Agriculture Reference
In-Depth Information
Table 5.1. Typical broiler performance in the USA (Gordon, 1974 a ; Havenstein et al ., 2003 b ).
Weeks of age
when sold
Live weight
(kg)
Feed efficiency (kg
feed per kg gain)
Year
Mortality (%)
1923 a
16.0
1.00
4.7
18.0
1933 a
14.0
1.23
4.4
14.0
1943 a
12.0
1.36
4.0
10.0
1953 a
10.5
1.45
3.0
7.3
1963 a
9.5
1.59
2.4
5.7
1973 a
8.5
1.77
2.0
2.7
1957 b
12.0
1.43
3.84
4.7
2000 b
6.0
2.67
1.63
3.6
Fig. 5.1. Contemporary comparison of (a) 1957 control and (b) 2001 selected broiler carcasses
slaughtered at different ages (from left; 43, 57, 71 and 85 days.). Photo by G.A. Havenstein. Permission
for use of Fig. 5.1 granted from the Annual Review of Ecology Evolution and Systematics, Volume 41,
1-19. ©2010 by Annual Reviews www.annualreviews.org.
Table 5.2. Proportional changes (%) in greenhouse gas (GHG) emissions and global
warming potential (GWP 100 ) per unit of animal product achieved as a result of 20 years
(1988-2007) of genetic improvement as calculated by Department for Environment,
Food and Rural Affairs (Jones et al ., 2008).
CH 4
NH 3
N 2 O
GWP 100
Chickens - layers
−30
−36
−29
−25
Chickens - broilers
−20
10
−23
−23
Pigs
−17
−18
−14
−15
Cattle - dairy
−25
−17
−30
−16
Cattle - beef
0
0
0
0
Sheep
−1
0
0
−1
has been observed in a long-term maize selec-
tion experiment, where oil content has con-
sistently increased 3% per generation for 100
generations (Dudley and Lambert, 2004). It
is likely that this sustained response is fuelled
by new mutations that arise each generation
(Hill and Kirkpatrick, 2010).
Since the early 1960s, livestock production
has grown rapidly with a worldwide fourfold
increase in the number of chickens, twofold
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