Genetics and Animal Welfare - Genetics and the Behavior of Domestic Animals - page 436

egg production and increased appetite are related. Fisikowski et al.(2008) found
that two sub-haplotypes of the DRD4 gene are associated with feather pecking.
Dopamine genes are associated with exploratory behavior in many species. This
finding is additional evidence that foraging behavior and/or increased appetite
is related to high feather pecking. Behavioral observations also show that hens
perform gentle pecks during dust bathing and vigorous pecks when foraging.
Pecking behavior directed toward other birds resembles pecking behavior dur-
ing foraging ( Dixon et al., 2009 ). In a subsequent study, the same research team
showed that providing environmental enrichment opportunities for foraging are
effective for reducing feather pecking ( Dixon et al., 2010 ). Kjaer and Jorgensen
(2011) found that birds from a high-feather-pecking line had higher autonomic
nervous system arousal during physical restraint compared to those from a
low-feather-pecking line. Brunberg et al.(2011) suggest that feather pecking
may serve as a model for human obsessive

compulsive disorder. This study
provides a gene list that may be useful in further research on the mechanisms
behind feather pecking.

EFFECTS OF OVERSELECTION IN CATTLE AND PIGS
Since 1971, the first author has observed hundreds of thousands of animals
at slaughter plants, farms, and feedlots in the United States, Canada, Europe,
Australia, and New Zealand. In the early 1990s she began to observe an
increased number of highly excitable, nervous pigs and cattle. These animals
were more difficult to handle and more likely to panic and become extremely
agitated when subjected to sudden novel experiences. For example: a light
tap on the rear causes squealing in pigs with an excitable temperament, but a
tap on the rear has little effect on pigs with a calmer temperament. The
appearance of highly excitable and difficult-to-handle animals appeared to
coincide with genetic selection for both rapid growth and high, lean meat
yield ( Grandin, 1994 ). In cattle, the most reactive animals are primarily
crossbreeds from the European continent. In the United States, these cattle
became popular when producers started selecting for lean beef ( Grandin,
1994 ). Along with welfare problems and handler safety issues, highly
excitable animals have an increase of meat-quality problems. Cattle that
become highly agitated during handling are more likely to have tough meat
and more dark cutters ( Voisinet et al., 1997 ). Many studies now show an
association with poorer meat quality and excitable temperaments in cattle
( del Campo et al., 2010; Muchenje et al., 2009; Turner et al., 2011 ), and
pigs ( Barton-Gade, 1984; Sayre et al., 1964 ). Pigs that become excited just
before slaughter have more PSE and lower meat quality. Since the first edi-
tion of this topic, an industry-wide acceptance of this problem has motivated
producers to select intensively for calmer cattle (see Chapter 4 on cattle tem-
perament testing). The results are calmer, easier to handle cattle with better
meat quality ( Ribeiro et al., 2012 ). However, increased selection for calm