1. Introduction
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Mating behaviour of individuals varies greatly in swine Gordon, 1997 and the nature of the mating behaviour can influence the production outcome in terms of
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conception rate and litter size Hemsworth et al., 1978; Rikard-Bell et al., 1993 . However, the origin and precise significance of this individual variation is largely
unstudied. At the present time, the majority of matings take place under very controlled conditions, but consumer demands related to animal welfare considerations are bringing
about a change to more extensive production systems in many countries.
Such an alternative system is the dynamic service system, which is a variant of group mating, and has recently been developed in outdoor production systems in Denmark
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Goss, 1996 . In a dynamic mating system, a team of boars is placed with a group of females and copulation takes place with minimal supervision. Moreover, the female
population of each group is changed on a regular, often weekly, basis. Such a system has its advantages and its disadvantages. The dynamic service system is generally consid-
ered as animal welfare friendly, since the animals are not confined and have greater opportunity to express normal behaviour; it demands low labour requirement and low
building investment, since it permits reduced space requirement per animal in compari- son with systems involving individual housing of boars and controlled mating. On the
other hand, there is an unavoidably high percentage of unseen and, therefore, unsuper- vised services, an elevated level of fighting, especially when the new females enter the
service pens, difficulty of checking individual boar fertility and mating efficiency, the risk of injury resulting from fighting between boars, which may leave a boar impotent
and the need for a big number of teams of boars.
To date, studies have focused on group mating systems with multiparous sows Ž
. Tanida et al., 1989, 1991; Shaw and Edwards, 1995; Rigat et al., 1998 . The behaviour
and reproductive performance of gilts in systems of this nature may differ from that of older sows. Gilts enter the system without experiencing lactation, thus they are less
variable in size and body condition and better suited to cope with group-housing where competition for resources can severely disadvantage animals with small size or low body
condition relative to other group members. Conversely, their smaller body size and lack of breeding experience may have detrimental effect on their reproductive behaviour in
uncontrolled conditions. Since, in a practical situation, gilts present greater difficulties in induction of predictable oestrus and management of mating than weaned sows, a
controlled dynamic service system has significant commercial potential. No analysis of such a system has yet been reported and the present study was designed to provide this
information.
2. Materials and methods
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