Agriculture Reference
In-Depth Information
with the year that each trait was introduced. It
can be seen that production traits (milk and fat)
were the first traits incorporated into selection
programmes. As time went on, more functional
traits were included to widen the scope and redi-
rect the emphasis of breeding programmes. At
the current time, production traits represent
35% emphasis within the BO, with the remain-
ing 65% placed on functional traits (Cole et al .,
2009). The genetic correlation between body
weight and incidence of leg disorders in broilers
is positive, so appropriate multi-trait selection
indexes have been developed to permit a genetic
improvement in leg health concurrently with
continued, though more modest, improvement
in growth rate. In recent years, genetic selection
has had a major impact on decreasing the inci-
dence of skeletal disorders in broiler chickens
(Thiruvenkadan et al ., 2011). Similarly, envi-
ronmental considerations can be included in BO
and index calculations (van Arendonk, 2011).
Some breeders have also incorporated
behavioural traits into their selection criteria.
It may be considered unethical to select for
behaviours that better suit an animal to an
agricultural production environment, with
some advocating that the production environ-
ment should be modified to suit the animal.
However, it should be recognized that livestock
populations have been selected for behav-
ioural traits since their domestication. While
altering the environment might be appropri-
ate in some cases, such a change needs to be
considered in the context of undesired nega-
tive impacts on other components of sustain-
ability. It is conceivable that selection to better
suit a population of animals to their produc-
tion environment could improve animal wel-
fare and productivity, thereby working
towards multiple sustainability goals.
An example from the poultry industry illus-
trates this point well. Muir (1996) performed a
selection experiment with a line of White
Leghorns to improve adaptability and well-being
of layers in large multiple-bird cages. Feather
and vent pecking, and sometimes cannibalism
can occur in multi-pen cages, a problem that can
be managed with beak trimming young birds.
Muir used a selection approach termed 'group
selection'. In this experiment, offspring from
select roosters were housed as a group in multi-
ple-bird cages, and the group was either selected
or rejected based on the productivity of the
group. An unselected control, with approxi-
mately the same number of breeders as the
selected line, was maintained for comparison
and housed in single-bird cages. After six gener-
ations, annual mortality of the selected line in
multiple-bird cages decreased from 68% to
8.8%. Mortality of the selected line in multiple-
bird cages was similar to that of the unselected
control in one-bird cages. Annual survival
improved from 169 to 348 days, eggs per hen
per day rose from 52% to 68%, total eggs per
hen from 91 to 237 eggs, and total egg mass
from 5.1 to 13.4 kg, while average egg weight
remained unchanged. The author concluded
that these data suggested group selection could
eliminate the need to beak-trim to avoid canni-
balism by breeding hens to better suit multiple-
bird cage production systems. These outcomes
from group selection would seem to align with
several sustainability goals, including decreased
cannibalism and a resultant improvement in
animal welfare, better production efficiency,
reduced need for beak trimming, and group
housing rather than single-bird cages. In reality
it is likely that moving to alternative production
systems (e.g. free range) will necessitate 'rese-
lecting' for animals that are better suited to the
new production environment. With too much
space, birds become territorial and it is not
uncommon to have much greater mortality in
floor pens than cages due to the increased area
(Muir and Cheng, 2004).
Other aspects of sustainability are not so
easily addressed using a selection index approach.
In an excellent review, the current status of valu-
ing animal welfare issues in breeding goals is dis-
cussed in Nielsen et al . (2011). The difficulty of
defining sustainable breeding goals is to value
intangibles in monetary terms. Assigning MV to
traits related to animal welfare continues to be a
challenge because it is both a 'public good' and
subject to 'market failure'. Public good is an eco-
nomic term meaning that the good is 'non-rival'
and 'non-excludable' in consumption. Non-rival
means that the consumption of the good by one
individual (e.g. improved chicken housing) does
not preclude another from consuming the same
good. Non-excludable means that no one can be
effectively excluded from using the good includ-
ing those that may not eat chicken. Market fail-
ure is an economic term that refers to a situation
Search WWH ::

Custom Search