Biology Reference
In-Depth Information
which must be fully achieved before intromission can occur. Erection is rela-
tively slow due to the vascular
muscular mechanisms involved, and copula-
tion depends upon successful foreplay which is of greater importance in
horses than in most livestock species ( Houpt, 1998 ). Visual and sensory sti-
muli are essential for successful foreplay by the stallion, with an important
aspect being the posture of the mare in concert with other signs of receptivity
as discussed below. However, in common with other livestock species, males
can be trained to accept a surrogate, for example a dummy, which has some
similarities to the rear end of an immobile mare. Here, experienced stallions
will not show inhibitions in mounting an appropriate dummy, although inex-
perienced males often require application with urine from an estrous female
before they will attempt to mount ( Houpt, 1998 ).
Experienced stallions will mount readily with an average of 1.4 mounts
(range 1
4) per copulation. Ejaculation, accompanied by rhythmical con-
tractions of urethral muscle and characteristic flagging tail movements occur
an average 13 seconds after intromission. Stallions may breed several times
in a day with satiation being achieved on average after 2.9 ejaculations
(range 1
10) in succession ( Bielanski and Wierzboweski, 1961 ). Young stal-
lions can be very aggressive in approaching an estrous mare and may show
inexperience in mounting. Masturbation is common in confined stallions,
although rarely accompanied by ejaculation ( Houpt, 1998 ). Stallions show
peak sexual behavior in spring, with this being lowest in winter and highest
in spring
summer ( Pickett et al., 1975 ).
Female Reproductive Behavior
Under natural conditions, mares play the major role in the mating process
through their proceptive behaviors by stimulating the stallion and timing
copulation ( McDonnell, 2000 ), with older mares being more proactive than
younger ones ( Heitor et al., 2006 ). Proceptive females will approach and
actively solicit the stallion. Once receptive, they will present their hindquar-
ters to the stallion and lower the pelvis while deviating the tail and exhibit-
ing clitoral “winking”, often while voiding small amounts of urine. Under
conditions in the wild, this will usually involve the “harem” male, for which
the mare has established strong social bonds. Under domesticated conditions,
the mare and stallion are often not familiar ( Crowell-Davis, 2007 ), and mares
can show preferences for, and dislikes of, particular stallions to the extent
that estrus signs may be modified accordingly. Sexual attraction of mares to
a particular stallion is influenced by coat color, age, dominance rank, and
days from ovulation ( Heitor et al., 2006 ; McDonnell, 2000 ).
Hand-breeding of horses, where the mare and stallion are brought together
at the time of breeding only, is often preceded by the process of “teasing”
whereby a mare is exposed to a stallion which can interact with her without
fear of injury to either animal. The behavioral responses which the stallion
Search WWH ::




Custom Search