Genetics and Animal Welfare - Genetics and the Behavior of Domestic Animals - page 433

particular interest, fast-growing pigs display patterns of genetically deter-
mined pathologic alterations similar to those observed for human populations
afflicted by obesity ( Cummings and Schwartz, 2003 ).
With the exception of a short section on biotechnology at the end of this
chapter, all welfare problems discussed here were created with conventional
breeding methods. The animals are not GMOs (genetically modified organ-
isms) or products of biotechnology.

WELFARE PROBLEMS CAUSED BY HARMFUL
SOCIAL BEHAVIORS
Since the year 2000, harmful social behavior has been thoroughly researched.
In hens, selection for production traits such as greater egg production is asso-
ciated with increased feather pecking (Muir, Chapter 9). In pigs, selection
for production traits is associated with an increase in pig aggression, tail bit-
ing, and savaging of piglets (reviewed by Turner, 2011 ). Much of the current
research has been motivated by legislation in Europe to move away from
practices such as beak trimming or tail docking. The ban on gestation stalls
in Europe, and pressure from retailers in the United States to move to group
housing provides further impetus to develop less aggressive animals that still
have high levels of productivity.

Aggression in Sows
Practical experience shows that certain genetic lines of sows produce effi-
ciently in stalls but have high levels of fighting injuries when housed in
groups. Pig production companies that have successfully moved from gesta-
tion stalls to group housing have done so by changing genetics and selecting
for less aggressive sows. When sows were kept in individual stalls, there was
no informal selection by producers to eliminate the most aggressive animals.
Research clearly shows that aggression in sows is heritable ( d'Eath et al.,
2009a ). Chapter 11 of this topic, by Lotta Rydhmer, covers the genetic fac-
tors that affect sow aggression. Aggression interacts with other behavioral
traits in odd ways. Purebred Yorkshires and Yorkshire Landrace pigs that

stood still on a scale during weighing were less aggressive, and took longer
to move in and out of the scale (d'Eaath et al., 2009b). Fortunately, selecting
for less aggressive sows does not affect maternal ability ( Lovendahl et al.,
2006 ). On-farm observations indicate that pigs bred for lower aggression
must never be mixed with more aggressive pigs. Low-aggression pigs suffer
many attacks and may become severely injured.

3

Tail Biting in Pigs
Breuer et al. (2004) found that tail biting was heritable in Landrace pigs and
not in Large Whites. Breuer et al. (2004) found that genetic selection for