Reproductive and Maternal Behavior of Livestock - Genetics and the Behavior of Domestic Animals - page 174

nudgings, and emitting a series of soft, guttural grunts. Categories of boar
courtship and service behavior noted by Tanida et al. (1989) included sniff-
ing, head to head, nosing, following, chin resting, mounting, and copulation.
When the estrous female assumes the mating stance, more vigorous muzzling
of the genital region occurs accompanied by continuous grunts, teeth grind-
ing, foaming from the mouth and rhythmic urination. Experienced boars will
generally mount rapidly at this juncture, although some will mount and
dismount a number of times prior to copulation. Ejaculation is prolonged
(3

20 minutes) compared with other livestock species, with the female
remaining immobile throughout. The mating reaction of boars is stimulated
by both visual and tactile factors, and can easily be elicited by immobile
objects resembling the rear end of a female. Full erection of the fibroelastic
penis generally occurs once mounting is achieved ( Signoret et al., 1975 ).
Significant breed and strain differences in both swine libido and mating
behavior have been reported ( Chenoweth and Landaeta-Hern ´ ndez, 1998 )as
well as differences in the duration of ejaculation ( Signoret et al., 1975 ).
When comparing successful mating attempts in young boars, Yorkshires
were more successful than Durocs and crossbreds were generally superior to
purebreds ( Neely and Robison, 1983 ).
When boars were selected for 10 generations on the basis of testosterone
(T) response (high or low) to GnRH challenge, the heritability was moderate.
In addition, litter sizes in females of the high-T response line were signifi-
cantly larger than those in females of the low T-response line ( Robison
et al., 1994 ). Rothschild (1996) , quoting a number of studies on the heritabil-
ity of boar libido, provided a general estimate of 20% (range 10

50%).

Female Reproductive Behavior
Under open range conditions, pre-copulatory behavior can last for some
time, with the female becoming more restless and nervous several days
before estrus. During this phase she will resist the boar's advances although
staying in his proximity. When she reaches the stage of receptivity, she will
show more direct interest in the boar via nuzzling, head to head contact, and
occasional mounting attempts of the boar. When willing to mate, she adopts
the mating stance allowing the boar to mount and copulate. This stance is
characterized by rigidity, arching of the back, and cocking of the ears.
The presence of the boar facilitates estrus detection. For example, in one
study, only 45% of estrous gilts exhibited the standing reaction in the
absence of the male. However, 90% of these displayed the standing reaction
when the boar was proximate and the addition of visual and tactile stimuli
resulted in all responding.
Breed differences are evident in the age at which females attain puberty
( Hurnick, 1987 ). Rydhmer et al. (1994) reported heritability estimates for
estrous traits, such as length of proestrus and ability to show the standing