Agriculture Reference
In-Depth Information
5
Genetics and Sustainable Animal
Agriculture
A.L. Van Eenennaam*
Department of Animal Science, University of California,
Davis, California, USA
Introduction
slaughter weight of 0.4 kg as is dramatically
illustrated in Fig. 5.1. Concurrently, the feed
conversion ratio (kg feed per kg gain) was
reduced by 15%. These remarkable improve-
ments in production efficiency have resulted in
dramatic reductions of the inputs required to
produce a kilogram of chicken. However, it has
been argued that this was achieved without
adequately considering important social and
animal welfare components of sustainability.
From an environmental perspective, genetic
improvement over the past 50 years has also
resulted in reductions in greenhouse gas (GHG)
emissions and global warming potential per unit
of animal product (Table 5.2). Capper
et al
.
(2009) reported that although the carbon foot-
print per individual cow increased when com-
paring 1944 with 2007, due to increases in the
milk production per cow, the carbon footprint
per unit of milk in 2007 was 63% lower than in
1944. It has been observed that despite intense
selection on specific traits (e.g. 8-week body
weight in broiler, milk yield in dairy cattle) the
selection response per generation for these
traits shows no sign of decreasing. Mean milk
yield in the USA has more than doubled during
the 50 years starting in 1957 from 5,859 to
12,043 kg year
−1
per cow, with a rate of 1%
yield increase per generation. A similar trend
Genetics may not be immediately associated
with the term sustainability, and yet the impor-
tance of animal genetics in contributing to the
interplay between the environmental, social and
economic goals of sustainability should not be
underrated. Genetic gains are both permanent
and cumulative meaning that gains made in
1 year will be transmitted to subsequent genera-
tions without further endeavour or expenditure.
Genetic improvement has been an important
component of the tremendous advances in agri-
cultural productivity that have occurred over
the past 50 years. Perhaps this is nowhere more
evident than in poultry breeding (Table 5.1).
The body weight of broiler (meat) chickens at
8 weeks of age has increased from 0.81 to
3.14 kg between 1957 and 2001, and approxi-
mately 80% of this fourfold increase was due
to genetic selection (Havenstein
et al
., 2003).
Increased productivity clearly benefits the eco-
nomics of production. Animals that can be
grown to market weight at a younger age use
proportionally less of their total feed intake on
maintenance energy. In 1960, the average time
needed to produce a broiler chicken in the USA
was 72 days. By 1995, this was reduced to
48
days, including an increase in average
