Reproductive and Maternal Behavior of Livestock - Genetics and the Behavior of Domestic Animals - page 177

period of estrus (5 7 days), variable estrus manifestation during seasonal

transitions, a fertile estrus in the early post-partum period (“foal heat”) and,
not uncommonly, display of estrous signs during pregnancy ( Crowell-Davis,
2007 ). The stallion has a vascular-muscular type penis and, under wild con-
ditions, is associated with his “harem” year-round ( McDonnel, 2000 ).
Horses are seasonal breeders with increasing daylight hours being the
trigger for increased ovulatory activity ( Palmer and Guillaume, 1992 ).
However, although feral horses may breed between May and October in the
Northern Hemisphere, domesticated horses have been selected to breed as
early as possible such that it is not uncommon for mares to cycle during
winter ( Aurich, 2011 ).
In the wild, horses form patriarchal family groups, usually containing a
stallion plus adult mares (the “harem”) and their young offspring, which are
maintained year-round and are non-territorial. The dominant stallion protects
the group while maintaining a strong social bond and discouraging interne-
cine disputes among the mares. This organizational structure enhances estrus
detection as well as reproductive success. Once individuals of either sex
reach sexual maturity, they are actively encouraged to leave their natal band,
probably to minimize the risk of inbreeding ( Heitor et al., 2006 ). Here, dis-
tinction is made between horses and some other members of the equid fam-
ily, such as donkeys, wild asses, and certain Zebras, which are territorial
breeders ( McDonnell, 2000 ) and exhibit behaviors typical of this category
such as the formation of sexually active groups of females and a relative
lack of herding behavior by the male ( Henry et al., 1991 ).
Colts will often exhibit mounting behavior towards their mothers or other
horses in the group during their first weeks of life, and sexual behavior may
be observed in 2

3-month-old colts ( Tyler, 1972 ). Young fillies will also
show similar behavior although to a lesser degree. The age at puberty in fil-
lies varies between 12 and 18 months, varying with the season of birth, and
mares will continue cycling until old age.

Male Reproductive Behavior
The social status of the mature stallion with respect to his ability to gain
access to a harem or not has important implications for reproductive physiol-
ogy and behavior ( McDonnell 2000 ), with these being significantly lower in
non-breeding “bachelor” groups. Here it is possible that the management
practices on multi-stallion breeding farms in which stallions are grouped
away from mares for extended periods may suppress reproductive capabili-
ties ( McDonnell, 2000 ).
Breeding stallions can show herding or driving behavior of mares, as
well as prancing behavior ( Houpt, 1998 ). When a stallion attends an estrous
mare, he “nickers” while smelling her external genitalia and groin. This is
usually followed by flehmen behavior as the penis becomes erect; a state