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The characterisation of suckling in wild boar
APPLIED ANIMAL BEHAVKXIR SCIENCE
EISEVIER:
Applied Animal Behaviour
The characterisation
Science 53 (1997) 271-277
of suckling in wild boar
Ian Horrell
’
Department of Psychology, Uniuersi@ of Hull, Hull HlJ6 7RX, UK Accepted 23 February
1996
Abstract Suckling was observed over a total of five lactations in two wild boar (SW scrofu L.) sows in semi-natural enclosures. A total of 61 suckling periods were recorded at four stages post-pxtum: 12-48 h, 6-8 days, 2-4 weeks, and 6-7 weeks. In contrast to a previous account, it was found that the detailed characteristics of suckling in wild boar were indistinguishable from those described in the domestic pig, with each suckling period having five phases, including a brief milk ejection phase lasting a mean of 19 s. Other timings of component stages were also comparable to those in the domestic pig. There were slight but significant tendencies for the durations of the pre-ejection phases and ejection itself to decline with increasing age of the litter. The duration of post-ejection stimulation fell sharply over the second and third weeks post-paxturn. In the two litters recorded, boarlets showed consistent teat preferences. 0 1997 Elsevier Science B.V. Keyvords: Pig-wild;
Suckling
behaviour;
Milk-ejection;
Weaning
1. Introduction It has long been known that suckling in the domestic pig is a much more complex affair than in species that give birth to only one or two young at a time, such as sheep and cattle, and that a great deal of coordinated massaging of the udder and sucking at teats is necessary before a brief period of milk ejection and flow (Gill and Thompson, 1956). The whole process has been characterised as falling into five phases: gathering and finding teat positions, massaging the udder, interspersed with periods of slow steady sucking which increasingly predominate, culminating in 15-20 s of rapid sucking movements coinciding with milk ejection, and a return to alternating periods of massage and slow sucking after let-down (Whittemore and Fraser, 1974; Fraser, 1980).
’ Tel. 01482-465282;
Fax. 01482-465599
016%1591/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PfI SO168-1591(96)01054-4
272
I. Howe.U/Appried
Animal Eehaviour Science 53 (1997) 271-277
Domestic pigs are generally thought to have been derived directly from wild boar (Sus scrofa L.) by selective breeding in the course of domestication. The morphology of the two are distinctly different. The most detailed observations of suckling in the European wild boar describe a rather simpler process than that in the domestic pig, with three phases and a period of milk ejection estimated at 45-55 s (Van Gundlach, 1%8). If there are specific differences in the milk ejection mechanism, it would give us some insight into its evolution. However, wild boar are shy and cryptic animals, and it is possible that previous observations have not been made in conditions that allow the necessary fine behavioural d&riminations. Moreover, those observations were before the 5 phase and the very brief period of milk flow had been clearly described (Whit¬e and Fraser, 1974). The present purpose was, first, to determine whether any basic characteristic of suckling in the wild boar is different from that in the domestic pig, and, secondly, to estimate the nature of developmental trends during the course of lactation.
2Method
Two female wild boar, offspring of animals captured in the Polish forests, were penned in two paddocks of approximately 0.3 ha each. They were normally run together with a male (sire of the litters). The paddocks were of rough pasture, with a number of large piles of branches from tree prunings, and, in one paddock, an old omhard in one comer. As well as the vegetation, each paddock had a 2 m X 3 m cormgated iron-roofed ark in which the animals almost always made their main nest. They were fed general animal concentrate in large nut form at a rate of 1.5 kg per adult day-‘. They became sufficiently accustomed to the presence of a human to take nuts out of the hand and accept, without any reaction, observers squatting in the doorway of the ark during suckling. Data were collected from the first two litters of one sow (N surviving boarlets 8 and 8, respectively) and the first three of the other (who bred twice in her frost breeding season: N = 2,6 and 5). observations were made on an opportunistic basis at random times throughout daylight hours. Gbservation periods typically lasted 1.5-5 h, during which the observer moved quietly around the paddock, keeping in close visual contact without disturbing the animals’ behaviour. At suckling, the following timings were taken, mainly by an observer with a stopwatch and experience of many hundred such recordings in domestic pig: times of start (at least 50% of the litter actively massaging the udder), peak grunt-rate, start of ejection, end of ejection, and termination of the suckling period (either sow turning over onto its udder, or more than 50% of boar-lets ceasing activity at the udder for at least 30 s). The timing of the grunt-rate peak was estimated by the experienced observers from the rapid rise in rate preceding it that was evident in both sows. The main criterion for ejection was the onset of the simultaneous switch to sustained fast sucking by all boarlets, with the fixed and ‘concentrated’ posture that goes with it. The subsequent occurrence of darting movements to other teats or return to massage, by most or all boat-lets in rapid succession was taken as confirmation of this: the time at which the first boarlet left the teat and others ceased fast sucking was
I. Howell/Applied
Animal Behaviour Science 53 (1997) 271-277
273
assumed to mark the end of milk flow and the onset of phase 5. Where these features were not seen, the suckling was classed as having failed to achieve ejection. A few sucklings were recorded with handheld video-recorder for future analysis. The cause of termination and other interesting events were also noted. Observations were concentrated into four periods of each lactation: 12-48 h postpartum, and with boarlets 1 week ( f 1 day), 2-4 weeks, or 6-7 weeks old. Summary descriptive statistics on each parameter of suckling were calculated for each age range. Comparisons between ages were made by submitting individual timings to the KruskalWallis one-way analysis of variance. Although the same litter and piglets were observed on a number of occasions, data were not systematically collected from each litter at each age, and the total number of sucklings observed at different ages varied. Therefore, a conservative estimate of the reliability of differences was made by employing a non-parametric model that made no assumption of repeated measures but accommodated unequal cell frequencies. One litter was ear-tagged in early lactation, for individual identification at a distance. Individuals could be distinguished by coat markings in the litter of two. Teat occupied at ejection by each boarlet was recorded for six sucklings at 4 or 6 weeks of age in the tagged litter and four times over 2 days in the small litter.
3. Ressdts Observers had no difficulty in getting close enough to litters to see clearly all the features that are chamcteristic of suckling in the domestic pig, without the animals showing any reaction. Furthermore, it was no mot-c or less problematic to discriminate the boundaries between the five phases, or to time all the other specific events that normaIly occur in the course of suckling in domestic pigs. Summary descriptive statistics for these timings are given in Table 1, in the form of means and &mdard errors. A few sucklings were seen at a distance or without the stopwatch, such that the time and occurrence of letdown could be recorded, but not the detailed timings of component stages. Occasionally, a particular component timing was missed. As a result, the numbers of recordings of each parameter are not all equal. Therefore, the number of incidents contributing to each mean is also given. At least some data were collected from a total of 61 sucklings, and every measure from 49. Each summary statistic in the table in-rated data from at least three different sow-lactations. The frequency of suckling is given by the mean interval between sucklings involving milk ejection. The number of observations of this was necessarily much less than for the parameters of the sucklings themselves, because two sucklings have to be seen for the interval between them to be known with cermimy. To extend the number of units of data contributing as well as giving the mean of all intervals actually observed from beginning to end, the table also gives a statistic incorporating the interval from the start of observation to the first suckling. This was based on the assumption that, if observations started at random they would begin, on average, half way between two sucklings.
274
I. Horrell /Applied Animal Behaviour Science 53 (1997) 271-277
Table 1 Mean timings and total number of events (with, in parentheses, standard error)
Interval between ejections (min) Interval between ejections incl. delay to first observed (min) Latency (s) from initiation to: Grunt-rate peak Duration (s) of: Phase 3 Phase 4 (ejection) Phase 5 (after stimulation) Total duration of sucklings (s) Causes of termination: Mother Young No. of ejections observed No. of ‘false’ sucklings
the number of observations
followed
First 48 h
6-8 days
2-4 weeks
6-7 weeks
53.3 (6; 9.77) 46.9 (9; 7.51)
42.2 (5; 2.42) 44.6 (7; 6.89)
91.3 (9; 6.70) 95.3 (19; 7.13)
86.1 (8; 21.26) 105.6 (11; 11.28)
111.0 (7; 13.16)
79.2 (11; 12.10)
84.8 (21; 5.18)
70.0 (11; 6.30)
27.7 (7; 3.59) 21.9 (8; 1.68) 123.4 (8; 17.51) 272.8 (9; 22.17)
24.0 (11; 3.23) 19.2 (13; 0.86) 115.7 (13; 29.61) 236.8 (13; 29.27)
17.9 (20; 0.83) 17.7 (21; 0.70) 22.4 (21; 1.79) 143.5 (21; 5.30)
19.6 (11; 2.11) 18.0 (11; 1.07) 33.3 (11; 7.15) 141.0 (11; 8.07)
3 8 12 2
10 5 15 2
21 1 22 1
11 0 12 0
by the
Therefore, each latency from the start of observation to the first suckling was doubled and included as a sample of the interval between sucklings. It can be seen from Table 1 that the inter-suckling interval was around 50 min over the first week but had risen to 90 min by 2-4 weeks, and that the two different estimates described above agreed fairly closely. The mean interval did not increase further to 6-7 weeks. However, the mean hides two very different trends: two litters observed in early spring were still suckling at regular 60-70 min intervals, while a litter seen in late summer, the second to that sow in the year, had almost weaned by this age, with some intervals over 3 h. The data on the latency from the initiation of suckling to the various transitions between stages show that latency to milk letdown declined relatively sharply over the first week and slowly with age thereafter (H = 7.73, P = .OSl>. The total duration of suckling (‘latency to termination of suckling’) also declined with age, with a very sharp reduction between 1 week and 2-4 weeks. Underlying these trends in overall timings are modest but fairly steady reductions with age in the durations of phases 1 and 2 together (gathering at the udder and massaging with bouts of slow sucking), the latency from the sharp rise in grunt-rate to the initiation of ejection (H = 8.41, P < .OS> and phase 4 (milk flow) (N.S.). However, the final phase (5: return to massage after letdown) showed a very sharp reduction in length between 1 and 2-4 weeks post-partum (F = 32.09, P < .OOl>. This accounts for most of the change in overall suckling duration.
I. Horrell/Applied
Animal Behauiour Science 53 (1997) 271-277
275
All these data were derived from sucklings involving ejection, with ‘false’ sucklings excluded. The numbers of such sucklings without letdown are also given in Table 1. There were a few in young litters, but only one was seen in 35 sucklings by litters of 2 weeks of age or more. Another age trend, characteristic of domestic pigs and most other mammals, is the increasing tendency for sucklings to be terminated actively by the sow: for most sucklings in the first 48 h post-partum, the sow lay until boarlets had ceased suckling spontaneously, but only one suckling observed in litters of 2 weeks or older ended this way. The two boarlets in the small litter each occupied the same teat on all four sucklings recorded. In the tagged litter of six, two animals sucked at the same teat on all six, three on five and the sixth on four of the recorded sucklings. These results would be unlikely to occur by chance : on the simplifying and conservative assumption that only two and six teats, respectively, are available, P = l/64 in the first case and P < < ,001 in the second, by basic probability theory.
4. Discussion It was clear to the experienced observer from the very first observations that the basic character of suckling in wild boar was the same as in the domestic pig (Whittemore and Fraser, 1974), with the normal five phases clearly delineated and all specific features present. At a quantitative level, the timings and the age trends found are consistent with those recorded for domestic pigs in similar naturalistic conditions (Newberry and Wood-Gush, 1985; Jensen, 1988; Jensen and Recen, 1989). In the pig, mean inter-suckling intervals of 46-70 min have been found over the first week, rising through 63-70 at 4 weeks, to 73-86 at 6-8 weeks and still higher as weaning is approached. The duration of the pre-ejection period (latency to letdown) in pigs, the latency between grunt peak and milk ejection, and the period of ejection itself have generally been reported to remain stable through lactation, at 70-90 s, 22-27 s and 13-17 s, respectively (the range of mean figures given in the literature for these parameters). The general level of these timings for wild boar were close to these values, although a small but significant decline with age was seen here in all these timings. Note that the latency from accelerating grunt rate to ejection onset cannot strictly be equated with phase 3 as defined by the proportion of piglets sucking (Whittemore and Fraser, 1974) or by the period of bursts of fast sucking (Rushen and Fraser, 1990) though it approximates it. A decline in the duration of ejection itself over the first 6 weeks of lactation has been documented in indoor pigs (Gill and Thompson, 1956) and the absence of these trends in other reports may be due to the fact that the largest changes occur in the first week, and others have not generally collected data in that early period. The final phase, of post-ejection stimulation, in wild boar was somewhat shorter than seen in extensive domestic pigs, where mean values of 155-235 s have been recorded over the first week (Newberry and Wood-Gush, 1985; Jensen, 1988; Jensen and Recen. 1989). It also fell rather more sharply, and earlier in lactation, than in the pig, where durations of 50-75 s were still obtained at 4 weeks in the latter case. This reduction follows from the rapidly increasing tendency for the sow to rise soon after letdown, seen
216
I. Horrell/ Applied Animal Behaviour Science 53 (1997) 271-277
also in domestic pigs, and may reflect a stronger inherent tendency in the wild boar mother to impose weaning, a suggestion supported by the fact that one 6-week-old summer-born litter was seen to suckle only three times in over 11 h of observation. However, two litters observed in the following spring were still suckling fairly regularly at about hourly intervals at 6 weeks. Further, the post-ejection massage lasted consistently longer in the spring than in the summer litters (mean 40.0 vs. 15.7 s, respectively). It is more likely that particular environmental constraints, such as the poorer nutritional status of a sow having a second litter in the summer (not common in wild boar) or varying accessibility of alternative food sources, may form the basis of slight differences in weaning trends. Overall, the minor differences in timings and trends between those seen here and those reported in the domestic pig can be attributed to particular conditions of observation rather than to inherent characteristics of the animals. Thus, in contrast to the only previous quantitative account of suckling in wild boar (Van Gundlach, 1968), which was written before definition of the distinction between phases 2 and 3 in domestic piag, we conclude that the process is essentially identical to that in the pig. The probable explanation of the ‘three-phase’ account of Von Gundlach (1968) is a failure to distinguish between phase 3 and phase 4, and an assumption that the steady slow-sucking of phase 3, with animals almost continuously fixed to the teat and occasional bursts of fast sucking, indicates milk flow just as much as the sustained fast sucking of phase 4. If we combine our estimates for phases 3 and 4 and add a little to allow for the fact that steady slow sucking may begin in the rising grunt-rate phase, before the peak, we approximate his estimate of about 50 s of milk flow. From the limited data, it seems that individual teat preferences develop as strongly in wild boar as in domestic pigs. Further, the two sows observed here showed a remarkable degree of social coordination in suckling. They gave birth to litters 7 days apart in March 1995. Five sucklings were observed in each when their litters were 3 and 4 weeks old, respectively, and 4 when they were 6 and 7 weeks old. Gn one occasion, when one sow started suckling, it took 106 s for the other, reacting to suckling grunts, to run 30 m and join her in suckling in the ark; on all eight other occasions, the second sow started suckling within 60 s of the first. Moreover, on all occasions, they were either in the ark together or in direct physical contact in the open. Some synchrony has been reported in domestic pigs (Newberry and Wood-Gush, 1985) but not to this extent. The proportion of sucklings that do not achieve milk ejection (l/35 in litters greater than 1 week old), was much smaller than that commonly reported for domestic pigs (22-35s: Newbetry and Wood-Gush, 1985; Fraser, 1977; Ellendorff et al., 1982). However, some individual domestic sows show very few, and the sample of wild boar is much too small to assume that they are, in general, more efficient in this respect.
Acknowledgements I wish to thank Michael Horrell for cooperation in maintenance wild boar and Philippa A’Ness for help in collecting data.
of the herd of seven
I. Howell/Applied
Animal Behaaiour Science 53 (19971271-277
717
References Ellendotff, F., Forsling, M.L. and Poulain, D.A., 1982. The milk ejection reflex in the pig. J. Physiol. , 333: 577-594. Fraser, D., 1977. Some behavioural aspects of milk ejection failure by sows Br. Vet. J., 133: 126-133. Fraser, D.. 1980. A review of the behavioural mechanism of milk ejection of the domestic pig. Appl. Anim. Ethel., 6: 247-255. Gill, J.C. and Thompson, W., 1956. Observations on the behaviour of suckling pigs. Br. J. Anim. Behav.. 4: 46-5 1. Jensen, P., 1988. Maternal behaviour and mother-young interactions during lactation in free-ranging domestic pigs. Appl. Anim. Behav. Sci., 20: 297-303. Jensen, P. and Recen, B., 1989. When to wean-observations from free-ranging domestic pigs. Appl. Anim. Behav. Sci., 23: 49-60. Newberry, R. and Wood-Gush, D.G.M., 1986. The suckling behaviour of domestic pigs in a semi-natural environment. Behaviour, 95: 1 l-25. Rushen, J. and Fraser, D., 1990. Nutritive and non-nutririve sucking and the temporal organisation of the suckling behaviour of domestic piglets. Dev. Psychobiol., 22: 789-801. Von Gundlach, H., 1968. Brutfiirsorge, Brutplfege. Verhaltensontogenese und Tagesperiodik beim Europlischen Wildschwein (Sus scrofu L.). 2. Tierpsychol.. 25: 955-995. Whittemore, C.T. and Fraser, D., 1974. The nursing and suckling behaviour of pigs. II. Vocalizations of the sow in relation to suckling behaviour and milk ejection. Br. Vet. J., 130: 346-356
EISEVIER:
Applied Animal Behaviour
The characterisation
Science 53 (1997) 271-277
of suckling in wild boar
Ian Horrell
’
Department of Psychology, Uniuersi@ of Hull, Hull HlJ6 7RX, UK Accepted 23 February
1996
Abstract Suckling was observed over a total of five lactations in two wild boar (SW scrofu L.) sows in semi-natural enclosures. A total of 61 suckling periods were recorded at four stages post-pxtum: 12-48 h, 6-8 days, 2-4 weeks, and 6-7 weeks. In contrast to a previous account, it was found that the detailed characteristics of suckling in wild boar were indistinguishable from those described in the domestic pig, with each suckling period having five phases, including a brief milk ejection phase lasting a mean of 19 s. Other timings of component stages were also comparable to those in the domestic pig. There were slight but significant tendencies for the durations of the pre-ejection phases and ejection itself to decline with increasing age of the litter. The duration of post-ejection stimulation fell sharply over the second and third weeks post-paxturn. In the two litters recorded, boarlets showed consistent teat preferences. 0 1997 Elsevier Science B.V. Keyvords: Pig-wild;
Suckling
behaviour;
Milk-ejection;
Weaning
1. Introduction It has long been known that suckling in the domestic pig is a much more complex affair than in species that give birth to only one or two young at a time, such as sheep and cattle, and that a great deal of coordinated massaging of the udder and sucking at teats is necessary before a brief period of milk ejection and flow (Gill and Thompson, 1956). The whole process has been characterised as falling into five phases: gathering and finding teat positions, massaging the udder, interspersed with periods of slow steady sucking which increasingly predominate, culminating in 15-20 s of rapid sucking movements coinciding with milk ejection, and a return to alternating periods of massage and slow sucking after let-down (Whittemore and Fraser, 1974; Fraser, 1980).
’ Tel. 01482-465282;
Fax. 01482-465599
016%1591/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PfI SO168-1591(96)01054-4
272
I. Howe.U/Appried
Animal Eehaviour Science 53 (1997) 271-277
Domestic pigs are generally thought to have been derived directly from wild boar (Sus scrofa L.) by selective breeding in the course of domestication. The morphology of the two are distinctly different. The most detailed observations of suckling in the European wild boar describe a rather simpler process than that in the domestic pig, with three phases and a period of milk ejection estimated at 45-55 s (Van Gundlach, 1%8). If there are specific differences in the milk ejection mechanism, it would give us some insight into its evolution. However, wild boar are shy and cryptic animals, and it is possible that previous observations have not been made in conditions that allow the necessary fine behavioural d&riminations. Moreover, those observations were before the 5 phase and the very brief period of milk flow had been clearly described (Whit¬e and Fraser, 1974). The present purpose was, first, to determine whether any basic characteristic of suckling in the wild boar is different from that in the domestic pig, and, secondly, to estimate the nature of developmental trends during the course of lactation.
2Method
Two female wild boar, offspring of animals captured in the Polish forests, were penned in two paddocks of approximately 0.3 ha each. They were normally run together with a male (sire of the litters). The paddocks were of rough pasture, with a number of large piles of branches from tree prunings, and, in one paddock, an old omhard in one comer. As well as the vegetation, each paddock had a 2 m X 3 m cormgated iron-roofed ark in which the animals almost always made their main nest. They were fed general animal concentrate in large nut form at a rate of 1.5 kg per adult day-‘. They became sufficiently accustomed to the presence of a human to take nuts out of the hand and accept, without any reaction, observers squatting in the doorway of the ark during suckling. Data were collected from the first two litters of one sow (N surviving boarlets 8 and 8, respectively) and the first three of the other (who bred twice in her frost breeding season: N = 2,6 and 5). observations were made on an opportunistic basis at random times throughout daylight hours. Gbservation periods typically lasted 1.5-5 h, during which the observer moved quietly around the paddock, keeping in close visual contact without disturbing the animals’ behaviour. At suckling, the following timings were taken, mainly by an observer with a stopwatch and experience of many hundred such recordings in domestic pig: times of start (at least 50% of the litter actively massaging the udder), peak grunt-rate, start of ejection, end of ejection, and termination of the suckling period (either sow turning over onto its udder, or more than 50% of boar-lets ceasing activity at the udder for at least 30 s). The timing of the grunt-rate peak was estimated by the experienced observers from the rapid rise in rate preceding it that was evident in both sows. The main criterion for ejection was the onset of the simultaneous switch to sustained fast sucking by all boarlets, with the fixed and ‘concentrated’ posture that goes with it. The subsequent occurrence of darting movements to other teats or return to massage, by most or all boat-lets in rapid succession was taken as confirmation of this: the time at which the first boarlet left the teat and others ceased fast sucking was
I. Howell/Applied
Animal Behaviour Science 53 (1997) 271-277
273
assumed to mark the end of milk flow and the onset of phase 5. Where these features were not seen, the suckling was classed as having failed to achieve ejection. A few sucklings were recorded with handheld video-recorder for future analysis. The cause of termination and other interesting events were also noted. Observations were concentrated into four periods of each lactation: 12-48 h postpartum, and with boarlets 1 week ( f 1 day), 2-4 weeks, or 6-7 weeks old. Summary descriptive statistics on each parameter of suckling were calculated for each age range. Comparisons between ages were made by submitting individual timings to the KruskalWallis one-way analysis of variance. Although the same litter and piglets were observed on a number of occasions, data were not systematically collected from each litter at each age, and the total number of sucklings observed at different ages varied. Therefore, a conservative estimate of the reliability of differences was made by employing a non-parametric model that made no assumption of repeated measures but accommodated unequal cell frequencies. One litter was ear-tagged in early lactation, for individual identification at a distance. Individuals could be distinguished by coat markings in the litter of two. Teat occupied at ejection by each boarlet was recorded for six sucklings at 4 or 6 weeks of age in the tagged litter and four times over 2 days in the small litter.
3. Ressdts Observers had no difficulty in getting close enough to litters to see clearly all the features that are chamcteristic of suckling in the domestic pig, without the animals showing any reaction. Furthermore, it was no mot-c or less problematic to discriminate the boundaries between the five phases, or to time all the other specific events that normaIly occur in the course of suckling in domestic pigs. Summary descriptive statistics for these timings are given in Table 1, in the form of means and &mdard errors. A few sucklings were seen at a distance or without the stopwatch, such that the time and occurrence of letdown could be recorded, but not the detailed timings of component stages. Occasionally, a particular component timing was missed. As a result, the numbers of recordings of each parameter are not all equal. Therefore, the number of incidents contributing to each mean is also given. At least some data were collected from a total of 61 sucklings, and every measure from 49. Each summary statistic in the table in-rated data from at least three different sow-lactations. The frequency of suckling is given by the mean interval between sucklings involving milk ejection. The number of observations of this was necessarily much less than for the parameters of the sucklings themselves, because two sucklings have to be seen for the interval between them to be known with cermimy. To extend the number of units of data contributing as well as giving the mean of all intervals actually observed from beginning to end, the table also gives a statistic incorporating the interval from the start of observation to the first suckling. This was based on the assumption that, if observations started at random they would begin, on average, half way between two sucklings.
274
I. Horrell /Applied Animal Behaviour Science 53 (1997) 271-277
Table 1 Mean timings and total number of events (with, in parentheses, standard error)
Interval between ejections (min) Interval between ejections incl. delay to first observed (min) Latency (s) from initiation to: Grunt-rate peak Duration (s) of: Phase 3 Phase 4 (ejection) Phase 5 (after stimulation) Total duration of sucklings (s) Causes of termination: Mother Young No. of ejections observed No. of ‘false’ sucklings
the number of observations
followed
First 48 h
6-8 days
2-4 weeks
6-7 weeks
53.3 (6; 9.77) 46.9 (9; 7.51)
42.2 (5; 2.42) 44.6 (7; 6.89)
91.3 (9; 6.70) 95.3 (19; 7.13)
86.1 (8; 21.26) 105.6 (11; 11.28)
111.0 (7; 13.16)
79.2 (11; 12.10)
84.8 (21; 5.18)
70.0 (11; 6.30)
27.7 (7; 3.59) 21.9 (8; 1.68) 123.4 (8; 17.51) 272.8 (9; 22.17)
24.0 (11; 3.23) 19.2 (13; 0.86) 115.7 (13; 29.61) 236.8 (13; 29.27)
17.9 (20; 0.83) 17.7 (21; 0.70) 22.4 (21; 1.79) 143.5 (21; 5.30)
19.6 (11; 2.11) 18.0 (11; 1.07) 33.3 (11; 7.15) 141.0 (11; 8.07)
3 8 12 2
10 5 15 2
21 1 22 1
11 0 12 0
by the
Therefore, each latency from the start of observation to the first suckling was doubled and included as a sample of the interval between sucklings. It can be seen from Table 1 that the inter-suckling interval was around 50 min over the first week but had risen to 90 min by 2-4 weeks, and that the two different estimates described above agreed fairly closely. The mean interval did not increase further to 6-7 weeks. However, the mean hides two very different trends: two litters observed in early spring were still suckling at regular 60-70 min intervals, while a litter seen in late summer, the second to that sow in the year, had almost weaned by this age, with some intervals over 3 h. The data on the latency from the initiation of suckling to the various transitions between stages show that latency to milk letdown declined relatively sharply over the first week and slowly with age thereafter (H = 7.73, P = .OSl>. The total duration of suckling (‘latency to termination of suckling’) also declined with age, with a very sharp reduction between 1 week and 2-4 weeks. Underlying these trends in overall timings are modest but fairly steady reductions with age in the durations of phases 1 and 2 together (gathering at the udder and massaging with bouts of slow sucking), the latency from the sharp rise in grunt-rate to the initiation of ejection (H = 8.41, P < .OS> and phase 4 (milk flow) (N.S.). However, the final phase (5: return to massage after letdown) showed a very sharp reduction in length between 1 and 2-4 weeks post-partum (F = 32.09, P < .OOl>. This accounts for most of the change in overall suckling duration.
I. Horrell/Applied
Animal Behauiour Science 53 (1997) 271-277
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All these data were derived from sucklings involving ejection, with ‘false’ sucklings excluded. The numbers of such sucklings without letdown are also given in Table 1. There were a few in young litters, but only one was seen in 35 sucklings by litters of 2 weeks of age or more. Another age trend, characteristic of domestic pigs and most other mammals, is the increasing tendency for sucklings to be terminated actively by the sow: for most sucklings in the first 48 h post-partum, the sow lay until boarlets had ceased suckling spontaneously, but only one suckling observed in litters of 2 weeks or older ended this way. The two boarlets in the small litter each occupied the same teat on all four sucklings recorded. In the tagged litter of six, two animals sucked at the same teat on all six, three on five and the sixth on four of the recorded sucklings. These results would be unlikely to occur by chance : on the simplifying and conservative assumption that only two and six teats, respectively, are available, P = l/64 in the first case and P < < ,001 in the second, by basic probability theory.
4. Discussion It was clear to the experienced observer from the very first observations that the basic character of suckling in wild boar was the same as in the domestic pig (Whittemore and Fraser, 1974), with the normal five phases clearly delineated and all specific features present. At a quantitative level, the timings and the age trends found are consistent with those recorded for domestic pigs in similar naturalistic conditions (Newberry and Wood-Gush, 1985; Jensen, 1988; Jensen and Recen, 1989). In the pig, mean inter-suckling intervals of 46-70 min have been found over the first week, rising through 63-70 at 4 weeks, to 73-86 at 6-8 weeks and still higher as weaning is approached. The duration of the pre-ejection period (latency to letdown) in pigs, the latency between grunt peak and milk ejection, and the period of ejection itself have generally been reported to remain stable through lactation, at 70-90 s, 22-27 s and 13-17 s, respectively (the range of mean figures given in the literature for these parameters). The general level of these timings for wild boar were close to these values, although a small but significant decline with age was seen here in all these timings. Note that the latency from accelerating grunt rate to ejection onset cannot strictly be equated with phase 3 as defined by the proportion of piglets sucking (Whittemore and Fraser, 1974) or by the period of bursts of fast sucking (Rushen and Fraser, 1990) though it approximates it. A decline in the duration of ejection itself over the first 6 weeks of lactation has been documented in indoor pigs (Gill and Thompson, 1956) and the absence of these trends in other reports may be due to the fact that the largest changes occur in the first week, and others have not generally collected data in that early period. The final phase, of post-ejection stimulation, in wild boar was somewhat shorter than seen in extensive domestic pigs, where mean values of 155-235 s have been recorded over the first week (Newberry and Wood-Gush, 1985; Jensen, 1988; Jensen and Recen. 1989). It also fell rather more sharply, and earlier in lactation, than in the pig, where durations of 50-75 s were still obtained at 4 weeks in the latter case. This reduction follows from the rapidly increasing tendency for the sow to rise soon after letdown, seen
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also in domestic pigs, and may reflect a stronger inherent tendency in the wild boar mother to impose weaning, a suggestion supported by the fact that one 6-week-old summer-born litter was seen to suckle only three times in over 11 h of observation. However, two litters observed in the following spring were still suckling fairly regularly at about hourly intervals at 6 weeks. Further, the post-ejection massage lasted consistently longer in the spring than in the summer litters (mean 40.0 vs. 15.7 s, respectively). It is more likely that particular environmental constraints, such as the poorer nutritional status of a sow having a second litter in the summer (not common in wild boar) or varying accessibility of alternative food sources, may form the basis of slight differences in weaning trends. Overall, the minor differences in timings and trends between those seen here and those reported in the domestic pig can be attributed to particular conditions of observation rather than to inherent characteristics of the animals. Thus, in contrast to the only previous quantitative account of suckling in wild boar (Van Gundlach, 1968), which was written before definition of the distinction between phases 2 and 3 in domestic piag, we conclude that the process is essentially identical to that in the pig. The probable explanation of the ‘three-phase’ account of Von Gundlach (1968) is a failure to distinguish between phase 3 and phase 4, and an assumption that the steady slow-sucking of phase 3, with animals almost continuously fixed to the teat and occasional bursts of fast sucking, indicates milk flow just as much as the sustained fast sucking of phase 4. If we combine our estimates for phases 3 and 4 and add a little to allow for the fact that steady slow sucking may begin in the rising grunt-rate phase, before the peak, we approximate his estimate of about 50 s of milk flow. From the limited data, it seems that individual teat preferences develop as strongly in wild boar as in domestic pigs. Further, the two sows observed here showed a remarkable degree of social coordination in suckling. They gave birth to litters 7 days apart in March 1995. Five sucklings were observed in each when their litters were 3 and 4 weeks old, respectively, and 4 when they were 6 and 7 weeks old. Gn one occasion, when one sow started suckling, it took 106 s for the other, reacting to suckling grunts, to run 30 m and join her in suckling in the ark; on all eight other occasions, the second sow started suckling within 60 s of the first. Moreover, on all occasions, they were either in the ark together or in direct physical contact in the open. Some synchrony has been reported in domestic pigs (Newberry and Wood-Gush, 1985) but not to this extent. The proportion of sucklings that do not achieve milk ejection (l/35 in litters greater than 1 week old), was much smaller than that commonly reported for domestic pigs (22-35s: Newbetry and Wood-Gush, 1985; Fraser, 1977; Ellendorff et al., 1982). However, some individual domestic sows show very few, and the sample of wild boar is much too small to assume that they are, in general, more efficient in this respect.
Acknowledgements I wish to thank Michael Horrell for cooperation in maintenance wild boar and Philippa A’Ness for help in collecting data.
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References Ellendotff, F., Forsling, M.L. and Poulain, D.A., 1982. The milk ejection reflex in the pig. J. Physiol. , 333: 577-594. Fraser, D., 1977. Some behavioural aspects of milk ejection failure by sows Br. Vet. J., 133: 126-133. Fraser, D.. 1980. A review of the behavioural mechanism of milk ejection of the domestic pig. Appl. Anim. Ethel., 6: 247-255. Gill, J.C. and Thompson, W., 1956. Observations on the behaviour of suckling pigs. Br. J. Anim. Behav.. 4: 46-5 1. Jensen, P., 1988. Maternal behaviour and mother-young interactions during lactation in free-ranging domestic pigs. Appl. Anim. Behav. Sci., 20: 297-303. Jensen, P. and Recen, B., 1989. When to wean-observations from free-ranging domestic pigs. Appl. Anim. Behav. Sci., 23: 49-60. Newberry, R. and Wood-Gush, D.G.M., 1986. The suckling behaviour of domestic pigs in a semi-natural environment. Behaviour, 95: 1 l-25. Rushen, J. and Fraser, D., 1990. Nutritive and non-nutririve sucking and the temporal organisation of the suckling behaviour of domestic piglets. Dev. Psychobiol., 22: 789-801. Von Gundlach, H., 1968. Brutfiirsorge, Brutplfege. Verhaltensontogenese und Tagesperiodik beim Europlischen Wildschwein (Sus scrofu L.). 2. Tierpsychol.. 25: 955-995. Whittemore, C.T. and Fraser, D., 1974. The nursing and suckling behaviour of pigs. II. Vocalizations of the sow in relation to suckling behaviour and milk ejection. Br. Vet. J., 130: 346-356