Agriculture Reference
In-Depth Information
environmental impact. First, they have an
increased milk solids concentration (480 g kg
−1
fat
and 370 g kg
−1
protein compared with 380 kg
milk fat kg
−1
and 310 g protein kg
−1
for the Holstein)
and thus a predicted Cheddar cheese yield of
125 g kg
−1
milk compared with 101 g kg
−1
milk
(Capper and Cady, 2012). Despite their reduced
milk yield (20.9 kg day
−1
compared with 29.1 kg day
−1
),
predicted daily cheese yield is therefore only
slightly less than the Holstein (2.61 versus 2.94 kg).
Second, mature US Jersey cattle have an average
bodyweight of 454 kg compared with 680 kg for
the Holstein, thus individual animals have a
smaller maintenance requirement. If equivalent
quantities of Cheddar cheese production were pro-
duced from Jersey and Holstein cow populations,
the assumption that dairy population size can be
used as a proxy for environmental impact does not
hold true. Although the interaction between milk
yield and milk solids concentration meant that the
Jersey population required to produce 500,000 Mt
of cheese yield contained 9% more animals than
the Holstein population, the body mass of the
Jersey population was reduced by 26% and the
population maintenance energy requirement
by 22%. Consequently, water use was reduced by
32%, land use by 12% and GHG emissions by 20%
per unit of cheese yield. Within this comparison,
the major factors affecting resource use and GHG
emissions were milk yield, milk solids content and
animal bodyweight, thus although productivity is
a key contributor, it is not the sole arbiter of live-
stock sustainability. The concept of reducing main-
tenance requirements is also being adopted within
both the beef and dairy industries through select-
ing animals with a low residual feed intake (RFI),
i.e. those animal that require less feed to support
maintenance and production than they would be
predicted to consume (Herd and Arthur, 2008;
Crozier and ZoBell, 2010). If future genetic indices
are developed to the extent that producers are able
to select effectively for low RFIs, this would be pre-
dicted to have a significant impact on environmen-
tal sustainability through improved efficiency.
with conventional livestock production. Demand
for organic and 'natural' foods is increasing in
developed countries where malnutrition is more
often associated with obesity than undernour-
ishment, and consumers have sufficient income
to demand greater food choice. In the USA,
organic food commands a small portion (3.7%)
of total market share (Organic Trade Association,
2010) with the greatest market shares being
seen in the fruit and vegetable (12%) compared
with dairy (6%) or beef (2.5%) sectors (Clause,
2010; Organic Trade Association, 2011). Recent
data show that almost 95% of US consumers
buy food according to economic, nutritional and
taste aspects, with only 4% seeking food accord-
ing to their specific lifestyle choices (e.g. vege-
tarian, organic or local), and yet a majority of
consumers will occasionally buy organic foods
(Simmons, 2011). A survey by Raab and Grobe
(2005) reported that consumers associated
organic foods with positive attributes including
'chemical-free', 'healthier/more nutritious',
'clean/pure' and 'earth-friendly'. It is clear that
the intensification of US livestock production
over the past century has considerably reduced
both resource use and GHG emissions per unit
of animal protein. None the less, a small yet
vocal proportion of the population advocate for
pasture-based or organic systems (Pollan, 2007;
Salatin, 2007; Gumpert, 2009), citing differ-
ences in the nutritional quality or environmen-
tal impact of animal proteins produced in
extensive systems.
Pelletier
et al
. (2010) reported that GHG
emissions per unit of beef were greater in pasture-
finished systems than in feedlot systems. This
result seems intuitively incorrect; a conventional
system that finishes animals on maize-based
diets grown with significant fertilizer inputs,
transports both feed and animals across the
country, and houses animals in confinement
appears to have intrinsically lower environmen-
tal sustainability than a grass-finishing system.
None the less, from a biological viewpoint, the
results are easy to explain. Growth rates are
considerably less in animals finished on grass
and it is difficult to achieve heavier slaughter
weights, therefore grass-finished cattle are usu-
ally slaughtered at around 486 kg at 679 days
of age, compared with 569 kg at 444 days of age
in a conventional system (Capper, 2012). As a
consequence of the reduced slaughter weight,
Environmental Sustainability
of Organic and Pasture-based
Systems
The social acceptability of organic or pasture-
based systems is generally improved compared
