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Ewe–ewe and ewe–lamb behaviour in a hill and a lowland breed of sheep: a study using embryo transfer
Applied Animal Behaviour Science 61 Ž1999. 319–334
Ewe–ewe and ewe–lamb behaviour in a hill and a lowland breed of sheep: a study using embryo transfer C.M. Dwyer ) , A.B. Lawrence BehaÕioural Sciences Department, Animal Biology DiÕision, SAC, King’s Buildings, West Mains Road, Edinburgh, EH9 3JG, UK Accepted 20 July 1998
Abstract Domestic sheep have a strong social tendency. The nature of this gregariousness, however, varies with season, breed, sex and age. In this study the social behaviour of two breeds of ewe ŽSuffolk and Scottish Blackface. was investigated over two years in two different environments. In addition, to examine whether lamb behaviour would affect the behaviour of the ewe, an embryo transfer study was carried out between the two breeds resulting in four combinations of ewe and lamb ŽBlackface ewe with Blackface lamb, n s 25; Blackface ewe with Suffolk lamb, n s 24; Suffolk ewe with Suffolk lamb, n s 25; Suffolk ewe with Suffolk lamb, n s 25.. All ewes and lambs grazed together in Field 1 Žyear 1. and Field 2 Žyear 2.. Field 1 was 9 ha and rather uniform; Field 2 was 21.4 ha and had two distinct regions: an upland and a lowland area. Blackface ewes preferentially associated with their own lamb whereas Suffolk ewes associated equally with their own lamb or another Suffolk ewe, there was no effect of lamb breed Žpercent observations with own lamb as nearest neighbour, Field 1: Blackface ewes s 50.2%, Suffolk ewes s 43.5%, P - 0.05; Field 2: Blackface ewes s 73.1%, Suffolk ewes s 43.5%, P - 0.001.. Blackface ewes were also significantly closer to their lambs than Suffolk ewes, regardless of year or lamb breed ŽBlackface ewes s 6.10 m, Suffolk ewes s 11.54 m, P - 0.001.. When own lamb was not the nearest neighbour ewes associated with other ewes of the same breed as themselves ŽWith same-breed ewe s 88.4% of observations, with other-breed ewe s 11.6%, P - 0.001.. In Field 1 the distribution of both breeds in the field was similar to one another but ewes maintained subgroups composed predominantly of their own breed Ž P - 0.001.. The mean distance between ewes was the same for both breeds, however subgroups were significantly smaller for Blackface ewes Ž7.53 and 9.26 ewes for Blackface and Suffolk respectively, P - 0.001.. In Field 2
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0168-1591r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 1 5 9 1 Ž 9 8 . 0 0 2 0 3 - 2
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Blackface ewes were found mainly in the upland region of the field whereas Suffolk ewes were almost exclusively in the lowland areas. Mean distance between ewes increased markedly for Blackface ewes when compared to ewe–ewe distance in Field 1 but was unchanged for Suffolks Ž11.29 vs. 4.36 m for Blackface and Suffolk ewes respectively, P - 0.001.. Subgroup size also declined for Blackface ewes in comparison to Field 1 but increased for Suffolks ŽBlackfaces 3.10, Suffolks 11.31 ewes, P - 0.001.. Lamb breed had no effect on the social behaviour of either breed of ewe. The two breeds had differing behaviour in their relationship to their own lamb. Their relationship to other ewes, however, was significantly modified by the environment although the Blackface breed was less gregarious than the Suffolk under both conditions. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Sheep; Social behaviour; Spatial associations; Breed; Influence
1. Introduction Domestic sheep exhibit strong flocking behaviour, and maintain close spatial and social contacts with other sheep ŽLynch et al., 1992.. However, the nature of these contacts does not appear to be rigid. The social behaviour of both wild and domestic sheep varies seasonally. For example a mixed-age flock of Scottish Blackface ewes occupied a larger home range during the summer months than in the winter ŽLawrence and Wood-Gush, 1988., and social group size changed in the summer in Cyprus Mouflon ŽMaisels, 1993.. The age, sex and composition of the flock also affect the expression of social behaviour in both wild, feral and domestic sheep Že.g., Soay: Grubb and Jewell, 1966; Merino: Arnold and Pahl, 1974; Stolba et al., 1990; Mouflon: Le Pendu et al., 1996.. In addition, several authors report breed differences in the closeness and variety of social contact with, for example, Merino sheep forming close associations in contrast to the sub-grouping seen in other breeds ŽWinfield and Mullaney, 1973; Arnold et al., 1981; Shillito-Walser and Hague, 1981.. The environment in which sheep are placed can also have an effect on social behaviour ŽMcBride et al., 1967., with a greater degree of alertness shown in barren environments by Merinos ŽStolba et al., 1990. and a change in the frequency of some behaviours, especially play, between mountain and desert-living Bighorn sheep ŽBerger, 1979.. In the present study the social relationships of two breeds of sheep were investigated whilst grazing with lambs at foot: a lowland breed ŽSuffolk. and a hill breed ŽScottish Blackface.. The effect of environment on the nature of their social behaviour was examined as previous studies suggest that a more diverse environment may encourage the expression of greater variability in social behaviour ŽLynch, 1967; Stolba et al., 1990.. Reported differences in the social behaviour of hill and intensively husbanded sheep ŽWinfield and Mullaney, 1973; Arnold et al., 1981; Shillito-Walser and Hague, 1981. may be partly attributable to the field types encountered by the breeds under normal husbandry conditions. The behaviour of the lambs of the two breeds of sheep has already been shown to differ in the neonatal period ŽDwyer et al., 1996.. As these differences may persist and the behaviour of the young may affect the behaviour of the ewe, as has been suggested for ewes raising cross-fostered goat kids ŽKilgour, 1972., an
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embryo transfer study was also carried out between the two breeds to distinguish between maternal and lamb effects on social behaviour. Thus the effects of ewe breed, lamb breed and environmental diversity on the expression of social behaviour in ewes were investigated. A preliminary report of some of these results has already been published ŽDwyer and Lawrence, 1997..
2. Materials and methods 2.1. Animals Ewes were of a hill ŽScottish Blackface. or a lowland ŽSuffolk. breed and were aged 3 Žyears 1 and 2. or 4 years Žyear 2 only.. Ewes had previously been obtained from a number of different flocks as 1-year-olds. All ewes were multiparous and in their second or third parity. In year 1 40 animals were used Ž20 each of Suffolk and Blackface.; in year 2 60 animals were observed Ž30 of each breed.. Ewes were given single embryos by embryo transfer in both years. Donor ewes were super-ovulated, by injection of ovine FSH ŽOvagen, Immuno-Chemical Products, Auckland, NZ., and inseminated by laparoscopic artificial insemination with fresh semen using the technique described by McKelvey et al. Ž1985a.. Embryos were recovered on day 6 following insemination and transferred laparoscopically to synchronised recipient ewes, using the procedure of McKelvey et al. Ž1985b.. Embryos were transferred across breeds such that equal numbers of the possible breed combinations were obtained: Blackface ewes with Blackface lambs ŽBB, total n s 25., Blackface ewes with Suffolk lambs ŽBS, n s 25., Suffolk ewes with Suffolk lambs ŽSS, n s 25., and Suffolk ewes with Blackface lambs ŽSB, n s 25.. Ewes lambed indoors in April 1995 and 1996. Male lambs were castrated at 24 h old. Ewes were introduced to the field for the first time, with their lambs, at 3 days post-partum. Animals were clearly identified by paint-brands ŽSuffolks. or a unique colour code of plastic tape wrapped around their horns ŽBlackfaces. and lambs were marked by paint-brands with their mother’s identification. Marked ewes and lambs grazed together in each field as part of a larger flock of 120 ewes and lambs. Ewes had previously grazed together in 1994 before being separated, by breed, into lambing groups in January 1995, and again in January 1996. Twenty-five Ž9 Suffolk and 16 Blackface. of the ewes recorded in year 1 were also recorded in year 2 when they were raising a lamb of the other breed to year 1. In year 2 one Suffolk lamb in group BS died during the observation period and data from this ewe–lamb pair are omitted from the analysis. Of the 99 lambs recorded 57 were male and 42 female; the ratio of male to female lambs for each group was as follows: BB s 1.78, BS s 1.18, SB s 1.50, SS s 1.08. 2.2. EnÕironments In year 1 ewes and lambs were placed in a 9-ha field ŽField 1, Fig. 1a. that provided fairly uniform grazing and rose approximately 50 m from an altitude of 250 m. In
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year 2, Field 2 was 21.4 ha and composed of distinct lowland and upland regions rising from 250 m to an elevation of 450 m ŽFig. 1b.. In Field 1 the sward was composed predominantly of perennial ryegrass and white clover whereas in Field 2 the grazing contained areas of perennial ryegrass, clover and cocksfoot and a greater diversity of plant species than Field 1. In particular the upland areas contained large areas of Nardus, Agrostis and Festuca species typical of hill grazing. Both fields contained areas of nettle ŽUrtica dioca., spear thistle Ž Cirsium Õulgare . and creeping thistle Ž C. arÕense . throughout the sward. Field 1 was divided into 2 approximately equal-sized areas Žeach 4.5 ha., and Field 2 was divided in 4 areas Žapproximately 5.4 ha each. using obvious landmarks within the fields. Areas 1 and 2 did not differ greatly in Field 1; in Field 2 areas 1 and 2 were in lowland parts of the field and areas 3 and 4 in the upland regions. Field 1 was lined with trees on 2 sides, and had a drinking trough between areas 1 and 2, but otherwise was fairly featureless ŽFig. 1a.. In Field 2 shade was provided by a stand of trees in areas 1 and 2, and by gorse bushes in areas 2 and 3 ŽFig. 1b.. This field also provided more variety with a deep gully running down the length of the field, small rocky outcrops and a public footpath ŽFig. 1b.. 2.3. Data recording Data were collected by scan sampling by an observer who moved through the field using a telescope Ž=8–= 20 magnification. to identify animals without disturbance. Equal numbers of scan samples were carried out in the morning and afternoon with each scan sample taking between 1 ŽField 1. and 2 h ŽField 2. to complete. On average 97.5 " 0.77% of ewes were identified per scan sample, resulting in approximately 50 samples per ewe–lamb dyad. Animals were only recorded if both the ewe and lamb could be identified, and if they remained undisturbed by the presence of the observer. The location Žareas as marked on Fig. 1., nearest neighbour ŽNN. identity and distance were recorded for each marked ewe. The distance between the ewe and her lamb was also recorded. Distance was estimated using known distances between landmarks within the field and taking ewe body length to be approximately 1 m. Ewe associations with their lambs were divided into three categories: close contact Žwithin 5 m.; intermediate Ž5–25 m. and distant Ž30 m or greater, i.e., outside the ewe’s subgroup. to facilitate comparisons with other studies ŽShillito-Walser and Williams, 1986.. In addition, the number and breed of all ewes and lambs within the same subgroup Žwithin a radius of 30 m about the focal ewe. as the ewe were recorded. The use of a fixed distance of 30 m to define a subgroup has been discussed previously ŽLawrence and Wood-Gush, 1988. and is consistent with other studies ŽArnold and Pahl, 1967.. Scan samples were carried out during a 2-month period in both years when lambs were aged between 2 and 4 months old. Fig. 1. Ža. Map of the topographical features and main vegetation or sward types of Field 1. Observation areas are numbered 1 and 2, and delimited by the fencelinces. PRG s perennial ryegrass. Žb. Map of the topographical features and main vegetation or sward types of Field 2. Observation areas numbered 1–4, and delimited by dotted lines. Elevation is given at the top Ž450 m. and bottom Ž250 m..
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Fig. 1 Žcontinued..
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2.4. Statistical analysis There was no significant difference in ewe–lamb behaviour between morning and afternoon scan samples therefore these data were combined before analysis. Data are presented as proportion of total number of scan samples for locations and NN preferences. Effects of ewe and lamb breed, and Field, were investigated using chi-squared tests. There was no evidence for a change in ewe and lamb distance, ewe distance to other ewes, or size of subgroup with time within Field Žby ANOVA.. Mean values for each ewe were calculated first and used in subsequent analysis. The Restricted Maximum Likelihood procedure ŽREML; Patterson and Thompson, 1971. was used as the data were unbalanced. The effects of ewe breed, lamb breed, lamb sex and Field were fitted as fixed Žblock. effects in the model. Ewe identity was fitted as a random variable in between Field comparisons and absorbed to compensate for the fact that some ewes were recorded in both Fields.
3. Results 3.1. Nearest neighbour preferences The mean proportion of scan samples where ewes were seen in closest proximity to each class of neighbour are shown in Table 1. In both Fields and for both breeds of ewe the NN associations differed significantly from random ŽBlackface ewes: x 2 s 16.81, df s 4, P - 0.01; Suffolk ewes: x 2 s 14.95, df s 4, P - 0.01.. Own lamb was the most preferred NN of Blackface ewes, regardless of lamb breed, whereas Suffolk ewes were
Table 1 Nearest Neighbour ŽNN. associations of Blackface and Suffolk ewes in Fields 1 and 2 Class of NN
Ewe Type
Effects
BB
BS
SB
SS
Own lamb Blackface ewe Suffolk ewe Blackface lamb Suffolk lamb
Field 1 0.51 0.32 0.11 0.04 0.03
0.50 0.32 0.10 0.02 0.05
0.44 0.08 0.41 0.02 0.05
0.40 0.11 0.39 0.03 0.07
Ewe breed: P - 0.05 Ewe breed: P - 0.001 Ewe breed: P - 0.001 NS NS
Own lamb Blackface ewe Suffolk ewe Blackface lamb Suffolk lamb
Field 2 0.71 0.18 0.04 0.03 0.05
0.74 0.19 0.01 0.03 0.04
0.47 0.07 0.34 0.05 0.07
0.41 0.04 0.46 0.04 0.06
Ewe breed: P - 0.001 Ewe breed: P - 0.001 Ewe breed: P - 0.001 NS NS
Values are mean proportion of scans where an association of the ewe with a class of NN was observed. Ewe types are as follows: BBs Blackface ewe and lamb; BSs Blackface ewe and Suffolk lamb; SBsSuffolk ewe and Blackface lamb; SSsSuffolk ewe and lamb.
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equally likely to associate with their own lamb or with another Suffolk ewe. Both ewes were more likely to associate with a ewe of the same breed as themselves when their own lamb was not the NN ŽWith same-breed ewe s 88.4%; with other-breed ewe s 11.6% of observations, binomial test z s y12.52, P - 0.001.. Other lambs accounted for less than 10% of associations and there was no preference for lambs that, superficially, resembled the ewe’s own lamb. There were no significant differences between Fields 1 and 2 in associations made by Suffolk ewes. However, in Field 2 Blackface ewes were found closest to their own lamb for significantly more time samples than in Field 1 Ž P - 0.01., accompanied by a decrease in associations with both classes of ewe. Lamb breed had no effect on any of the associations made by the ewes. 3.2. Ewe–lamb associations Mean ewe–lamb distance was significantly affected only by ewe breed Žmean ewe–lamb distance Žm.: BB s 6.23, BS s 5.99, SB s 10.79, SS s 11.89; S.E.M.s 1.17, P - 0.001.. There were no significant effects of breed of lamb, Field or lamb sex. When the scan samples were categorised into close, intermediate and distant associations ŽTable 2. it was evident that Blackface ewes made significantly more close associations with their lambs than Suffolk ewes and significantly fewer distant associations. There was also a significant environment effect with more close associations being made in Field 2 in comparison to Field 1 ŽField 1 s 45.12%, Field 2 s 53.10%, S.E.M.s 2.48, P - 0.01.; and more intermediate associations made in Field 1 relative to Field 2 ŽField 1 s 38.57%, Field 2 s 27.77%, S.E.M.s 1.96, P - 0.001.. There was a small interaction between lamb sex and group with female SS lambs having a higher proportion of close contact observations than male SS lambs Žproportionately 0.54 vs. 0.39 for female and male lambs respectively, S.E.M.s 0.06, P - 0.05.. This relationship was not seen in any other ewe–lamb pairs. 3.3. Ewe distribution and social behaÕiour— Field 1 The distribution of marked ewes of the two breeds within Field 1 was largely overlapping, although there was a tendency for Suffolk ewes to spend less time in area 1
Table 2 Proportion of close, intermediate and distant associations between ewe and lamb expressed as a percentage of the total number of time samples Ewe Type
Close Ž - 5 m. Intermediate Ž5–25 m. Distant Ž G 30 m.
BB
BS
SB
SS
51.26 37.42 10.83
56.17 32.72 10.34
42.25 32.50 23.18
46.76 30.04 25.05
Pooled S.E.M.
Effects
3.50 2.75 3.26
Ewe breed: P - 0.05 NS Ewe breed: P - 0.001
Values are derived from REML analysis of variance. Ewe types as for Table 1.
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and more time in area 2 than Blackface ewes ŽFig. 2; P s 0.1.. Ewes maintained subgroups within the field that consisted predominantly of same-breed ewes ŽTable 3; P - 0.001.. Mean subgroup size for both breeds consisted of approximately equal numbers of ewes and lambs. The size of subgroups, however, was significantly larger for Suffolk ewes ŽTable 3; P - 0.001.. The mean distance between a marked ewe and the nearest ewe to her did not differ between breeds ŽTable 3.. Lamb breed had no effect on ewe distribution within the field, or on ewe relationships with other ewes. 3.4. Ewe distribution and social behaÕiour— Field 2 The distribution of the two breeds of ewe within the larger, more diverse Field 2 clearly differed ŽFig. 2.. Suffolk ewes were recorded in the lowland regions Žareas 1 and 2. in 94.5% of time samples compared to 12.1% of time samples for Blackface ewes Ž x 2 s 36.8, df s 3, P - 0.001.. Although ewes were generally recorded in the same area of the field on most occasions, Suffolk ewes appeared to be more conservative in their choice of environment as 40% of Suffolk ewes were always recorded in the same area of the field in comparison to only 6.9% of Blackface ewes, and 44.8% of Blackface ewes were recorded in 3 or more areas compared to only 16.7% of Suffolks ŽBlackface vs. Suffolk, x 2 s 21.21, df s 2, P - 0.001.. As the distributions of the two breeds were largely non-overlapping the composition of subgroups was almost exclusively of ewes of the same breed ŽTable 3; P - 0.001.. The mean nearest ewe distance for Blackface
Fig. 2. Distribution of Blackface ŽBF. and Suffolk ŽS. ewes between areas 1 and 2 ŽField 1. and areas 1–4 ŽField 2. of the 9 ha Field 1 or the 21 ha Field 2. Significant differences between the breeds are given in the text.
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Field 1
No. ewes in subgroup % BF in subgroup No. lambs in subgroup Nearest ewe distance
Field 2
Effect
BF ewe
S ewe
Pooled S.E.M.
BF ewe
S ewe
Pooled S.E.M.
7.53 66.7 8.30 5.89
9.26 28.0 9.75 5.38
0.29
3.10 81.0 3.81 11.29
11.31 10.3 11.01 4.36
0.37
0.23 0.39
0.26 0.51
Ewe breed: P - 0.001, Field)breed: P - 0.001 Ewe breed: P - 0.001, Field: P - 0.001 Ewe breed: P - 0.001, Field)breed: P - 0.001 BF ewes: Field: P - 0.001
As there were no significant effects of lamb breed on any aspect of ewe association values are means of pooled data from all ewes of the same breed ŽBlackface ŽBF. or Suffolk ŽS...
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Table 3 Effects of ewe breed and Field on ewe associations with other ewes
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ewes increased when compared to Field 1 ŽTable 3; P - 0.001., but was unchanged for Suffolk ewes. There was a significant interaction between environment and ewe breed in average subgroup size as there was a dramatic decline in subgroup size for Blackface ewes in Field 2, but a small increase in mean subgroup size for Suffolk ewes ŽTable 3.. As in Field 1, there was no significant effects of lamb breed on the relationship between its dam and other ewes.
4. Discussion In the present study the nature of the relationship between the ewe and her lamb appears to be a function of ewe breed and behaviour, regardless of the physical environment, whereas the relationship between the ewe and other non-related sheep appears to be affected both by breed and environment. The breed or behaviour of the lamb had no effect on the behaviour of the ewe. Surprisingly, lamb sex also had very little effect on the ewe–lamb relationship. Previous studies have suggested that male lambs tend to be further from the ewe than female lambs ŽGrubb and Jewell, 1966; Shillito-Walser and Williams, 1986., perhaps leading up to the dissociation of male lambs from the matrilineal group ŽHunter and Milner, 1963; Arnold and Pahl, 1974.. It may be that the lambs used in the present study were too young to begin the process of natural weaning and sexual segregation. Although the lambs were the same age as the twin lambs used by Shillito-Walser and Williams Ž1986., they were all singletons which tend to be weaned at a later age than twins ŽPrice et al., 1984.. The differential attachment of male and female lambs was evident only in the Suffolk ewe with Suffolk lamb group ŽSS.. Whether this group is more likely to wean their lambs earlier than other groups is not known. Alternatively, the castration of male lambs may have abolished any sex differences in ewe–lamb association. The non-random nature of ewe associations is consistent with other observations ŽArnold and Pahl, 1974; Arnold et al., 1981.. Segregation of the two ewe breeds was clearly demonstrated in both environments. Several studies have shown that, although same-breed groups integrate within 3 weeks ŽArnold and Pahl, 1974., flocks composed of different breeds remain permanently separate ŽWinfield and Mullaney, 1973; Arnold and Pahl, 1974; Shillito-Walser and Hague, 1981.. The present study suggests that no significant breed integration occurs during 4 months of contact although some individual animals were observed to form long-term associations with ewes of the other breed ŽC. Dwyer, unpublished observation.. Sheep appear to recognise individual animals by both visual ŽKendrick et al., 1995. and olfactory cues ŽArnold, 1985., with group identity possibly being maintained predominantly by odour. A breed identity seems to be established by using mainly visual cues and probably develops by lambs learning to recognise the appearance of their mothers ŽShillito-Walser, 1980.. This suggests that, whilst integration of same-breed groups occurs with time, as odour cues change, integration of different breed groups will not occur. This hypothesis would predict that the embryo transfer lambs used in the present study will have the breed identity of their mothers, regardless of their own breed.
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The ewe’s own lamb was the most frequent nearest neighbour, with other lambs either being actively avoided by the ewe or simply not encountered as they tended to remain close to their own mothers. The ewe–lamb relationship appeared to be dictated by the behaviour of the ewe with lamb breed having no significant effect on the mean distance between the ewe and lamb. Ewes maintain close spatial relationships with their lambs in the first week after birth ŽMcBride et al., 1967; Morgan and Arnold, 1974; O’Connor, 1990. when the ewe is attentive to the location of her lamb, approaching the lamb very frequently ŽHinch et al., 1987; O’Connor, 1990.. Thereafter the distance between ewe and lamb increases to a plateau by 28–36 days after birth ŽMorgan and Arnold, 1974; O’Connor, 1990., until at least 100 days after birth ŽArnold et al., 1979.. Analysis of ewe and lamb behaviour suggests that the lamb is responsible for more than 80% of approaches and contacts between the pair from week 6 ŽO’Connor, 1990.. The ewe, however, controls the dynamics of the relationship and, as can be seen in the present study, is ultimately responsible for the distance between the ewe and lamb because lambs of different breeds are the same distance from the ewe. The reason why Blackface ewes should maintain closer spatial relationships to their lambs than Suffolk ewes is intriguing. Blackface ewes are known to spend more time grooming and vocalising to their neonatal lambs than Suffolk ewes ŽDwyer and Lawrence, 1998; Dwyer et al., 1998. and may, therefore, have formed a stronger bond with their lamb. In addition to full approaches to their mother, lambs are alert to the behaviour of their mother and make increasing numbers of partial approaches whenever the ewe raises her head ŽO’Connor, 1990.. Blackface-raised lambs were observed to be within 5 m of their mothers on significantly more occasions than Suffolk-raised lambs, suggesting that they more frequently approached their mothers or, having approached, remained with their mothers for longer. This may indicate a higher frequency of ‘head-up’ postures Žthe posture used by the ewe to indicate that the lamb may approach. by the Blackface ewes, although whether this represents a generally greater alertness in Blackface ewes compared to Suffolks or a greater awareness of their lamb is not clear. The general trends in social behaviour between the two breeds are in line with previous observations, that is small subgroup size in the hill breeds and larger subgroups in lowland breeds Že.g., Clun Forest. or no subgrouping in Merinos ŽArnold and Pahl, 1967; Arnold et al., 1981; Shillito-Walser and Hague, 1981.. Furthermore, a closer association within some breeds than others has also been reported in other breeds ŽMerino vs. Wiltshire Horn: Winfield and Mullaney, 1973.. The finding that ewes altered their social behaviour depending on their environment, however, has not been reported before. In Field 2 the subgroup sizes of Blackface ewes were similar to those previously seen in Blackface ewes on an established home range ŽLawrence and Wood-Gush, 1988.. It may be, therefore, that either the size of the field, availability of grass types or the relative lack of topographical features in Field 1 constrained the breed-specific social behaviour of the Blackface such that they made closer associations with other ewes and formed larger subgroups. The Suffolk ewes always formed closer associations with other ewes than Blackfaces and aggregated into a small number of larger subgroups. Surprisingly, however, when placed in the larger field the distance between Suffolk ewes remained the same but subgroup sizes increased further. This clearly demonstrated that the social behaviour of the sheep was not simply a function of
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the available space but suggests that other factors affect the relationships between animals. In Rocky Mountain Bighorn sheep 65% of the variance in spatial distribution of animals was accounted for by environmental variables such as slope, palatability of grasses, elevation and nitrogen content of vegetation ŽShannon et al., 1975.. The selection of a suitable home range by individual animals in a new environment may partly explain both the distribution of animals and the increase in subgroup size for Suffolks in Field 2 compared to Field 1. It seems likely, however, that social relationships between animals also dictate where they establish their home range. Hunter and Davies Ž1963. demonstrated that returning lambs to an already occupied field led to the establishment of new home ranges on underoccupied areas by the incomers that may have been on less favoured areas of the field. Thus it may be that social constraints may prevent animals from making maximal usage of the available vegetation. The differences between the two breeds in their social relationships may be related to physical factors, such as activity patterns, dietary preferences or to some intrinsic breed-specific gregariousness. The present paper has already demonstrated that Blackface ewes form closer relationships to their lambs than Suffolk ewes. Furthermore, it is known that maternal ewes do not react to isolation from adult conspecifics in the presence of their own lamb ŽPoindron et al., 1994.. The closer bond between ewe and lamb in the Blackface may be indicative of a weaker attachment to the flock, at least during the summer months, such that Blackface ewes maintain larger spatial relationships with other ewes than Suffolks. The Merino is more strongly attached to the flock than other breeds and more weakly to their own lamb ŽMcBride et al., 1967.. The Suffolk may represent a point somewhere between the Merino and hill breeds such as the Blackface. Some Blackface ewes were frequently observed to be more than 30 m from any other ewe, with their lamb, and were apparently acting as an individual animal rather than a flock member ŽC. Dwyer, unpublished observation.. Grubb and Jewell Ž1966. suggest that in feral Soay sheep the flocking instinct is not strong and Soays tend to act as individuals when alarmed. They suggest that increasing domestication has produced animals that are tolerant to crowding. Thus selection for production characteristics may have indirectly selected for animals, such as the Suffolk, that are more gregarious. Although ewes adopted largely overlapping distributions in Field 1, when given access to a larger and more diverse environment in Field 2 the two breeds used mostly separate areas of the field. Blackface ewes used predominantly the upland areas of the field and appeared to range over a larger area than Suffolks who confined themselves to a relatively small area in the lowland part of the field. It is possible that the preferred qualities of a home range for Blackface ewes were abundant in Field 2 but restricted to a small area for Suffolk ewes. The ewes used in this study were obtained as 1-year olds from typical hill ŽBlackface. and lowland ŽSuffolk. farms. Their early grazing experiences may have conditioned them to certain grass types and features of their environment which then influenced their preferred home range in novel fields. The distribution of Suffolk ewes in this study appears to follow the distribution of the best swards of perennial ryegrass and clover in both fields. The Blackface ewes, however, despite grazing the perennial ryegrass sward in Field 1, seemed to prefer the poorer hill grazing of Agrostis, Festuca and Nardus species in Field 2. A cross-fostering study of Welsh
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and Clun Forest ewes and lambs ŽKey and MacIver, 1980. suggested that preferences of lambs for upland grazing, and their dispersal patterns, may be related to their mothers breed and, hence their early life experience. In addition, dietary preferences are known to affect foraging location of lambs ŽScott et al., 1995. in the absence of social preferences. Our ewes, however, were only able to express their preferences in Field 2 when the diverse nature of the grass types and topography provided both a hill and a lowland type location. The greater dispersal of the Blackface ewes in Field 2 may also have been a function of their choice of foraging area as the upland region may have required greater ranging behaviour to obtain a similar nutritional intake. The location and home range behaviour of the embryo transferred lambs in the present study would be expected, if early life experience determined social preferences, to conform to those of their mothers breed rather than their own breed. In conclusion, this study has demonstrated that the social organization and dispersal of ewes varies according to breed. Furthermore, the nature of their social behaviour and subgrouping can be modified by environment although the direction of change differed between breeds. These results clearly demonstrate that social organization is more complex than a simple function of available space. Blackface ewes were significantly less gregarious than Suffolk ewes which may be related to the relative domestication, or husbandry, of the two breeds. It is possible, however, that early life experience may have dictated the subsequent foraging choices made by ewes and that these affected social associations indirectly through greater dispersal and ranging of ewes eating less nutritious plant species. Further studies on the social behaviour of the embryo-transfer lambs used in this study may help to distinguish between the effects of experience and intrinsic differences between breeds. The relationship of the ewe to her lamb was more resistant to environmental influence than her relationship to other adult ewes. Blackface ewes maintain closer spatial contact with their lambs than Suffolk ewes which may be related to closer associations being formed immediately after birth. The flexibility in the social relationships formed by sheep may have adaptive significance for the movement of animals into new environments.
Acknowledgements The authors would like to thank the following: Jack FitzSimons and Mark Ramsay for animal husbandry, Hazel Brown for assistance with observations in Year 1, Sandy Clelland for providing the botanical analysis of the fields; John Boyd for his assistance with the maps of the fields, and Edinburgh Genetics for performing the embryo-transfer procedures. This study was supported by the Scottish Office Agriculture, Environment and Fisheries Department.
References Arnold, G.W., 1985. Associations and social behaviour. In: Fraser, A.F. ŽEd.., Ethology of Farm Animals, Elsevier, Amsterdam, pp. 233–248.
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Arnold, G.W., Pahl, P.J., 1967. Sub-grouping in sheep flocks. Proc. Ecol. Soc. Aust. 2, 183–189. Arnold, G.W., Pahl, P.J., 1974. Some aspects of social behaviour in domestic sheep. Anim. Behav. 22, 592–600. Arnold, G.W., Wallace, S.R., Maller, R.A., 1979. Some factors affecting involved in the natural weaning processes of sheep. Appl. Anim. Ethol. 5, 43–50. Arnold, G.W., Wallace, S.R., Rea, W.A., 1981. Associations between individuals and home-range behaviour in natural flocks of three breeds of domestic sheep. Appl. Anim. Ethol. 7, 239–257. Berger, J., 1979. Social ontogeny and behavioural diversity: consequences for Bighorn sheep OÕis canadensis inhabiting desert and mountain environments. J. Zool., Lond. 188, 251–266. Dwyer, C.M., Lawrence, A.B., Brown, H.E., Simm, G., 1996. Effect of ewe and lamb genotype on gestation length, lambing ease, and neonatal behaviour of lambs. Reprod. Fertil. Devel. 8, 1123–1129. Dwyer, C.M., Lawrence, A.B., 1997. Social relationships between ewes of two breeds. In: Forbes, J.M., Lawrence, T.L.J., Rodway, R.G., Varley, M.A. ŽEds.., Animal Choices, Occasional Publications of the BSAS, No. 20, pp. 92–93. Dwyer, C.M., Lawrence, A.B., 1998. Variability in the in expression of maternal behaviour in primiparous sheep: Effects of genotype and litter size. Appl. Anim. Behav. Sci. 58, 311–330. Dwyer, C.M., McLean, K.A., Deans, L.A., Chirnside, J., Calvert, S.K., Lawrence, A.B., 1998. Vocalisations between mother and young in the sheep: Effects of breed and maternal experience. Appl. Anim. Behav. Sci., 58, 105–119. Grubb, P., Jewell, P.A., 1966. Social group and home range in feral Soay sheep. Symposia Zool. Soc., Lond. 18, 179–210. Hinch, G.N., Lecrivain, E., Lynch, J.J., Elwin, R.L., 1987. Changes in maternal-young associations with increasing age of lambs. Appl. Anim. Behav. Sci. 17, 305–318. Hunter, R.F., Davies, G.E., 1963. The effect of method of rearing on the social behaviour of Scottish Blackface hoggets. Anim. Prod. 5, 183–194. Hunter, R.F., Milner, C., 1963. The behaviour of individual, related and groups of South Country Cheviot hill sheep. Anim. Behav. 11, 507–513. Kendrick, K.M., Atkins, K., Hinton, M.R., Broad, K.D., Fabre-Nys, C., Keverne, B., 1995. Facial and vocal discrimination in sheep. Anim. Behav. 49, 1665–1676. Key, C., MacIver, R.M., 1980. The effects of maternal influences on sheep: breed differences in grazing, resting and courtship behaviour. Appl. Anim. Ethol. 6, 33–48. Kilgour, R., 1972. Behaviour of sheep at lambing. NZ J. Agric. 125, 24–27. Lawrence, A.B., Wood-Gush, D.G.M., 1988. Home-range behaviour and social organization of Scottish Blackface sheep. J. Appl. Ecol. 25, 25–40. Le Pendu, Y., Maublanc, M.-L., Briedermann, L., Dubois, M., 1996. Spatial structure and activity in groups of Mediterranean Mouflon Ž OÕis gmelini .: a comparative study. Appl. Anim. Behav. Sci. 46, 201–216. Lynch, J.J., 1967. Ranging behaviour of sheep in large areas. Proc. Ecol. Soc. Aust. 2, 167–169. Lynch, J.J., Hinch, G.N., Adams, D.B., 1992. The behaviour of sheep: biological principles and implications for production. C.A.B. International, Oxon, UK and CSIRO Publications, Melbourne, Australia, pp. 48–95. Maisels, F.G., 1993. Seasonal variation in grouping patterns of the forest-dwelling Cyprus Mouflon, OÕis orientalis. J. Zool., Lond. 229, 527–532. McBride, G., Arnold, G.W., Alexander, G., Lynch, J.J., 1967. Ecological aspects of the behaviour of domestic animals. Proc. Ecol. Soc. Aust. 2, 133–165. McKelvey, W.A.C., Robinson, J.J., Aitkin, R.P., 1985b. A simplified technique for the transfer of ovine embryos by laparoscopy. Vet. Record 117, 492–494. McKelvey, W.A.C., Robinson, J.J., Aitkin, R.P., Henderson, G.D., 1985a. The evaluation of a laparoscopic technique in ewes. Theriogenol. 24, 519–535. Morgan, P.D., Arnold, G.W., 1974. Behavioural relationships between Merino ewes and lambs during the four weeks after birth. Anim. Prod. 19, 169–176. O’Connor, C.E., 1990. Mother-offspring relationships in Scottish Blackface sheep. PhD. Thesis, University of Edinburgh. Patterson, H.D., Thompson, R., 1971. Recovery of inter-block information when block sizes are unequal. Biometrika 58, 545–554.
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Poindron, P., Caba, M., Gomora Arrati, P., Krehbiel, D., Beyer, C., 1994. Responses of maternal and non-maternal ewes to social and mother–young separation. Behav. Process. 31, 97–110. Price, E.O., Martinez, C.L., Coe, B.L., 1984. The effects of twinning on mother–offspring behaviour in range beef cattle. Appl. Anim. Behav. Sci. 13, 309–320. Scott, C.B., Provenza, F.D., Banner, R.E., 1995. Dietary habits and social interactions affect choice of feeding location by sheep. Appl. Anim. Behav. Sci. 45, 225–237. Shannon, N.H., Hudson, R.J., Brink, V.C., Kitts, W.D., 1975. Determinants of spatial distribution of Rocky Mountain Bighorn sheep. J. Wildlife Manage. 39, 387–401. Shillito-Walser, E., 1980. Maternal recognition and breed identity in lambs living in a mixed flock of Jacob, Clun Forest, and Dalesbred sheep. Appl. Anim. Ethol. 6, 221–231. Shillito-Walser, E., Hague, P., 1981. Field observations on a flock of ewes and lambs made up of Clun Forest, Dalesbred and Jacob sheep. Appl. Anim. Ethol. 7, 175–178. Shillito-Walser, E., Williams, T., 1986. Pair-association in twin lambs before and after weaning. Appl. Anim. Behav. Sci. 15, 241–245. Stolba, A., Hinch, G.N., Lynch, J.J., Adams, D.B., Munro, R.K., Davies, H.I., 1990. Social organisation of Merino sheep of different ages, sex and family structure. Appl. Anim. Behav. Sci. 27, 337–349. Winfield, C.G., Mullaney, P.D., 1973. A note on the social behaviour of a flock of Merino and Wiltshire Horn sheep. Anim. Prod. 17, 93–95.
Ewe–ewe and ewe–lamb behaviour in a hill and a lowland breed of sheep: a study using embryo transfer C.M. Dwyer ) , A.B. Lawrence BehaÕioural Sciences Department, Animal Biology DiÕision, SAC, King’s Buildings, West Mains Road, Edinburgh, EH9 3JG, UK Accepted 20 July 1998
Abstract Domestic sheep have a strong social tendency. The nature of this gregariousness, however, varies with season, breed, sex and age. In this study the social behaviour of two breeds of ewe ŽSuffolk and Scottish Blackface. was investigated over two years in two different environments. In addition, to examine whether lamb behaviour would affect the behaviour of the ewe, an embryo transfer study was carried out between the two breeds resulting in four combinations of ewe and lamb ŽBlackface ewe with Blackface lamb, n s 25; Blackface ewe with Suffolk lamb, n s 24; Suffolk ewe with Suffolk lamb, n s 25; Suffolk ewe with Suffolk lamb, n s 25.. All ewes and lambs grazed together in Field 1 Žyear 1. and Field 2 Žyear 2.. Field 1 was 9 ha and rather uniform; Field 2 was 21.4 ha and had two distinct regions: an upland and a lowland area. Blackface ewes preferentially associated with their own lamb whereas Suffolk ewes associated equally with their own lamb or another Suffolk ewe, there was no effect of lamb breed Žpercent observations with own lamb as nearest neighbour, Field 1: Blackface ewes s 50.2%, Suffolk ewes s 43.5%, P - 0.05; Field 2: Blackface ewes s 73.1%, Suffolk ewes s 43.5%, P - 0.001.. Blackface ewes were also significantly closer to their lambs than Suffolk ewes, regardless of year or lamb breed ŽBlackface ewes s 6.10 m, Suffolk ewes s 11.54 m, P - 0.001.. When own lamb was not the nearest neighbour ewes associated with other ewes of the same breed as themselves ŽWith same-breed ewe s 88.4% of observations, with other-breed ewe s 11.6%, P - 0.001.. In Field 1 the distribution of both breeds in the field was similar to one another but ewes maintained subgroups composed predominantly of their own breed Ž P - 0.001.. The mean distance between ewes was the same for both breeds, however subgroups were significantly smaller for Blackface ewes Ž7.53 and 9.26 ewes for Blackface and Suffolk respectively, P - 0.001.. In Field 2
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Corresponding author. Tel.: q44-131-535-3200; fax: q44-131-535-3121; e-mail: [email protected]
0168-1591r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 1 5 9 1 Ž 9 8 . 0 0 2 0 3 - 2
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Blackface ewes were found mainly in the upland region of the field whereas Suffolk ewes were almost exclusively in the lowland areas. Mean distance between ewes increased markedly for Blackface ewes when compared to ewe–ewe distance in Field 1 but was unchanged for Suffolks Ž11.29 vs. 4.36 m for Blackface and Suffolk ewes respectively, P - 0.001.. Subgroup size also declined for Blackface ewes in comparison to Field 1 but increased for Suffolks ŽBlackfaces 3.10, Suffolks 11.31 ewes, P - 0.001.. Lamb breed had no effect on the social behaviour of either breed of ewe. The two breeds had differing behaviour in their relationship to their own lamb. Their relationship to other ewes, however, was significantly modified by the environment although the Blackface breed was less gregarious than the Suffolk under both conditions. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Sheep; Social behaviour; Spatial associations; Breed; Influence
1. Introduction Domestic sheep exhibit strong flocking behaviour, and maintain close spatial and social contacts with other sheep ŽLynch et al., 1992.. However, the nature of these contacts does not appear to be rigid. The social behaviour of both wild and domestic sheep varies seasonally. For example a mixed-age flock of Scottish Blackface ewes occupied a larger home range during the summer months than in the winter ŽLawrence and Wood-Gush, 1988., and social group size changed in the summer in Cyprus Mouflon ŽMaisels, 1993.. The age, sex and composition of the flock also affect the expression of social behaviour in both wild, feral and domestic sheep Že.g., Soay: Grubb and Jewell, 1966; Merino: Arnold and Pahl, 1974; Stolba et al., 1990; Mouflon: Le Pendu et al., 1996.. In addition, several authors report breed differences in the closeness and variety of social contact with, for example, Merino sheep forming close associations in contrast to the sub-grouping seen in other breeds ŽWinfield and Mullaney, 1973; Arnold et al., 1981; Shillito-Walser and Hague, 1981.. The environment in which sheep are placed can also have an effect on social behaviour ŽMcBride et al., 1967., with a greater degree of alertness shown in barren environments by Merinos ŽStolba et al., 1990. and a change in the frequency of some behaviours, especially play, between mountain and desert-living Bighorn sheep ŽBerger, 1979.. In the present study the social relationships of two breeds of sheep were investigated whilst grazing with lambs at foot: a lowland breed ŽSuffolk. and a hill breed ŽScottish Blackface.. The effect of environment on the nature of their social behaviour was examined as previous studies suggest that a more diverse environment may encourage the expression of greater variability in social behaviour ŽLynch, 1967; Stolba et al., 1990.. Reported differences in the social behaviour of hill and intensively husbanded sheep ŽWinfield and Mullaney, 1973; Arnold et al., 1981; Shillito-Walser and Hague, 1981. may be partly attributable to the field types encountered by the breeds under normal husbandry conditions. The behaviour of the lambs of the two breeds of sheep has already been shown to differ in the neonatal period ŽDwyer et al., 1996.. As these differences may persist and the behaviour of the young may affect the behaviour of the ewe, as has been suggested for ewes raising cross-fostered goat kids ŽKilgour, 1972., an
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embryo transfer study was also carried out between the two breeds to distinguish between maternal and lamb effects on social behaviour. Thus the effects of ewe breed, lamb breed and environmental diversity on the expression of social behaviour in ewes were investigated. A preliminary report of some of these results has already been published ŽDwyer and Lawrence, 1997..
2. Materials and methods 2.1. Animals Ewes were of a hill ŽScottish Blackface. or a lowland ŽSuffolk. breed and were aged 3 Žyears 1 and 2. or 4 years Žyear 2 only.. Ewes had previously been obtained from a number of different flocks as 1-year-olds. All ewes were multiparous and in their second or third parity. In year 1 40 animals were used Ž20 each of Suffolk and Blackface.; in year 2 60 animals were observed Ž30 of each breed.. Ewes were given single embryos by embryo transfer in both years. Donor ewes were super-ovulated, by injection of ovine FSH ŽOvagen, Immuno-Chemical Products, Auckland, NZ., and inseminated by laparoscopic artificial insemination with fresh semen using the technique described by McKelvey et al. Ž1985a.. Embryos were recovered on day 6 following insemination and transferred laparoscopically to synchronised recipient ewes, using the procedure of McKelvey et al. Ž1985b.. Embryos were transferred across breeds such that equal numbers of the possible breed combinations were obtained: Blackface ewes with Blackface lambs ŽBB, total n s 25., Blackface ewes with Suffolk lambs ŽBS, n s 25., Suffolk ewes with Suffolk lambs ŽSS, n s 25., and Suffolk ewes with Blackface lambs ŽSB, n s 25.. Ewes lambed indoors in April 1995 and 1996. Male lambs were castrated at 24 h old. Ewes were introduced to the field for the first time, with their lambs, at 3 days post-partum. Animals were clearly identified by paint-brands ŽSuffolks. or a unique colour code of plastic tape wrapped around their horns ŽBlackfaces. and lambs were marked by paint-brands with their mother’s identification. Marked ewes and lambs grazed together in each field as part of a larger flock of 120 ewes and lambs. Ewes had previously grazed together in 1994 before being separated, by breed, into lambing groups in January 1995, and again in January 1996. Twenty-five Ž9 Suffolk and 16 Blackface. of the ewes recorded in year 1 were also recorded in year 2 when they were raising a lamb of the other breed to year 1. In year 2 one Suffolk lamb in group BS died during the observation period and data from this ewe–lamb pair are omitted from the analysis. Of the 99 lambs recorded 57 were male and 42 female; the ratio of male to female lambs for each group was as follows: BB s 1.78, BS s 1.18, SB s 1.50, SS s 1.08. 2.2. EnÕironments In year 1 ewes and lambs were placed in a 9-ha field ŽField 1, Fig. 1a. that provided fairly uniform grazing and rose approximately 50 m from an altitude of 250 m. In
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year 2, Field 2 was 21.4 ha and composed of distinct lowland and upland regions rising from 250 m to an elevation of 450 m ŽFig. 1b.. In Field 1 the sward was composed predominantly of perennial ryegrass and white clover whereas in Field 2 the grazing contained areas of perennial ryegrass, clover and cocksfoot and a greater diversity of plant species than Field 1. In particular the upland areas contained large areas of Nardus, Agrostis and Festuca species typical of hill grazing. Both fields contained areas of nettle ŽUrtica dioca., spear thistle Ž Cirsium Õulgare . and creeping thistle Ž C. arÕense . throughout the sward. Field 1 was divided into 2 approximately equal-sized areas Žeach 4.5 ha., and Field 2 was divided in 4 areas Žapproximately 5.4 ha each. using obvious landmarks within the fields. Areas 1 and 2 did not differ greatly in Field 1; in Field 2 areas 1 and 2 were in lowland parts of the field and areas 3 and 4 in the upland regions. Field 1 was lined with trees on 2 sides, and had a drinking trough between areas 1 and 2, but otherwise was fairly featureless ŽFig. 1a.. In Field 2 shade was provided by a stand of trees in areas 1 and 2, and by gorse bushes in areas 2 and 3 ŽFig. 1b.. This field also provided more variety with a deep gully running down the length of the field, small rocky outcrops and a public footpath ŽFig. 1b.. 2.3. Data recording Data were collected by scan sampling by an observer who moved through the field using a telescope Ž=8–= 20 magnification. to identify animals without disturbance. Equal numbers of scan samples were carried out in the morning and afternoon with each scan sample taking between 1 ŽField 1. and 2 h ŽField 2. to complete. On average 97.5 " 0.77% of ewes were identified per scan sample, resulting in approximately 50 samples per ewe–lamb dyad. Animals were only recorded if both the ewe and lamb could be identified, and if they remained undisturbed by the presence of the observer. The location Žareas as marked on Fig. 1., nearest neighbour ŽNN. identity and distance were recorded for each marked ewe. The distance between the ewe and her lamb was also recorded. Distance was estimated using known distances between landmarks within the field and taking ewe body length to be approximately 1 m. Ewe associations with their lambs were divided into three categories: close contact Žwithin 5 m.; intermediate Ž5–25 m. and distant Ž30 m or greater, i.e., outside the ewe’s subgroup. to facilitate comparisons with other studies ŽShillito-Walser and Williams, 1986.. In addition, the number and breed of all ewes and lambs within the same subgroup Žwithin a radius of 30 m about the focal ewe. as the ewe were recorded. The use of a fixed distance of 30 m to define a subgroup has been discussed previously ŽLawrence and Wood-Gush, 1988. and is consistent with other studies ŽArnold and Pahl, 1967.. Scan samples were carried out during a 2-month period in both years when lambs were aged between 2 and 4 months old. Fig. 1. Ža. Map of the topographical features and main vegetation or sward types of Field 1. Observation areas are numbered 1 and 2, and delimited by the fencelinces. PRG s perennial ryegrass. Žb. Map of the topographical features and main vegetation or sward types of Field 2. Observation areas numbered 1–4, and delimited by dotted lines. Elevation is given at the top Ž450 m. and bottom Ž250 m..
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Fig. 1 Žcontinued..
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2.4. Statistical analysis There was no significant difference in ewe–lamb behaviour between morning and afternoon scan samples therefore these data were combined before analysis. Data are presented as proportion of total number of scan samples for locations and NN preferences. Effects of ewe and lamb breed, and Field, were investigated using chi-squared tests. There was no evidence for a change in ewe and lamb distance, ewe distance to other ewes, or size of subgroup with time within Field Žby ANOVA.. Mean values for each ewe were calculated first and used in subsequent analysis. The Restricted Maximum Likelihood procedure ŽREML; Patterson and Thompson, 1971. was used as the data were unbalanced. The effects of ewe breed, lamb breed, lamb sex and Field were fitted as fixed Žblock. effects in the model. Ewe identity was fitted as a random variable in between Field comparisons and absorbed to compensate for the fact that some ewes were recorded in both Fields.
3. Results 3.1. Nearest neighbour preferences The mean proportion of scan samples where ewes were seen in closest proximity to each class of neighbour are shown in Table 1. In both Fields and for both breeds of ewe the NN associations differed significantly from random ŽBlackface ewes: x 2 s 16.81, df s 4, P - 0.01; Suffolk ewes: x 2 s 14.95, df s 4, P - 0.01.. Own lamb was the most preferred NN of Blackface ewes, regardless of lamb breed, whereas Suffolk ewes were
Table 1 Nearest Neighbour ŽNN. associations of Blackface and Suffolk ewes in Fields 1 and 2 Class of NN
Ewe Type
Effects
BB
BS
SB
SS
Own lamb Blackface ewe Suffolk ewe Blackface lamb Suffolk lamb
Field 1 0.51 0.32 0.11 0.04 0.03
0.50 0.32 0.10 0.02 0.05
0.44 0.08 0.41 0.02 0.05
0.40 0.11 0.39 0.03 0.07
Ewe breed: P - 0.05 Ewe breed: P - 0.001 Ewe breed: P - 0.001 NS NS
Own lamb Blackface ewe Suffolk ewe Blackface lamb Suffolk lamb
Field 2 0.71 0.18 0.04 0.03 0.05
0.74 0.19 0.01 0.03 0.04
0.47 0.07 0.34 0.05 0.07
0.41 0.04 0.46 0.04 0.06
Ewe breed: P - 0.001 Ewe breed: P - 0.001 Ewe breed: P - 0.001 NS NS
Values are mean proportion of scans where an association of the ewe with a class of NN was observed. Ewe types are as follows: BBs Blackface ewe and lamb; BSs Blackface ewe and Suffolk lamb; SBsSuffolk ewe and Blackface lamb; SSsSuffolk ewe and lamb.
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equally likely to associate with their own lamb or with another Suffolk ewe. Both ewes were more likely to associate with a ewe of the same breed as themselves when their own lamb was not the NN ŽWith same-breed ewe s 88.4%; with other-breed ewe s 11.6% of observations, binomial test z s y12.52, P - 0.001.. Other lambs accounted for less than 10% of associations and there was no preference for lambs that, superficially, resembled the ewe’s own lamb. There were no significant differences between Fields 1 and 2 in associations made by Suffolk ewes. However, in Field 2 Blackface ewes were found closest to their own lamb for significantly more time samples than in Field 1 Ž P - 0.01., accompanied by a decrease in associations with both classes of ewe. Lamb breed had no effect on any of the associations made by the ewes. 3.2. Ewe–lamb associations Mean ewe–lamb distance was significantly affected only by ewe breed Žmean ewe–lamb distance Žm.: BB s 6.23, BS s 5.99, SB s 10.79, SS s 11.89; S.E.M.s 1.17, P - 0.001.. There were no significant effects of breed of lamb, Field or lamb sex. When the scan samples were categorised into close, intermediate and distant associations ŽTable 2. it was evident that Blackface ewes made significantly more close associations with their lambs than Suffolk ewes and significantly fewer distant associations. There was also a significant environment effect with more close associations being made in Field 2 in comparison to Field 1 ŽField 1 s 45.12%, Field 2 s 53.10%, S.E.M.s 2.48, P - 0.01.; and more intermediate associations made in Field 1 relative to Field 2 ŽField 1 s 38.57%, Field 2 s 27.77%, S.E.M.s 1.96, P - 0.001.. There was a small interaction between lamb sex and group with female SS lambs having a higher proportion of close contact observations than male SS lambs Žproportionately 0.54 vs. 0.39 for female and male lambs respectively, S.E.M.s 0.06, P - 0.05.. This relationship was not seen in any other ewe–lamb pairs. 3.3. Ewe distribution and social behaÕiour— Field 1 The distribution of marked ewes of the two breeds within Field 1 was largely overlapping, although there was a tendency for Suffolk ewes to spend less time in area 1
Table 2 Proportion of close, intermediate and distant associations between ewe and lamb expressed as a percentage of the total number of time samples Ewe Type
Close Ž - 5 m. Intermediate Ž5–25 m. Distant Ž G 30 m.
BB
BS
SB
SS
51.26 37.42 10.83
56.17 32.72 10.34
42.25 32.50 23.18
46.76 30.04 25.05
Pooled S.E.M.
Effects
3.50 2.75 3.26
Ewe breed: P - 0.05 NS Ewe breed: P - 0.001
Values are derived from REML analysis of variance. Ewe types as for Table 1.
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and more time in area 2 than Blackface ewes ŽFig. 2; P s 0.1.. Ewes maintained subgroups within the field that consisted predominantly of same-breed ewes ŽTable 3; P - 0.001.. Mean subgroup size for both breeds consisted of approximately equal numbers of ewes and lambs. The size of subgroups, however, was significantly larger for Suffolk ewes ŽTable 3; P - 0.001.. The mean distance between a marked ewe and the nearest ewe to her did not differ between breeds ŽTable 3.. Lamb breed had no effect on ewe distribution within the field, or on ewe relationships with other ewes. 3.4. Ewe distribution and social behaÕiour— Field 2 The distribution of the two breeds of ewe within the larger, more diverse Field 2 clearly differed ŽFig. 2.. Suffolk ewes were recorded in the lowland regions Žareas 1 and 2. in 94.5% of time samples compared to 12.1% of time samples for Blackface ewes Ž x 2 s 36.8, df s 3, P - 0.001.. Although ewes were generally recorded in the same area of the field on most occasions, Suffolk ewes appeared to be more conservative in their choice of environment as 40% of Suffolk ewes were always recorded in the same area of the field in comparison to only 6.9% of Blackface ewes, and 44.8% of Blackface ewes were recorded in 3 or more areas compared to only 16.7% of Suffolks ŽBlackface vs. Suffolk, x 2 s 21.21, df s 2, P - 0.001.. As the distributions of the two breeds were largely non-overlapping the composition of subgroups was almost exclusively of ewes of the same breed ŽTable 3; P - 0.001.. The mean nearest ewe distance for Blackface
Fig. 2. Distribution of Blackface ŽBF. and Suffolk ŽS. ewes between areas 1 and 2 ŽField 1. and areas 1–4 ŽField 2. of the 9 ha Field 1 or the 21 ha Field 2. Significant differences between the breeds are given in the text.
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Field 1
No. ewes in subgroup % BF in subgroup No. lambs in subgroup Nearest ewe distance
Field 2
Effect
BF ewe
S ewe
Pooled S.E.M.
BF ewe
S ewe
Pooled S.E.M.
7.53 66.7 8.30 5.89
9.26 28.0 9.75 5.38
0.29
3.10 81.0 3.81 11.29
11.31 10.3 11.01 4.36
0.37
0.23 0.39
0.26 0.51
Ewe breed: P - 0.001, Field)breed: P - 0.001 Ewe breed: P - 0.001, Field: P - 0.001 Ewe breed: P - 0.001, Field)breed: P - 0.001 BF ewes: Field: P - 0.001
As there were no significant effects of lamb breed on any aspect of ewe association values are means of pooled data from all ewes of the same breed ŽBlackface ŽBF. or Suffolk ŽS...
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Table 3 Effects of ewe breed and Field on ewe associations with other ewes
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ewes increased when compared to Field 1 ŽTable 3; P - 0.001., but was unchanged for Suffolk ewes. There was a significant interaction between environment and ewe breed in average subgroup size as there was a dramatic decline in subgroup size for Blackface ewes in Field 2, but a small increase in mean subgroup size for Suffolk ewes ŽTable 3.. As in Field 1, there was no significant effects of lamb breed on the relationship between its dam and other ewes.
4. Discussion In the present study the nature of the relationship between the ewe and her lamb appears to be a function of ewe breed and behaviour, regardless of the physical environment, whereas the relationship between the ewe and other non-related sheep appears to be affected both by breed and environment. The breed or behaviour of the lamb had no effect on the behaviour of the ewe. Surprisingly, lamb sex also had very little effect on the ewe–lamb relationship. Previous studies have suggested that male lambs tend to be further from the ewe than female lambs ŽGrubb and Jewell, 1966; Shillito-Walser and Williams, 1986., perhaps leading up to the dissociation of male lambs from the matrilineal group ŽHunter and Milner, 1963; Arnold and Pahl, 1974.. It may be that the lambs used in the present study were too young to begin the process of natural weaning and sexual segregation. Although the lambs were the same age as the twin lambs used by Shillito-Walser and Williams Ž1986., they were all singletons which tend to be weaned at a later age than twins ŽPrice et al., 1984.. The differential attachment of male and female lambs was evident only in the Suffolk ewe with Suffolk lamb group ŽSS.. Whether this group is more likely to wean their lambs earlier than other groups is not known. Alternatively, the castration of male lambs may have abolished any sex differences in ewe–lamb association. The non-random nature of ewe associations is consistent with other observations ŽArnold and Pahl, 1974; Arnold et al., 1981.. Segregation of the two ewe breeds was clearly demonstrated in both environments. Several studies have shown that, although same-breed groups integrate within 3 weeks ŽArnold and Pahl, 1974., flocks composed of different breeds remain permanently separate ŽWinfield and Mullaney, 1973; Arnold and Pahl, 1974; Shillito-Walser and Hague, 1981.. The present study suggests that no significant breed integration occurs during 4 months of contact although some individual animals were observed to form long-term associations with ewes of the other breed ŽC. Dwyer, unpublished observation.. Sheep appear to recognise individual animals by both visual ŽKendrick et al., 1995. and olfactory cues ŽArnold, 1985., with group identity possibly being maintained predominantly by odour. A breed identity seems to be established by using mainly visual cues and probably develops by lambs learning to recognise the appearance of their mothers ŽShillito-Walser, 1980.. This suggests that, whilst integration of same-breed groups occurs with time, as odour cues change, integration of different breed groups will not occur. This hypothesis would predict that the embryo transfer lambs used in the present study will have the breed identity of their mothers, regardless of their own breed.
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The ewe’s own lamb was the most frequent nearest neighbour, with other lambs either being actively avoided by the ewe or simply not encountered as they tended to remain close to their own mothers. The ewe–lamb relationship appeared to be dictated by the behaviour of the ewe with lamb breed having no significant effect on the mean distance between the ewe and lamb. Ewes maintain close spatial relationships with their lambs in the first week after birth ŽMcBride et al., 1967; Morgan and Arnold, 1974; O’Connor, 1990. when the ewe is attentive to the location of her lamb, approaching the lamb very frequently ŽHinch et al., 1987; O’Connor, 1990.. Thereafter the distance between ewe and lamb increases to a plateau by 28–36 days after birth ŽMorgan and Arnold, 1974; O’Connor, 1990., until at least 100 days after birth ŽArnold et al., 1979.. Analysis of ewe and lamb behaviour suggests that the lamb is responsible for more than 80% of approaches and contacts between the pair from week 6 ŽO’Connor, 1990.. The ewe, however, controls the dynamics of the relationship and, as can be seen in the present study, is ultimately responsible for the distance between the ewe and lamb because lambs of different breeds are the same distance from the ewe. The reason why Blackface ewes should maintain closer spatial relationships to their lambs than Suffolk ewes is intriguing. Blackface ewes are known to spend more time grooming and vocalising to their neonatal lambs than Suffolk ewes ŽDwyer and Lawrence, 1998; Dwyer et al., 1998. and may, therefore, have formed a stronger bond with their lamb. In addition to full approaches to their mother, lambs are alert to the behaviour of their mother and make increasing numbers of partial approaches whenever the ewe raises her head ŽO’Connor, 1990.. Blackface-raised lambs were observed to be within 5 m of their mothers on significantly more occasions than Suffolk-raised lambs, suggesting that they more frequently approached their mothers or, having approached, remained with their mothers for longer. This may indicate a higher frequency of ‘head-up’ postures Žthe posture used by the ewe to indicate that the lamb may approach. by the Blackface ewes, although whether this represents a generally greater alertness in Blackface ewes compared to Suffolks or a greater awareness of their lamb is not clear. The general trends in social behaviour between the two breeds are in line with previous observations, that is small subgroup size in the hill breeds and larger subgroups in lowland breeds Že.g., Clun Forest. or no subgrouping in Merinos ŽArnold and Pahl, 1967; Arnold et al., 1981; Shillito-Walser and Hague, 1981.. Furthermore, a closer association within some breeds than others has also been reported in other breeds ŽMerino vs. Wiltshire Horn: Winfield and Mullaney, 1973.. The finding that ewes altered their social behaviour depending on their environment, however, has not been reported before. In Field 2 the subgroup sizes of Blackface ewes were similar to those previously seen in Blackface ewes on an established home range ŽLawrence and Wood-Gush, 1988.. It may be, therefore, that either the size of the field, availability of grass types or the relative lack of topographical features in Field 1 constrained the breed-specific social behaviour of the Blackface such that they made closer associations with other ewes and formed larger subgroups. The Suffolk ewes always formed closer associations with other ewes than Blackfaces and aggregated into a small number of larger subgroups. Surprisingly, however, when placed in the larger field the distance between Suffolk ewes remained the same but subgroup sizes increased further. This clearly demonstrated that the social behaviour of the sheep was not simply a function of
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the available space but suggests that other factors affect the relationships between animals. In Rocky Mountain Bighorn sheep 65% of the variance in spatial distribution of animals was accounted for by environmental variables such as slope, palatability of grasses, elevation and nitrogen content of vegetation ŽShannon et al., 1975.. The selection of a suitable home range by individual animals in a new environment may partly explain both the distribution of animals and the increase in subgroup size for Suffolks in Field 2 compared to Field 1. It seems likely, however, that social relationships between animals also dictate where they establish their home range. Hunter and Davies Ž1963. demonstrated that returning lambs to an already occupied field led to the establishment of new home ranges on underoccupied areas by the incomers that may have been on less favoured areas of the field. Thus it may be that social constraints may prevent animals from making maximal usage of the available vegetation. The differences between the two breeds in their social relationships may be related to physical factors, such as activity patterns, dietary preferences or to some intrinsic breed-specific gregariousness. The present paper has already demonstrated that Blackface ewes form closer relationships to their lambs than Suffolk ewes. Furthermore, it is known that maternal ewes do not react to isolation from adult conspecifics in the presence of their own lamb ŽPoindron et al., 1994.. The closer bond between ewe and lamb in the Blackface may be indicative of a weaker attachment to the flock, at least during the summer months, such that Blackface ewes maintain larger spatial relationships with other ewes than Suffolks. The Merino is more strongly attached to the flock than other breeds and more weakly to their own lamb ŽMcBride et al., 1967.. The Suffolk may represent a point somewhere between the Merino and hill breeds such as the Blackface. Some Blackface ewes were frequently observed to be more than 30 m from any other ewe, with their lamb, and were apparently acting as an individual animal rather than a flock member ŽC. Dwyer, unpublished observation.. Grubb and Jewell Ž1966. suggest that in feral Soay sheep the flocking instinct is not strong and Soays tend to act as individuals when alarmed. They suggest that increasing domestication has produced animals that are tolerant to crowding. Thus selection for production characteristics may have indirectly selected for animals, such as the Suffolk, that are more gregarious. Although ewes adopted largely overlapping distributions in Field 1, when given access to a larger and more diverse environment in Field 2 the two breeds used mostly separate areas of the field. Blackface ewes used predominantly the upland areas of the field and appeared to range over a larger area than Suffolks who confined themselves to a relatively small area in the lowland part of the field. It is possible that the preferred qualities of a home range for Blackface ewes were abundant in Field 2 but restricted to a small area for Suffolk ewes. The ewes used in this study were obtained as 1-year olds from typical hill ŽBlackface. and lowland ŽSuffolk. farms. Their early grazing experiences may have conditioned them to certain grass types and features of their environment which then influenced their preferred home range in novel fields. The distribution of Suffolk ewes in this study appears to follow the distribution of the best swards of perennial ryegrass and clover in both fields. The Blackface ewes, however, despite grazing the perennial ryegrass sward in Field 1, seemed to prefer the poorer hill grazing of Agrostis, Festuca and Nardus species in Field 2. A cross-fostering study of Welsh
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and Clun Forest ewes and lambs ŽKey and MacIver, 1980. suggested that preferences of lambs for upland grazing, and their dispersal patterns, may be related to their mothers breed and, hence their early life experience. In addition, dietary preferences are known to affect foraging location of lambs ŽScott et al., 1995. in the absence of social preferences. Our ewes, however, were only able to express their preferences in Field 2 when the diverse nature of the grass types and topography provided both a hill and a lowland type location. The greater dispersal of the Blackface ewes in Field 2 may also have been a function of their choice of foraging area as the upland region may have required greater ranging behaviour to obtain a similar nutritional intake. The location and home range behaviour of the embryo transferred lambs in the present study would be expected, if early life experience determined social preferences, to conform to those of their mothers breed rather than their own breed. In conclusion, this study has demonstrated that the social organization and dispersal of ewes varies according to breed. Furthermore, the nature of their social behaviour and subgrouping can be modified by environment although the direction of change differed between breeds. These results clearly demonstrate that social organization is more complex than a simple function of available space. Blackface ewes were significantly less gregarious than Suffolk ewes which may be related to the relative domestication, or husbandry, of the two breeds. It is possible, however, that early life experience may have dictated the subsequent foraging choices made by ewes and that these affected social associations indirectly through greater dispersal and ranging of ewes eating less nutritious plant species. Further studies on the social behaviour of the embryo-transfer lambs used in this study may help to distinguish between the effects of experience and intrinsic differences between breeds. The relationship of the ewe to her lamb was more resistant to environmental influence than her relationship to other adult ewes. Blackface ewes maintain closer spatial contact with their lambs than Suffolk ewes which may be related to closer associations being formed immediately after birth. The flexibility in the social relationships formed by sheep may have adaptive significance for the movement of animals into new environments.
Acknowledgements The authors would like to thank the following: Jack FitzSimons and Mark Ramsay for animal husbandry, Hazel Brown for assistance with observations in Year 1, Sandy Clelland for providing the botanical analysis of the fields; John Boyd for his assistance with the maps of the fields, and Edinburgh Genetics for performing the embryo-transfer procedures. This study was supported by the Scottish Office Agriculture, Environment and Fisheries Department.
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