Genetics and Animal Welfare - Genetics and the Behavior of Domestic Animals - page 432

production traits such as rapid growth, leanness, and high milk yield.
Unfortunately, some of these concerns have materialized. Many scientists are
worried about indiscriminate selection for production traits that seriously
compromise animal welfare. Presently, the dairy cow is producing more milk
than its ancestor would have produced. The amount is 10-times the beef
cattle average of 1000 2000 kg ( Webster, 1993 ). Due to this high metabolic

drain, many Holstein cows are only “productive” for two years and are
slaughtered around the age of four when profitability drops. Selection for
increased milk production has also led to epidemics of so-called “production-
related diseases,” such as lameness and mastitis, the two leading causes of
dairy cow mortality in the United States (USDA, 2008) .
The improvements in plant and animal production is largely a result
of genetic selection. Turner (2011) warns that selection for economically
important traits may be a factor in the expression of behaviors detrimental to
welfare. Some examples are aggression in pigs and feather pecking in laying
hens. The use of genomic information has the potential to help breeders select
against harmful behavior, but if it is used indiscriminately, it could accelerate
selection of harmful behaviors. Prunier et al. (2010) , Jensen et al. (2008) , and
Rodenburg and Turner (2012) all state that new breeding tools could be used
to improve animal welfare by selecting against harmful behaviors.
Several long-term selection studies using a variety of small mammals
have clearly shown that over-selection for a single trait may have adverse or
unexpected effects on other traits ( Belyaev, 1979; Dobzhansky, 1970;
Lerner, 1954; Wright, 1978 ). Belyaev (1979) and Belyaev and Borodin
(1982) demonstrated the effects of over-selection for a single trait in long-
term selection experiments in foxes. Selecting foxes for a single behavioral
trait (tameness) caused unexpected changes in coat color, breeding cycles,
hormonal profiles, and subsequent changes in body traits. One theory is that
the genes guiding the animals' behavior do so by altering chemicals in their
brains. Changes to those neurochemicals have “downstream” influences on
the animals' physical appearance (Kukekova, Chapter 10).
In domestic pigs, selection for meat production traits has resulted in
animals with lowered reproductive ability ( Dickerson, 1973 ). To compensate,
modern pork producers often use maternal sow lines selected for high repro-
duction ability, bred to sire lines selected for high meat production. The
resulting offspring are terminal cross pigs fattened for market. Buchanan
(1987) stated that the use of crossbreeding in the swine industry has
increased in the last 60 years. In the 1990s, most commercial market pigs
were crossbred. The use of hybrid sire and dam genetic lines is still a stan-
dard practice in 2012. Genetic selection of highly inbred lines with extremely
fast growth rates is associated with biochemical disorders. Some of the meta-
bolic diseases associated with genetic selection are Mulberry heart disease
( Shin et al., 2011 ), porcine stress syndrome ( Leman et al., 1992 ), and osteo-
chondrosis, a disease of bone and cartilage growth ( Stern et al., 1995 ). Of