and system types. The 'overall global diet' was
composed of a much greater proportion of
concentrate feeds for broiler chickens (73%)
compared with beef cattle (only 5%).
Additionally, from a freshwater perspective,
animal products from grazing systems had
smaller footprints than from industrial animal
systems mainly because of less use of ground-
and surface water. Also, within the four coun-
tries examined, less freshwater (called grey
water) was required in the grazing system com-
pared with the mixed or industrial systems to
sufficiently assimilate (dilute) pollutants to meet
water quality standards. Overall, model predic-
tions clearly showed that it was a more efficient
use of water to produce edible calories, protein
and fat through crop production than through
animal production (Mekonnen and Hoekstra,
Pooled across animal production system
types in the four countries, total water footprint
(the sum of precipitation, surface, ground and
grey waters) per unit of product for meat pro-
duction was greatest for grazing, then the mixed
crop-animal system and least for the industrial
systems. However, for dairy products the mixed
system had the lowest (20% lower) water foot-
print compared with grazing or industrial dairy
systems having quite similar, but larger foot-
prints. The primary reason for greater water
footprint from grazing, to mixed, to industrial
systems for meat production is the poorer feed
conversion efficiencies in systems where feeds
contain much more structural, fibrous carbohy-
drate (e.g. cellulose, hemicellulose and lignin) and
less non-structural carbohydrate (e.g. starch).
In their models, three to four times more feed dry
matter was required per unit of product princi-
pally due to difference in the utilization of the
carbohydrate fraction of the diet and conse-
quent poorer animal performance (Mekonnen
and Hoekstra, 2012).
Within dairy products (milk, butter and
cheese), the mixed crop-animal system resulted
in the smallest water footprint compared with
the grazing or industrial systems. This resulted
from greater feed conversion efficiency of dairy
animals consuming a mixed ration of forages
and concentrates combined with less water
requirement to grow the proper mixture of feeds
(Mekonnen and Hoekstra, 2012).
Overall, more feed required for greater ani-
mal productivity requires more water to produce
the feed, increasing the water footprint to pro-
duce the animal products. Of the total global
water footprint to produce crops, about 20% is
specifically for feed crops for livestock. In other
terms, it is estimated that about 12% of the total
global consumption of surface and ground-
water for irrigation is utilized to produce feed for
livestock, but not for food, fibres or other crop
products for direct human use. Additionally,
more water is required to produce concentrate
feeds (high in non-structural carbohydrates)
than roughage feeds (high in structural carbo-
hydrates or fibre). In the case of industrial beef
production (e.g. feedlots with high concentrate
feeding), the greater footprint comes predomi-
nantly from the large amount of water (e.g. via
irrigation) to grow the high-concentrate feeds
for finishing cattle rations. Also, Mekonnen and
Hoekstra (2012) noted that the industrial sys-
tem added extra excretory nutrients and required
more ground- and surface-waters for dilution
to meet nutrient load standards compared
with animal products from mixed-crop-animal,
or grazing systems where the nutrients could
be recycled directly to the soil. They specu-
lated that as per capita global wealth and
demand of meat consumption continues to rise
in coming decades (Steinfeld et al ., 2006), the
continuing intensification of animal production
will progressively exacerbate use of the world's
dwindling freshwater supply (Mekonnen and
Hoekstra, 2012).
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