www.elsevier.comrlocaterapplanim
The reproductive behaviour of pigs in a dynamic
service system for gilts
Dimitris F. Grigoriadis
a,), Sandra A. Edwards
a,
Peter R. English
a, Forbes M. Davidson
b aDepartment of Agriculture, UniÕersity of Aberdeen, 581 King Street, Aberdeen, AB24 5UA, UK b
A. Simmers, Mains of Bogfechel, Whiterashes, Aberdeenshire AB2 0QU, UK
Accepted 26 August 1999
Abstract
The behaviour of 80 gilts and 14 boars was observed over a 54-day period in a dynamic service system with pens of 20 gilts and 4–5 boars. The female population of this system was
Ž .
changed on a regular basis four animals in four animals out per week while boars were resident.
Ž .
Altogether 933 mating attempts MAs were recorded and their quality was classified using quantitative behavioural criteria. Only 9% and 18% of the observed MAs were classified as ‘ very good’ and ‘good’, while 14, 24 and 35% were ‘fair’, ‘poor’ and ‘ very poor’, respectively.
Ž
Differences between and within boar teams in the mating quality parameters were significant all
. Ž .
p-0.05 . A significant correlation was found between time to first mount TTFM and MA
Ž .
duration rs q0.58, p-0.01 . MAs followed a diurnal pattern and had a peak at about 0900 h
Žafter feeding time . The number of MAs a gilt received per hour of oestrus decreased. Žrs y0.55, p-0.001 , while mating quality score improved. Žrs q0.38, p-0.005 . The.
overall pregnancy rate was 84%. Gilts with a positive PD result had received more total MAs and
Ž .
total ‘good’q‘ very good’ MAs Ts2.33, p-0.05 and Ts2.25, p-0.05, respectively , and
Ž .
were significantly heavier at the time of selection Ts2.80, p-0.01 . Mating quality grade
Ž 2 .
differed significantly with boar social status x s35.8, dfs16, p-0.01 but this had no
Ž .
influence on mating frequency, time to first mount or mating duration all p)0.05 , indicating that subordinate boars were not deprived of sexual partners. Gilt lesion scores reached a maximum
Ž .
3 days after entry then subsequently declined rs y0.75, p-0.05 . It was concluded that with a good knowledge of the factors influencing the activity of the sexual partners kept in such a system, the dynamic service system could be a valuable alternative in future pig production.
q2000 Elsevier Science B.V. All rights reserved.
Keywords: Pig; Sexual behaviour; Mating conditions; Dominance relationships; Agonistic behaviour
)Corresponding author. Tel.:q44-1224-274122; fax:q44-1224-273731; e-mail: agr881@abdn.ac.uk 0168-1591r00r$ - see front matterq2000 Elsevier Science B.V. All rights reserved.
Ž .
1. Introduction
Ž .
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
Ž .
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
ŽGoss, 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
ŽTanida 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 .
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
Ž .
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
Ž .
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
ŽPG600, 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,
Ž .
distributed into each of two service pens 80 animals in total , were observed over the 10-week study period.
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
Ž .
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
Ž .
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
Ž .
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.
Ž .
For this reason, they are referred to as ‘mating attempts’ MAs or ‘mating events’
ŽTanida 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.
Ž .
For all the mating events ns933 , the pen number, boar identity, gilt identity,
Ž .
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
Ž .
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
.
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)12 m, or the length of the service pen , some movement. Ž)1 but -12 m ,.
Ž .
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 . Ž .
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.
Ž1982 , Rikard-Bell et al. 1993 and Grigoriadis 1997 . When one mating event did not. Ž . Ž .
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
Ž .
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
Žscore 0. Žscore 1. Žscore 2. Žscore 3. Žscore 4. a
Ž .
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
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
Pearsons’ correlation. Differences in nominal variables, for example, the mating quality score, were analysed using the x2-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
Ž .
software package Minitab, 1998 .
3. Results
3.1. Mating quality aspects
Almost one third of the observed MA were classified as ‘ very poor’ and only 9%
Ž .
were rated as ‘ very good’ Fig. 1 . In more than 60% of the cases, the gilt was immobile
Ž .
during the final boar mounting or she exhibited only some movement -12 m . On the other hand, in 23% of the observed MA, the gilt appeared agitated at having the boar on her back and moved around the pen to avoid this. Also, from Fig. 1, it can be seen that 45% of the services were ended by gilts either moving away or lying down. In this latter case, the gilt suddenly appeared to collapse under the weight of the boar. Moreover, when a mating was taking place in the service pens, it was much more likely to be
Ž 2
interrupted by another boar than by another gilt 29.2% vs. 1.5%, x s151.7, dfs1,
.
p-0.001 .
Ž .
The mean TTFM was 2.27 "0.08 min with a range of 0.03 to 18.3 min, while the
Ž .
mean MA duration was 7.51 "0.16 min with a range of 0.34 to 35.98 min. Significant
Ž .
differences were found between boars in TTFM F10,588s5.98, p-0.001 , although
Ž .
there was no group effect, and in duration of MA F10,588s9.24, p-0.001 , where a
Ž .
group effect also existed F2,588s3.25, p-0.05 . Moreover, a significant correlation
Žrs q0.58, p-0.01 was identified between TTFM and duration of MA. However,.
Ž .
there was no correlation between the TTFM and TTGB rs y0.31, ps0.43 . Also, the TTFM did not differ significantly for the different classes of mating quality
ŽF4,596s2.01, ps0.09 , but the duration of MA differed significantly between the.
Ž .
mating quality classes F4,596s8.56, p-0.001 .
The quality of mating was strongly related to the degree of movement of the gilt
Ž 2 .
when the boar was on her back x s88.7, dfs16, p-0.001 and to the reason for
Ž 2 .
termination of the observed mating event x s119.4, dfs20, p-0.001 , indicating that interruption from other competitor boars and the inability of the gilt to support the
Ž .
boar’s weight when she terminated the mating event by lying down were most strongly linked to a mating of poor quality.
3.2. Diurnal pattern of mating eÕents
Mating events followed a diurnal pattern with a peak shortly after the feeding time
Ž0500 to 0600 h and early in the afternoon 1300 to 1400 h . The lowest number of. Ž . Ž
mating events was observed between 1900 and 2000 h only four MAs in the 54 days of
.
the study .
3.3. Boar mating dexterity
The difference in mating quality between and within the teams of boars was
Ž .
significant Fig. 2 . The old team and the new team of boars in pen A did not differ
Ž 2 .
significantly x s3.5, dfs2, ps0.17 but both achieved significantly better quality
Ž 2
results compared with the pen B team of boars x s44.6, dfs2, p-0.001 vs. pen A
2 .
old team and x s106.7, dfs2, p-0.001 vs. pen A new team . Also significant was
Ž 2
the difference between boars of the same team for pen A old team: x s21.8, dfs4,
p-0.001; for pen B team x2s15.6, dfs8, p-0.05; for pen A new team x2s20.2,
.
dfs8, p-0.01 .
3.4. Number of MAs and mating quality in each hour of oestrus
Only 6% of MAs were inappropriately directed to gilts outside their oestrous period, most commonly toward gilts newly introduced into the pen although all the gilts in the
study were synchronised to come into oestrus 6 to 8 days after entry. Also, one gilt appeared to have an abnormal oestrous pattern; she received and accepted continuous MAs for over a 10-day period, suggesting a physiological disorder.
The time course of MAs during oestrus are illustrated in Fig. 3. Gilts received a high number of MAs in the very first hour of their oestrus since, by definition, the first MA in the series defined oestrus onset. Subsequently, a strong negative correlation was found between the hours after first MA and the number of MAs that a gilt received per
Ž
Fig. 3. Number of mating events that gilts received and average mating quality in each hour of oestrus based
.
Ž .
hour rs y0.55, p-0.001 . The quality of the observed MAs during the first 3 h of oestrus was not good and it did not become satisfactory until the end of day 2
Žrs q0.38, p-0.005 , suggesting that early MAs occurred before full standing.
oestrus was established.
3.5. The relationship between social rank and reproductiÕe behaÕiour
The hierarchies in all the three teams of boars that participated in the study were linear. There was no significant correlation between boar social status and body weight.
Ž 2
Mating quality score achieved was influenced by social status x s35.8, dfs16,
.
p-0.01 , with results suggesting that high ranking boars tended to have poorer quality MA compared with their lower ranking team mates. Moreover, subordinate boars tended
Ž .
to have more frequent MAs number of MAsrdays of observation than their dominant team mates in the period of observation, although differences were not statistically
Ž .
significant F4,6s2.22, ps0.16 . Low ranking animals also tended to have longer
Ž .
MAs, but again this difference was not significant F4,6s0.83, ps0.55 . Finally, there were no significant differences between boars of different social status in TTFM
ŽF4,6s0.57, ps0.69 ..
3.6. Gilt lesion scores
As indicated in Fig. 4, gilt lesion scores reached a maximum just after entry and then
Ž .
declined to a level lower than the lesion scores they had prior to their entry . A significant negative correlation was found between the number of days that a gilt had
Ž .
spent in the service pen and her lesion score rs y0.75, p-0.05 . Mean lesion score did not differ between pens.
Video recordings showed that the newly entered gilts spent most of the time at a distance from the resident animals and their sleeping areas were distinctly different. This lasted for about a week until a new batch of gilts entered the mating pen and the fighting started again.
Ž .
Table 2
The total number of MA and number of ‘good’q‘ very good’ MA that a gilt received in the period she spent in
Ž
the service pens in relation to the PD result. Only continuous recordings have been taken into account 48
.
Eighty four percent of the 80 gilts in the study had a positive pregnancy diagnosis
ŽPD and 16% were negative. The proportion of negative PD animals differed signifi-.
Ž 2
cantly between groups, with pen A having 10r30 and pen B 3r37 x s4.5, dfs1,
.
p-0.05 . Gilts with a positive PD result had received more total MA and total
Ž
‘good’q‘ very good’ MA Ts2.33, p-0.05 and Ts2.25, p-0.05, respectively;
.
Table 2 . Gilts with a positive PD were also significantly heavier at the time of selection
Ž15–17 days before their entry into the service pen; Ts2.80, p-0.01 . However, there.
Ž .
was no significant difference in the age at entry Ts0.95, ps0.34 , or in the mean
Ž .
lesion scores per gilt between positive and negative gilts Ts0.51, ps0.33 .
4. Discussion
Of the 933 MAs observed in this study, 35% were classified as ‘ very poor’, whereas 18% and 9% were classified as ‘good’ and ‘ very good’, respectively. Other studies
ŽRikard-Bell, 1992; Grigoriadis, 1997 found different results, with a much higher.
proportion of good quality matings. A comparison between these and the present study
Ž
is not possible however, because of the difference in the nature of the criteria used i.e.,
. Ž
qualitative vs. quantitative and in the service systems examined i.e., conventional vs.
.
dynamic . It is to be expected that overall mating quality would be better in a conventional individual service system, since sows are not introduced to the boar until believed to be showing standing oestrus. Although in the dynamic service system, relatively few MAs occurred outside the oestrus period of the gilts, it seemed that many MAs were made during pro-oestrus when the gilts may have been giving olfactory andror behavioural indications of impending oestrus but not yet showing a full standing
Ž .
response. Shaw and Edwards 1995 , examining the mating efficiency in an outdoor multi-sire mating system for multiparous sows, reported quite similar results to the present study.
The mean boar first mount latency in this study was 2.27 min, which is much more than that observed in other investigations taking place in conventional mating systems
Ž43 s by Signoret, 1970; 41 s by Hemsworth et al., 1991; 39 s by Soede and Schouten, .
Ž
the current system, the animals had a number of influences from outside other boars,
.
oestrous gilts , which distracted the boar from the gilt and prolonged the first mount latency. Also, the dimensions of the service pens in this study were much bigger than a typical mating pen, thus the gilt could avoid mounting quite easily by running away when not in full standing oestrus.
The percentage of mating events, which were terminated by the gilt lying down, was as high as 27%. In these cases, the gilt could not support the weight of the boar and collapsed. Similar results have been found in an outdoor mating system by Shaw and
Ž .
Edwards 1995 . The boars used in the study were of various weights, ranging from 162 to 308 kg while the average gilt weight was 109 kg ranging from 95 to 115 kg. This difference makes it understandable why, in so many cases, the gilt could not support the weight of the boar, and highlights the need for a high replacement rate with young boars in such a system where boar feed intake cannot be controlled.
Mating events in this study followed a diurnal pattern with a major peak after feeding
Ž0900 h . This finding is not in agreement with Tanida et al. 1989 , who indicated that. Ž .
mounting activities in a multi-sire mating system were concentrated in the period between midnight and morning. The reason for this difference may lie in the high temperatures and different photoperiod under which Tanida et al. carried out their investigation, which may have discouraged the animals from sexual activities during the day.
The mating quality difference between individuals was significant in all the boar teams. Boars of the pen A new team achieved higher quality MAs compared with the
Ž .
other teams. These boars were of young age 11 months old and much more active than
Ž .
boars in pen B and the old team in pen A 14 and 16 months old, respectively . There is a need for longitudinal studies of a dynamic service system to verify this aspect.
There was no significant effect of boar social status on the mating frequency, the TTFM and the duration of mating event. However, there was a striking trend for low ranking boars to achieve more frequent, better quality and longer duration MAs than high ranking boars. Moreover, mating quality grade was related to the boar social status. A number of authors have reported that in the wild dominant boars have priority of
Ž .
access to all resources including mates Craig, 1986; Mendl et al., 1992 , but this does not seem the norm in the semi-intensive conditions of a dynamic service system. It may be that oestrous females were not considered to be a limiting resource in these circumstances, or that pair feeding tests are not the most appropriate method to decide the male reproductive hierarchy in a dynamic service system. Social and sexual status of the boars raised under these conditions, where they continuously have access to oestrous females, are two completely different parameters and they should not be confused. Mate
Ž .
preferences exhibited by females Tanida et al., 1991; Hemsworth et al., 1992 may play an important role in the organisation of sexual hierarchy in a team of boars.
In total, 84% of the observed gilts were PD tested positive while 16% were negative. These PD results are satisfactory compared with other studies examining animals treated
Ž .
in the same way Schilling and Cerne, 1972; Britt et al., 1987 and general UK data
ŽMLC, 1998 . Differences between pregnant and non pregnant animals in the number of.
total MAs and ‘good’q‘ very good’ MAs received were significant. These results
Ž . Ž .
Ž . Ž .
from Soede and Schouten 1991 and Grigoriadis 1997 , who stated that conception rate was independent of the quality of natural service. Examination of the pattern of MAs received by the PD negative gilts indicated that they had generally received a low number and poor quality MAs, although 90% of them had shown some sign of oestrous behaviour. However, some gilts had received good quality MAs, indicating that other factors, for example, boar fertility, had an influence on gilt pregnancy and might account for the difference between pens. Gilts that would later test positive were significantly
Ž .
heavier than negatives at selection 15–17 days prior to entry into the service pens . However, positive and negative tested gilts did not differ significantly in their age and mean lesion score. This latter finding indicates that the level of fighting in the service pens was not a major determinant of the gilt conception rate and is not in agreement
Ž . Ž .
with Mendl et al. 1992 and Simmins 1993 .
An increase in the recorded lesions was observed 3 days after entry due to intense fighting especially in the first 2 h after the new and old gilts first met. Then, they declined rapidly and remained relatively constant from 21 days onwards. These results
Ž
support findings from studies with group-housed females Arey and Jamieson, 1997,
. Ž
1998 and studies with female dynamic groups Spoolder et al., 1996; Rigat et al.,
.
1998 .
5. Conclusion
The dynamic service system for gilts is a valuable alternative in modern swine husbandry. It provides satisfactory mating efficiency and convenient mating manage-ment. Additional parameters in such a system should be taken into account, including individual boar size and mating dexterity, competition between boars, gilt age and weight at entry and level of fighting between old and newly introduced gilts, in order to optimise the obtained reproductive efficiency.
Acknowledgements
Ž .
Dimitris F. Grigoriadis is funded by the Greek State of Foundations IKY . We are grateful to A. Simmers Oldmeldrum, Aberdeenshire and the management and staff of the Cairnbrogie farm for their help and cooperation.
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