Genetics and Animal Welfare - Genetics and the Behavior of Domestic Animals - page 443

NERVOUS SYSTEM ABNORMALITIES DUE TO MUTATIONS
OR SELECTIVE BREEDING
The literature is full of examples of neurological or behavioral abnormalities
in dogs, pigeons, mice, rabbits, and rats. In most cases, the abnormalities
occurred as spontaneous mutations in laboratory stocks, which were then
continuously selected for research purposes. An example of spontaneous
mutation is muscular hypertrophy in Dorset sheep ( Cockett et al., 1996 ).
One of the most well-researched examples is nervous pointer-breed dogs.
Pointers are dogs selected to freeze and point when they see game birds hid-
den in the bushes. Pointing behavior is similar to an orienting response that
becomes frozen. The selection of pointers for the pointing trait may be selec-
tion for an abnormal orienting response. Breeders have known for years that
some dogs are so nervous that they are useless as hunting dogs ( Dykman
et al., 1979 ) The pointing trait and nervousness may be linked. A neurologi-
cally normal dog will orient toward a bird or other prey, then either chase it
or return to its original activity. A normal dog does not stay frozen in an
orienting posture. Breeders of pointers have recognized that a fine line exists
that divides a good pointer from a bad one. Dogs with a heightened pointing
response are generally too nervous to make reliable hunting dogs. Dykman
et al. (1979) and Peters et al. (1967) found obvious differences in the behav-
ior of normal pointers versus nervous pointers. Furthermore, visitors to the
laboratory could easily differentiate which dogs were from the nervous
genetic line. Nervous pointers cowered in their cages and failed to approach
visitors, whereas the normal pointers approached and wagged their tails.
Geneticists have selectively bred both normal pointers, with the charac-
teristic pointing behavior, and abnormal, nervous pointers. Nervous pointers
are excessively timid and display a hyperstartle response, avoidance of
people, and catatonic freezing in the close presence of people ( Klien et al.,
1988 ). Some nervous pointers display strikingly bizarre behavior. One dog
became “frozen” in a point and fell over when accidently bumped by another
dog ( McBryde and Murphee, 1974 ). It appears that with nervous pointers,
a continuum of neurological defects exists. Further research by Klien et al.
(1988) revealed that many nervous pointers were also deaf. Inherited deaf-
ness in lines of pointers selected for excessive nervous behavior is an autoso-
mal recessive trait, and the nervous trait may be inherited dominantly
( Steinberg et al., 1994 ).
The welfare of normal pointers (ones without the nervous trait) is accept-
able. However, nervous pointers may have very poor welfare unless raised
under specialized conditions. For example: training and environmental modi-
fication can help nervous pointers act more like normal dogs. McBryde and
Murphee (1974) found that training nervous pointers alongside normal poin-
ters made them less timid. The dogs from the nervous genetic line become
less timid and followed a normal pointer. After a period of training, the