Genetic Influences on the Behavior of Chickens Associated with Welfare and Productivity - Genetics and the Behavior of Domestic Animals - page 334

line in a high-stress environment was more susceptible to viral infections.
Thus direct selection for low or high immune response would compromise
the birds' welfare as measured by longevity. Also, correlated responses on
productivity cannot be ignored. Birds with a high genetic potential for immu-
norespossiveness must divert energy from growth and reproduction to the
immune system.
SELECTION INVOLVING PRODUCTION TRAITS
Antagonisms
There is a natural antagonism between some undesirable behaviors and egg
production. Research has shown that selection to improve productivity based
on individual bird productivity was associated with increased aggressiveness
( Bhagwat and Craig, 1977, 1978; Craig et al., 1975; James and Foenander,
1961; Lowry and Abplanalp, 1972 ; Lee and Craig, 1981a; Tindel and Craig,
1959 ). From the reverse perspective, Craig (1994) has shown that selection
for social dominance will reduce performance when hens are housed in a
large group, but when housed singly, performance is increased. Bhagwat and
Craig (1978) found that social dominance increased in response to selection
for egg mass. Alternatively, direct selection for social dominance has been
shown to reduce performance when hens are housed in groups ( Craig, 1994 ).
Craig et al., 1965 and Craig and Toth (1969) showed that hens of White
Leghorn lines selected for high social dominance had lower rates of egg pro-
duction and higher mortality than did hens of the same line selected for low
social dominance. In addition, Craig (1970) showed that the high-social-
dominance line withstood crowing less well than the low-social-dominance
line. However, in single bird cages egg production of the high line was
superior to that of the low. Biswas and Craig (1970) also showed that the
high-strain hens had much lower production than the low line in floor pens
or multiple-bird cages, but were equally productive in single-bird cage. Craig
et al. (1975) demonstrated that stocks selected for part record egg produc-
tion, based on individual performance, exhibited more social dominance and
aggressiveness.
Other associations that are relevant include the finding that a stock
selected for increased productivity had greater feather loss than its unselected
control when kept in three-bird cages ( Lee and Craig, 1981b ). Also,
Choudary et al. (1972) compared four commercial lines of poultry and found
that the line which had the highest day rate of lay had the lowest hen-housed
rate of lay due to high mortality. Results from Lowry and Abplanalp (1970,
1972) showed that strains selected under floor-flock conditions became
socially dominant to both those selected in single-bird cages and unselected
controls. Craig and Lee (1989) detected a strong genotype by beak-treatment
interaction for egg mass per hen housed among three commercial lines. The