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
2.1. Study design Ž
. The reproductive behaviour of 80 gilts PIC Camborough 15 and 14 large white
boars was recorded in detail over a 54-day period. The investigation was carried out in a
commercial farm where a dynamic service system was applied for all gilts. This consisted of 25 service pens, each with 4–5 boars plus 20 gilts. Each week, the four
oldest gilts were removed from each pen and replaced by four new gilts that had been Ž
. synchronised to come into oestrus 6–8 days after their entry see Section 2.3 . The gilts
were raised separately from the boars from weaning, thus, they had not had contact with the boars before they entered the service pens.
Altogether, the study lasted 54 days. Initially, the observations were carried out over 3-day periods at weekly intervals: from the 14th to the 17th of May, from the 21st to the
24th of May, from the 28th to the 31st of May and from the 4th to the 7th of June. Subsequent recordings were continuous from the 12th of June to 24th of July. All
recordings were started at 0900 h and covered the whole 24-h period.
2.2. Boars Ž
. Three teams of boars were used in the study 14 boars , with age varying from 325 to
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480 days. Two teams were used sequentially in pen A 16 and 11 months old and one Ž
. Ž
in pen B 14 months old . The oldest team of boars, in pen A, was replaced 29 days of .
which 12 were recorded after the beginning of the observations. The weight and hierarchy of the boars were determined in the middle of the study for the team in pen B
and the newly introduced second team in pen A, and for the old team of boars in pen A prior to their exit from the study. The hierarchy of the animals was determined by using
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pair feeding tests Meese and Ewbank, 1973; Craig, 1986; Brouns and Edwards, 1994 . All the boars in a group were raised as a team from weaning.
2.3. Dynamic system design Before their entry into the service pens, gilts were selected for conformation, teat
number and weight and were introduced into the gilt pools, with a dynamic population of 33 animals, at about 175 days of age and at least 105 kg liveweight. Prior to entry,
they were given an identification tattoo and injected with exogenous gonadotrophin Ž
. PG600, Intervet to induce pubertal oestrus. After 15–17 days in the gilt pools, the
animals were moved to the service pens, to mate them at their second oestrus. Every Friday at about 1230 h, four new gilts were introduced into each of the service
Ž pens, which contained four boars and sixteen gilts introduced over the previous 4
. weeks . The newly introduced females were moved to the service pens on a date basis,
without prior oestrus check, the objective of the system being to abolish the need for such labour-demanding procedures. In the present study, 10 new batches of four gilts,
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distributed into each of two service pens 80 animals in total , were observed over the 10-week study period.
The mating pens were 18 m = 10 m and constructed from metallic bars. Half the pen was deep straw and the other half was a dunging and feeding area. The dunging area of
the pen was cleaned daily prior to feeding. All the animals were floor-fed with 2–2.5 kgranimalrday of a standard commercial diet once per day at about 0900 h. Gilts were
kept in the service pens for approximately 33 days, after which they were removed from the pens and pregnancy diagnosed using ultrasonic scanning.
2.4. Lesion score recording and marking The level of fighting in the pens was measured indirectly by recording the skin lesion
Ž scores of the gilts. Lesion scores were recorded twice per week, on day 0 prior to entry
. into the service pen and days 3, 7, 10, 14, 17, 21, 24, 28 and 31 after entry. The gilt’s
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body was divided into sectors for scoring according to Luescher et al. 1990 . In an attempt not to confuse the lesions caused by the boars during mating events with the
lesions resulted from fighting between the gilts, the lesions at the upper part of the shoulders and the flanks were not included in the score. Lesions were scored according
to their length: lesions less than 2 cm were given one point, those between 2 and 4 cm were given two points and lesions bigger than 4 cm were given three points.
All the boars and gilts were marked twice per week using commercial spray markers of different colours. The gilts of the same batch were marked with the same colour but
were given a different symbol. 2.5. Recording equipment
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Four Panasonic Colour CCTV cameras two in each pen , one Panasonic TL700 Time Lapse Video Recorder, a Sanyo VQC-800 Colour Quad Compressor and a
Samsung Colour Television were used to record the sexual behaviour of the animals. Ž
. Thirty days were recorded in 72-h mode time lapse recording at 0.5-s intervals and the
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remaining 24 days in 96-h mode time lapse recording at 0.66-s intervals . 2.6. Mating quality recordings
In the current study, it was impossible to observe reliably by video whether Ž
. insemination with ejaculation by the boar took place in the observed sexual activities.
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For this reason, they are referred to as ‘mating attempts’ MAs or ‘mating events’ Ž
. Tanida et al., 1989 . A MA was defined as the continuous sequence of courtship
behaviour and mountings that began when one sexual partner started showing interest in Ž
the other e.g., turning hisrher head to hisrher sexual partner and started smelling and .
Ž nudging , and terminated when the sexual partners lost interest in each other e.g., boar
or gilt turned hisrher head in another direction than hisrher sexual partner and walked .
away , or when a competitor boar achieved his first successful mount after displacing the initial boar.
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For all the mating events n s 933 , the pen number, boar identity, gilt identity,
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number of attempted mounts AM , number of successful mounts, i.e., when boar spent Ž
. at least 10 s on the gilt’s back SM and the total time that the boar spent on the gilt’s
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back TTGB were recorded. For 606 of the observed mating events, all MAs recorded Ž
over a 30-day period within the study, additional recordings were made detailed
. Ž
recordings , including the time that precopulatory behaviour started i.e., an animal .
turning hisrher head to hisrher sexual partner and starting to smell or nudge them , the Ž
. Ž time to first mount TTFM
i.e., the time that elapsed from the start of the MA till the .
Ž boar exhibited the first mount , the time that the MA ended i.e., walking away by one
. of the sexual partners or successful interruption by another animal , the movement of the
gilt when the boar was on her back, and the reason for termination of the MA. The last Ž
. two parameters movement of the gilt and reason for termination were defined by using
the last boar mount within the MA sequence. This was because sexual behaviour in pigs consists of several mountings performed by the male and the way that the female
responds to these. In this study, gilts had not had boar contact before their entry into the service pens and responded rather fearfully to the first boar mounting attempts. Extent of
gilt movement while mounted was classified into four categories: a lot of movement Ž
. Ž
. 12 m, or the length of the service pen , some movement 1 but - 12 m ,
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immobile during the majority of the time mounted but some movement - 12 m just Ž
. before the boar dismounted, or rock solid immobile throughout . Additionally, it was
noted if the gilt, whilst not walking during the mount, moved by lying down whilst mounted. The reason for the termination of the observed MA was classified into five
categories: boar dismounted, gilt moved away, both partners separated simultaneously, interruption by another boar, interruption by another gilt or lying down by the mounted
gilt.
The overall quality of the observed MA was scored according to the following Ž .
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quantitative behavioural criteria: 1 the total time min that boar spent on the gilt’s Ž
. Ž .
Ž .
Ž . back
TTGB , 2
the mounting efficiency SMrAM = 100 , and
3 the ratio
TTGBrSM. According to these criteria, the observed MA were classified as illustrated in Table 1. These mating classes are partly based on earlier work by Hemsworth et al.
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1982 , Rikard-Bell et al. 1993 and Grigoriadis 1997 . When one mating event did not have all the qualifications to be placed in a qualified grade, it was ‘relegated’ to the next
lower grade, e.g., when in one mating the TTGB was 5 min and TTGBrSM was 3 Ž .
min but the ratio SMrAM was less than 75 then that mating was rated as ‘good’ instead of ‘ very good’.
In the dynamic service system, no independent check of oestrous state of the gilts is made since they are housed continuously with boars. To determine whether MAs were
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being made at appropriate i.e., during oestrus or inappropriate times, the individual records for each gilt were examined to determine the pattern of MAs received over time
and the gilt response in each case. MAs occuring in consecutive days over a period of up to 72 h, which incorporated a standing response by the gilt, were deemed to relate to the
occurrence of oestrus, and the onset of oestrus was defined as the time of the first such MA. MAs not conforming to these criteria were deemed to be inappropriately directed to
non-oestrous animals.
Table 1 Definition of the quality grades of MAs in the study
Very poor Poor
Fair Good
Very good Ž
. Ž
. Ž
. Ž
. Ž
. score 0
score 1 score 2
score 3 score 4
a
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TTGB min -
1.00 1.00–2.00
2.00–3.00 3.00–5.00
5.00
b
Ž . SMrAM
- 50
50–75 50–75
75 75
TTGBrSM -
1.00 -
1.00 1.00–3.00
1.00–3.00 3.00
a
Total time that boar spent on the gilt back.
b
Mounting efficiency s no. of successful mountsrno attempted mounts=100.
2.7. Statistical analysis The relationships between TTFM and TTGB and between TTFM and duration of
MA, also the number of MA and mating quality per hour of oestrus were analysed using
Fig. 1. The distribution of mating quality grades, gilt movement during service and reasons for MA termination of the 933 MAs recorded.
Pearsons’ correlation. Differences in nominal variables, for example, the mating quality score, were analysed using the x
2
-test. Where differences between different boar teams were demonstrated, data were also analysed for each team separately. Differences
between animals in ordinal data, for example, TTFM and MA duration of boars, were analysed using ANOVA incorporating effect of group and animal nested within group.
Differences in the mating frequency, MA duration and TTFM between boars of different social status were analysed using two-way ANOVA with social status and boar team as
factors. Post-hoc comparisons between pregnant and nonpregnant gilts were carried out using Student’s t-test. All the statistical analyses were carried out using the Minitab
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software package Minitab, 1998 .
3. Results
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