The seasonality of reproduction is an
adaptive physiological process utilized by
wild animals to deal with seasonal changes
in temperature and food availability.
Domestication has led to an almost
complete loss of this adaptation in cattle
and pigs but it is retained in most breeds of
sheep, goats, horses and yaks originating
from temperate latitudes (Wuliji et al.,
2003). At these latitudes, photoperiod is
the main environmental factor that
determines the onset and duration of
breeding seasons. The timing of the
breeding season depends on the length of
the gestation period so that parturition
occurs in the spring. Thus, sheep and goats
(5 month gestation period) are short-day
breeders with conception occurring in
autumn and winter, whereas horses (11
months gestation period) breed during the
long days of spring (Ortavant et al., 1985).
Photoperiodic information is integrated
through a complex pathway involving
both neural and humoral steps.
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