Agriculture Reference
In-Depth Information
40 years (Rischkowsky and Pilling, 2007),
further efficiency improvements may be nec-
essary within these industries to reduce
future environmental impact. Vertical inte-
gration and consolidation within both indus-
tries has considerably improved productivity
over the past 50 years. According to historical
USDA data, between 1963 and 2009, average
US swine carcass weight increased by 27 kg,
from 65 to 92 kg (USDA, 2012). This allowed
total carcass weight (slaughtered animals ×
average carcass weight) to increase from 5.4
to 10.5 billion kg (a 92% increase) while
slaughter numbers only increased by 44%
(35 million animals). Despite the increase in
slaughter numbers, the US swine breeding
population declined from approximately
9.1 million head to approximately 5.9 million
head, as a function of both increased litter
size and a greater number of farrowings per
year. In contrast to the beef system, where
multiple offspring (twins or triplets) are gen-
erally perceived to be undesirable, improved
reproductive performance in terms of
increased litter size is therefore a significant
factor in swine productivity. Indeed, Thoma
et al
. (2011) demonstrated a positive impact
of increased litter size on carbon emissions from
swine production, and Vergé
et al
. (2009) noted
reductions in GHG emission intensity resulting
from higher birth rates in the Canadian pork
industry between 1991 and 2001.
Average chicken slaughter weight also
increased from 1.61 to 2.54 kg between 1963
and 2009, facilitating a 594% increase in
chicken production (3.17 to 29.4 billion kg)
with only a 3.4-fold increase in slaughter num-
bers (1.96 to 8.66 billion head; USDA, 2012).
Poultry growth rates and feed efficiency also
improved considerably over the past 60 years,
reducing the time from hatching to slaughter
from 90 days to less than 40 days (Konarzewski
et al
., 2000). Evidence from feeding studies
involving heritage-style chicken breeds suggests
that although nutrition and management have
played a significant role, the majority of this
improvement has occurred through genetic gain
(Havenstein
et al
., 2003; Schmidt
et al
., 2009).
Although environmental analysis of gains made
in the US pork or poultry industry over time have
yet to be executed, results of the aforementioned
historical beef comparison suggest that the
increases in monogastric carcass weight and
growth rates, and reductions in supporting pop-
ulation sizes would be expected to have mitigated
the environmental impact per unit of pork or
poultry over time.
The Role of By-product Feeds in
Animal Agriculture and Livestock's
Competition for Human Food
A question is often posed as to whether livestock
systems can achieve further productivity gains
in future without significant genetic or techno-
logical intervention, both of which may be
unpalatable to the consumer. This is further
exacerbated by consumer concern over the use
of crops for animal feed that could instead be
used as human foodstuffs (Gill
et al
., 2009).
Given the feed efficacies and growth rates already
exhibited within monogastric production sys-
tems, there may be less opportunity to improve
these metrics than in ruminant livestock. How-
ever, monogastric diets are primarily based on
maize and soybean, thus the use of by-products
from the human feed and fibre industries, which
have a considerably smaller carbon footprint
(as the majority of carbon emissions can be
attributed to food or fibre), may be a potential
avenue to further mitigate GHG emissions from
monogastric animal production. Ruminant sys-
tems provide for the conversion of human-
indigestible plant material (forages, pastureland
and by-product feeds) into high-quality animal
protein for human consumption. The majority
of land used for grazing ruminants is not suita-
ble for growing crops for human consumption,
indeed data from the USDA's Economic Research
Service (Lubowski
et al
., 2006) indicate that only
8% of US grazed land is sufficiently productive to
be classified as cropland pasture, therefore using
pastureland to support, for example, the cow-
calf sector of beef production provides an oppor-
tunity to feed the human population without
competing for grain-based food resources. This
is discussed at length by Wilkinson (2011), who
redefined conventional measures of feed effici-
ency (e.g. 7.8 kg feed per kg of gain for feedlot-
finished beef compared with 3.6 kg feed per kg
of gain for pork) to account for human-edible
energy or protein feed inputs compared with the
