Genetic Influences on the Behavior of Chickens Associated with Welfare and Productivity - Genetics and the Behavior of Domestic Animals - page 324

inferior in ability to win pair contests when matched with non-inbreds, and
pullets' peck-order status was negatively associated with their inbreeding
coefficients.
McGibbon (1976) observed that the incidence of floor laying in pens
increased as inbreeding increased in lines originating from random-bred
populations of White Leghorns (Cornell Control) and Rhode Island Reds
(Regional Reds). This evidence suggests that homozygous recessive genes
were involved. However, environmental conditions during the rearing period
were also identified as being influential; floor laying was more prevalent
among confinement-reared pullets than in range-reared pullets.
Differentiation associated with keeping relatively small subpopulations
isolated over several generations was illustrated for fear-related escape and
avoidance behavior by Craig et al. (1983) . One of two subpopulations
selected alike required about 10-times as long to recover from fear as did the
other ( Craig et al., 1983 ). Likewise, differences in “righting time” following
the induction of tonic immobility were present within some pairs of similarly
selected lines ( Craig et al., 1984 ).

MENDELIAN TRAITS
Genes having major effects on morphology and the nervous system are
typically deleterious in terms of the well-being of affected individuals and
often affect their behavior ( Axelsson and Ellegren, 2009; Eyre-Walker and
Keightley, 2009; Siegel and Dunnington, 1990 ). Such genes are usually
either sex-linked recessives, which may be expressed in non-inbred stocks,
or autosomal recessives, most likely to be seen following inbreeding.
Because of the generally deleterious effects of these major genes they are
selected against and are not seen in commercial stocks except at very low
frequency for homozygous recessive phenotypes.
Some major genes, seemingly having adverse effects, may not be as
disadvantageous as they seem at first consideration. For example, results of a
study carried out by Ali and Cheng (1985) are relevant. They compared
genetically blind hens (rc/rc) and sighted hens (Rc/rc) segregating from mat-
ings of Rc/rc rc/rc chickens. During a 2-month experimental period, blind

hens were less active, had better feather cover, produced more eggs, required
less feed, and did not differ in body weight from sighted hens.

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SELECTION INVOLVING BEHAVIORAL TRAITS
Behaviors associated with welfare and productivity in commercial stocks are
typically under polygenic control and are measured in quantitative terms.
However, some, such as “broody” behavior, are more of an all-or-none
nature. Both autosomal and sex-linked genes may be involved. Because
selection studies are costly and time consuming, breeders often depend on