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Social interactions in N'dama cows during periods of idling and supplementary feeding post-grazing
Applied Animal Behaviour Science, 34 ( 1992 ) I 1-22 Elsevier Science Publishers B.V., Amsterdam
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Social interactions in N'dama cows during periods of idling and supplementary feeding post-grazing J.D. K a b u g a Department of Animal Science, University of Science and Technology, Kumasi, Ghana (Accepted 25 November 1991 )
ABSTRACT Kabuga, J.D., 1992. Social interactions in N'dama cows during periods of idling and supplementary feeding post-grazing. Appl. Anita. Behav. Sci., 34:11-22. Thirty N'dama cows were observed post-grazing, during periods of idling (NF) and periods of supplementary feeding (F), over a l-year period to determine the frequency and pattern of social interactions during 1 h each of feeding and idling. Agonistic interactions (butting, threatening and avoidance) were 1.4 times higher (P<0.01) in the F than the NF. In contrast, amicable behaviours (rubbing, sniffing and grooming) were significantly (P<0.05) higher in the NF than F. The frequency ofagonistic interactions was highest during the first 30 min of the F when feed was available. There was no trend in the frequency of either agonistic or amicable bebaviours during the NF. During the first 15 min of the F, animals initiated no amicable behaviours, but thereafter amicable behaviours sharply increased until the end of the period. Season (dry and rainy) had no influence on frequency of agonistic behaviours but grooming, and thus all amicable behaviours combined, were significantly (P< 0.05) higher in the rainy rather than dry season. As butting areas, animals preferred the sides (39-42%) and rear of companion animals (25-28%). Social dominance was highly correlated with liveweight (r=0.828-0.884) and age (r=0.664-0.754); this was not linear, and tended to be complex. High-ranking animals initiated most, but received few, agonistic interactions. Agonistic interactions were generally between animals close in rank or with subordinates. There was no significant (P> 0.05 ) relationship between number of animals dominated and amicable behaviours initiated or received.
INTRODUCTION I t is w e l l e s t a b l i s h e d i n m o s t s p e c i e s o f d o m e s t i c a n i m a l s t h a t a g g r e s s i o n is high when animals compete for scarce resources such as feed and water (Craig, 1981 ). T h e l e v e l o f a g g r e s s i o n is, h o w e v e r , d e p e n d e n t o n t h e p a l a t a b i l i t y o f the feed on offer, the spatial distribution of the feed, and the temporal limi-
Correspondence to." J.D. Kabuga, Department of Animal Science, University of Science and Technology, Kumasi, Ghana.
© 1992 Elsevier Science Publishers B.V. All rights reserved 0168-1591/92/$05.00
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J.D. KABUGA
tations of the feed, i.e. for how long in the day the feed is available, and social factors such as mutual social tolerance of the herd as determined by age and social experience (Metz, 1983 ). Data on the level of aggression during competition of cattle for feed has mostly been obtained from dairy cattle fed concentrate before forage (Schein and Fohrman, 1955; Metz, 1983), from beef cattle fed early in the morning while at pasture (Wagnon, 1965), or from beef cattle competing for feed (Arnold and Grassia, 1982/1983). Under most of these conditions animals were probably hungry and this resulted in increased competition and aggression. Few studies have examined the level of aggression when feed is supplemented in the evenings after grazing and before the cattle are corraled for the night, even though this may be the best schedule of feeding forage for efficient utilization. Experiments indicate that supplementary concentrates can result in a reduction in forage dry matter intake owing to substitution effects (Leaver, 1985). Most studies have also concentrated on the level of aggression during supplementary feeding with the result that few data are available on other social behaviours such as amicable (affiliative) behaviours. Furthermore, seasonal and long-term effects on the level of social interactions have not been seriously studied. If we are to understand the effect of supplementary feeding on social interactions then all these factors need to be examined. The social interactions of a small herd of N'dama cows during idling and when supplemented with wet brewers' spent grain, in the evening after grazing, over a 1-year period are reported. ANIMALS, MATERIALS AND METHODS
Location
The experiment was carried out at Boadi, 8 km from the city of Kumasi (6°43'N; 1 °36'W), in the humid zone of Ghana. Details of the climate of the area have been reported previously (Kabuga and Alhassan, 1981 ). Briefly, the climate is hot and humid and rainfall is bimodally distributed with an annual mean of about 1200 mm. The major rainy season (April-July) reaches its peak in May and June. A short dry season occurs in August followed by a minor rainy season (September-October). The dry season lasts from November to March. Animals
Thirty N'dama cows, average age 75.9 months (range 36-185 months), were used for the experiment. The cows on average weighed 239 kg (range 200-350 kg). The cows were from a group of animals which had been ban-
SOCIAL INTERACTIONS IN N'DAMA COWS
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died as a single herd for 9 years at the Boadi Dairy/Beef Cattle Research Station. All cows had been dehorned at birth and were individually ear tagged with large yellow ear tags for easy identification. The experimental animals were grazed with the main herd from 08:30 to 14:30 h. They were separated from the main herd for the experiment at 15:00 h when the herd was corraled for the night.
Observation techniques The cows were observed twice weekly on Sundays and Wednesdays from April 1990 to March 1991, a total of 212 h. Daily observations lasted 2 h. A 1-h observational period was designated during non-feeding (idling; NF), when no supplementary feed was provided, and during a feeding period (F) when supplementary feed was given. The supplementary feed consisted of wet brewers' spent grain, 5 kg of which was given daily to each experimental animal, provided in six feeding troughs in a 20 m × I0 m pen. The feeding troughs were arranged three to each of the long sides of the pen. The troughs varied in length, but were all 0.6 m wide. The total length of the six troughs was 18.6 m. Both the NF and F took place in the feeding pen. The NF always preceded the F and was between 15:00 and 16:00 h, while the F was between 16:30 h and 17:30 h. Observations were started 2 min after all animals had assembled in the pen either for idling or for eating. Two major attributes of social behaviour were recorded. These were agonistic behaviours made up of butting, threatening and avoidance (there were no fights) and amicable behaviours comprising allogrooming, sniffing the genital area and rubbing. All behaviours were recorded as they happened and the identities of the performing and receiving animals noted. The body areas of animals butted were also recorded. Four observers and one recorder were used during each observational day.
Analysis All agonistic behaviours for each period were separately pooled and these interactions were noted in a sociometric matrix, where emitting and receiving individuals were specified. From this matrix, the n u m b e r of cows who were dominated, and the ratio of agonistic interactions originated by an animal to the total n u m b e r of agonistic interactions in which an animal was involved ( A I : A T ) , were calculated separately for each cow in the NF and F. Dominance ranks were determined from the n u m b e r of animals dominated. This m e t h o d was found to result in less variations in the rankings between the NF and F than using AI/AT. From the ranks the herd was divided into three equal groups of high (H)-, m e d i u m (M)- and low (L)-ranking cows.
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J.D. KABUGA
Spearman's rank correlation (rs) (Siegel, 1956) was used to test for correlations between ranked data while Pearson's product-moment correlation (r) was applied to test for correlations between continuous data. Data from the various attributes of social interactions were analysed by analysis of variance (Steel and Torrie, 1960) to determine the relative importance of periods (NF vs. F), seasons (dry vs. rainy) and their interacting influences on the frequency of these behaviours. The data were not normally distributed and were log transformed before analysis. However, all means quoted are actual values. To examine if observed frequencies of behaviours between groups were comparable with expected frequencies, Chi-square (X2) analysis was used. RESULTS
Difference in frequency of social interactions duringfeeding and non-feeding periods A total of 28 032 agonistic interactions and 2448 amicable behaviours were observed in both the F and NF during the experiment. About 59% ofagonistic interactions and 61% of amicable behaviours occurred in the F and NF, respectively. All animals were involved in these social interactions, but with a high level of variation between individuals. Analysis of variance indicated that except for avoidance there were significant ( P < 0 . 0 1 ) differences between the F and NF in frequencies of threats, butts and all agonistic interactions combined (threats, butts and avoidances), with frequencies being higher in the F than NF (Table 1 ). By contrast, except for allogrooming, all amicable behaviours combined, including rubbings and sniffings, were significantly ( P < 0.05 ) higher in the NF than F. The frequency pattern of social interactions for the l-h periods of observation differed between the F and NF. All agonistic interactions combined were highest shortly after feeding but declined during the first 30 rain of the F to fairly stable levels by 40 min post-feeding (Fig. 1 ( A ) ) . This pattern was due to changes in the level of buttings; threats and avoidances remained almost constant throughout the period of observation. By contrast, the frequency pattern of agonistic interactions in the NF was irregular, with no definite trend (Fig. 1 (B)). Threats and avoidances in this period also tended to be evenly distributed over time. There were no amicable behaviours during the first 15 min of the F. Thereafter, however, the combined amicable behaviours increased sharply throughout the period (Fig. 2 ( A ) ) . In the NF the frequency pattern of amicable behaviours over time was variable. These were high during the first 20 min of observation, declined during the next 10 min, then increased and de-
SOCIAL INTERACTIONS IN N'DAMA COWS
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TABLE 1 Effects of season (S) and periods (P) of feeding (F) or non-feeding ( N F ) on social behavioural attributes (frequencies per animal per h )
Behaviour
Butting Threatening Avoidance Agonistic Grooming Rubbing Sniffing Amicable
Season (S) Dry period (P)
Rainy period
Level of significance
F
NF
F
NF
SE
4.41 1.33 0.23 5.97 0.08 0.03 0.03 0.14
1.98 0.86 0.30 3.08 0.12 0.13 0.08 0.33
4.43 1.14 0.38 5.96 0.25 0.04 0.07 0.36
1.54 0.60 0.43 2.58 0.28 0.11 0.13 0.52
0.392 0.133 0.057 0.265 0.051 0.020 0.018 0.040
S
P
S×P
* *
*
*P< 0.05; **P< 0.01.
clined again before finally increasing sharply at the end of the period (Fig. 2(A)). Animals preferred certain parts of the body to be butted (Fig. 2 (B) ). The most preferred butting body areas were the sides (flanks) (39-42%), followed by the rear (25-28%), with the head (5-7%) being the least-preferred area. These preferences were significantly (X2= 61.31 (NF), 37.73 ( F ) ) different between the body parts.
Differences between seasons in frequency of social attributes Except for avoidance, which was higher ( P < 0.05 ) in the rainy rather than the dry season, there were no significant ( P > 0.05 ) differences between seasons in other attributes of agonistic behaviour (Table 1 ). Season × period interactions in relation to ag.onistic behaviour were low and not significant. The frequency of allogrooming and all amicable behaviours combined were significantly (P<0.05) higher in the rainy rather than the dry season. Seasonal differences in rubbings and sniffings were small (P> 0.05 ).
Social dominance Social hierarchies calculated for the F and NF based on number of animals dominated were more highly correlated (rs= 0.964) between the two periods than those calculated from AI/AT (rs= 0.878 ). These social hierarchies, using both methods, were not completely linear. The first eight high-ranking animals showed a linear hierarchy, but thereafter triangular (animal A butts
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J.D, KABUGA
A:
FEEDING
B:
NON-FEEDING
25,
20 ¸
15
10
5
O
10
~b
2o
3o ~'o TIME (MINUTES)
So
6o
Fig. 1. Changes in frequencies of butting ( × ), threatening ( • ), avoidance (O) and all agonistic interactions combined (/x ) during (A) feeding, and (B) non-feeding. B butts C butts A) and circular (as for triangular but with more than 3 animals) relationships were present. The directions of social interactions determined by ranking animals into low (L), m e d i u m ( M ) and high (H) groups are shown in Fig. 3 (A) for both the F and NF. The H-group initiated the highest proportion of agonistic interactions but received the lowest interactions of the three groups. By contrast, the L-group initiated the lowest proportion of agonistic interaction of the groups, but was similar to the M-group in the proportion of interactions received. The highest proportion of interactions initiated by the H-group were directed towards the M-group, with similar levels of aggression directed towards the L- and H-groups (Table 2). The L-group initiated no interactions
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SOCIAL I N T E R A C T I O N S IN N ' D A M A C O W S
A:
AMICABLE
BEHAVIOUR
a. 2.0" D o
1.8. 0 ~
1.2.
w
~. 0.8' O Q: Ld
~
0.4
z 0.~
~b
2'o
~o
,~o
~,o
go
TIME (MINUTES)
FEEDING 50 ¸
NON- FE EDING[~
-T
40 ¸
\
\
\
\\'
_z 30.
\\ \ ',, \
u_ 2 0 o
10'
\ NECK
HEAD
SHOULDER SIDE BODY PART BUTTED
THIGH
REAR
Fig. 2. (A) changes in frequencies of all amicable behaviours combined during feeding (O) and non-feeding ( × ) periods. (B) percentageofbuttings directed to differentparts of the body during feeding and non-feeding. while the M-group initiated a very low (2%) proportion of interactions against the H-group. The M-group initiated the highest proportion (45-50%) of all amicable behaviours combined compared with the L- and H-groups (Fig. 3 ( B ) ) , but this was about equally given to all groups (Table 3 ). All groups were similar in the proportion of amicable behaviours received. Also, all groups initiated amicable behaviours with subordinates, peers and superiors although this was significantly different ( P < 0.01 ) between some groups (Table 3 ).
Relationships between physical and behavioural attributes Liveweight and age at the beginning of the study were strongly correlated ( P < 0.01 ), respectively, with agonistic behaviours initiated (r=0.588, 0.663 )
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J.D. AGONISTIC
A:
BEHAVIOUR
FEEDING NON-FEEDING
-
-
INITIATED
-
KABUGA
- -
-
[]
R E C E I V E D - -
60-
~0"
20
o
cc
uJ B:
Z
AMICABLE
BEHAVIOUR
FEEDING NON- FEEDING
60 ¸
--
INITIATED -
RECEIVED--
-
40 ¸
20 ¸
L
M
J
L
M
H
RANK
Fig. 3. Percentage of social interactions initiated or received by low (L), medium (M) and high ( H ) dominance-ranking animals during feeding and non-feeding. (A) agonistic behaviour. ( B ) amicable behaviour.
and received ( r = - 0 . 5 0 2 , - 0 . 5 3 1 ) and number of animals dominated (r=0.884, 0.754), but not with amicable behaviours initiated (r=0.277, 0.200) and received (r= 0.032, 0.134) in the F. Similarly, in NF, liveweight and age were significantly ( P < 0.05 ) correlated, respectively, with agonistic interactions initiated (r=0.392, 0.502) and received (r= - 0 . 5 7 3 , - 0 . 5 9 3 ) , and number of animals dominated (r=0.828, 0.664), but not amicable behaviours initiated (r= - 0.030, - 0.004) and received (r= - 0.066, 0.148 ). Amicable behaviours initiated and received were highly correlated (r= 0.719; P < 0 . 0 1 ) in the Fbut not the NF ( r = 0 . 1 2 3 ; P > 0 . 0 5 ) .
SOCIAL INTERACTIONS IN N'DAMA COWS
19
TABLE 2 Percentage of interactions between different social rank (L, low; M, medium; H, high) groups of animals during periods of feeding (F) and non-feeding (NF) Rank combinations a
Social attributes Butting
LL LM LH ML MM MH HL HM HH t'Z2
Threatening
Avoidance
Agonistic
F
NF
F
NF
F
NF
F
NF
9.9 3.4 0.0 15.5 13.5 2.1 17.6 24,4 13,6 46,2
13.2 2.7 0.0 17.6 7.6 1.6 18.1 22.2 17.1 49.6
4.3 1.1 0.0 16.1 16.5 2.0 22.0 23.6 14.4 62.4
9.5 2.2 0.0 20.4 13.8 3.1 18.7 19.3 12.9 44.3
4.7 2.0 0.0 13.5 16.5 3.0 18.9 25.2 16.1 56.9
5.5 2.0 0.0 14.4 9.9 2.4 11.6 23.1 31.0 78.1
8.7 2.9 0.0 15.4 14.2 2.1 18.4 24.3 14.0 49.4
11.1 2.5 0.0 17.6 9.3 2.0 17.6 21.7 18.6 47.8
~Interactions initiated by first letter group, e.g. LM = low-rank animal initiated interaction with medium-rank animal. bZ2 = 15.5, P < 0.05; Z 2 = 20.1, P < 0.01, e.g. for Z 2 = 46.2 buttings between rank groups are significantly different ( P < 0 . 0 1 )
TABLE 3 Percentage of interactions between different social rank (L, low: M, medium; H, high) groups of animals during periods of feeding (F) and non-feeding ( N F ) Rank combinations a
LL LM LH ML MM MH HL HM HH bZ2
Social attributes Grooming
Rubbing
Sniffing
Amicable
F
NF
F
NF
F
NF
F
NF
1.9 3.9 4.4 14.6 20.5 26.3 9.3 12.2 6.8 48.3
13.9 12.7 1.2 26.1 19.6 18.4 2.4 1.6 4.1 60.7
3.2 3.2 6.5 19.4 3.2 6.5 12.9 22.6 22.6 50.9
4.5 12.0 3.0 18.0 9.0 9.0 9.8 10.5 24.1 30.4
8.0 2.0 8.0 6.0 6.0 4.0 26.0 16.0 24.0 55.9
12.5 7.9 9.2 6.6 3.9 10.5 9.9 17.1 22.4 22.7
3.1 3.5 5.2 13.6 16.1 20.3 12.6 14.0 11.5 25.6
11.1 11.1 4.0 18.5 12.5 13.8 6.4 8.3 14.3 14.0
alnteractions initiated by first letter group, e.g. LM =low-rank animal initiates interaction with medium-rank animal. b X-= 15.5, P < 0.05: Z2= 20.1, P < 0.01, e.g. for X2= 48.3 groomings between rank groups are significantly different ( P < 0 . 0 1 )
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J,D. KABUGA
DISCUSSION
It is clear from the present results that the supplementary feeding provided post-grazing was for a large part responsible for the high level of aggression during the feeding period observed. There were 1.4 times as many agonistic interactions during the F than NF. Agonistic behaviours were also highest during the first 30 min of observation when feed was available. It is also unlikely that a limited feeding space accounted for a significant part of the high level of aggression. Animals were provided with 62 cm of trough space per cow and this conforms to the 60-70 cm manger space per animal recommended for cows larger than the present experimental animals (British Standards Institute, 1979 ). Furthermore, these troughs were wide enough to allow animals to eat simultaneously on both sides of the trough. These results thus parallel previous studies which observed that supplementary feeding provided at only one locality and for a limited time of day results in competition and increased aggression (Metz, 1983). These data therefore suggest that there is no advantage in post-grazing feeding with a view to reducing the level of aggression at the feed troughs. This may not necessarily be so. It is likely that pre-grazing feeding would have resulted in a higher level of aggression than observed here because animals would be hungrier leading to more competition and aggression (Craig, 1981 ; Metz, 1983 ). The contribution of butting to the total number of agonistic interactions declined from 79% during the first 30 min to 68% during the second 30 rain in the F, as compared to about 60% throughout the NF (Fig. 1 (A) and 1 (B)). This high level of butting in both periods is contrary to reports that in wellestablished cow groups threats and passive avoidance are the main patterns of aggressive behaviour used to maintain social rank (Hafez and Bouissou, 1975 ). These animals were from a single herd so one would have expected a well-established hierarchy. Furthermore, common rearing experience and family relationships of some members of the group should have resulted in lower levels of aggression due to mutual tolerance (Bouissou and Andrieu, 1978; Reinhardt and Reinhardt, 1981). These results are, however, not unique. Kabuga et al. ( 1991 ) had previously reported the aggressiveness of N'dama cows even under grazing conditions. It is also apparent from the investigation that feeding elicited mostly agonistic behaviours and very little affiliative behaviours. However, immediately post-feeding the level of affiliative behaviours increased sharply above levels observed in the NF. One could speculate that animals were mending cohesive bonds disrupted or disturbed during the period of food competition. This speculation has some support from the high correlation between amicable behaviours initiated and received only in the F. The preferential butting of the sides by animals is consistent with the suggestion (Hafez and Bouissou, 1975 ) that this generally elicits flight and sub-
SOCIAL INTERACTIONS IN N'DAMA COWS
21
mission. However, the preferential butting of the sides and rear when animals were eating with their heads deep in the trough lead to some interesting questions concerning individual recognition with respect to dominant-subordinate relationships. Either these animals were able to identify conspecifics from the rear or sides or else other means such as olfactory cues (Syme and Syme, 1979 ) were used under these conditions. An unexpected finding in this trial was the lack of seasonal influence on the level of agonistic behaviours during feeding. One would have predicted that because of the poorer quality and quantity of forage in the dry season animals would be more hungry, resulting in more competition and aggression in the dry season compared with the rainy season. It may be that there is an optim u m level of aggression beyond which there may be no benefit in feed intake to the emitter of aggression. Alternatively, mutual aggression in this study may have reached a stable level (Metz, 1983) in the group before the investigation started. This experiment was initiated 6 months after supplementary feeding was introduced into the main herd. Cows initiated more grooming but not sniffing and rubbing in the rainy season compared with the dry season (Table 1 ). Grooming serves the function of removing noxious substances (faeces, urine and m u d ) and ectoparasites from the skin (Hafez and Bouissou, 1975). Since mud and ectoparasites are more prevalent in the rainy season, animals probably solicited and received more grooming from conspecifics. The l-year observation of the herd allowed us an insight into the nature of social dominance. Observations showed that at any particular time agonistic interactions were uni-directional, suggesting stability in the dominance hierarchy. However, over the l-year period there were some reversals in dominance ranks, as observed from reversals in agonistic interactions in 3% out of 435 dyads. Dominance was found to be complex rather than linear, despite the strong positive correlation of age and liveweight with number of animals dominated (Schein and Fohrman, 1955; Bouissou, 1972 ). This may have been due to the similarity of age and therefore physique and experience of some herd members (Syme and Syme, 1979). Some changes in rank were caused by illness and weight loss due to lactation. An interesting example was cow number 9 which, 7 months after the start of the trial, dropped from the first to the third position in rank when she calved and had a retained placenta. However, by the end of the investigation she was back to the second position in rank. These results are, therefore, at variance with results of previous studies which showed that in cattle herds rankings once established are very stable (Schein and Fohrman, 1955; Bouissou, 1972 ). Differences between our study and these results may be due to differences in the breed of cows used. In these studies Bos taurus dairy breeds were used. In this investigation there was a lack of significant relationship between dominance ranks and amicable behaviours such as grooming, in contrast to
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J.D, KABUGA
other studies (Hafez and Bouissou, 1975; Hart, 1985 ). The lack of relationship in the present trial was probably the result of family relationships in the herd. Some young cows in the L group were daughters of cows in the H group but received most of their grooming from their mothers. ACKNOWLEDGEMENTS
The authors wishes to thank the management of the Boadi Dairy/Beef Cattle Research Station for providing facilities for the experiment, P. Yawkpe, Owusu-Ansah, D. Akumsa and my sons Collin and Mike for their help with observations, and Gladys A. Ndziba for typing the manuscript. REFERENCES Arnold, G.W. and Grassia, A., 1982/1983. Social interactions amongst beef cows competing for food. Appl. Anim. Ethol., 9: 239-252. Bouissou, M.F., 1972. Influence of bodyweight and presence of horns on social rank in domestic cattle. Anim. Behav., 20: 474-477, Bouissou, M.F. and Andrieu, S., 1978. Establissement des relations preferentielles chez les bovins domestiques. Behaviour, 54:148-157. British Standards Institute, 1979. For the Design of Buildings and Structures for Agriculture, Part II, Code 5502, p. 11. Craig, J.V., 1981. Domestic Animal Behaviour. Prentice-Hall, Englewood Cliffs, N J, pp. 145195. Hafez, E.S.E. and Bouissou, M.F., 1975. The behaviour of cattle. In: E.S.E. Hafez (Editor), The Behaviour of Domestic Animals. Bailliere, Tindall and Cox, London, pp. 203-245. Hart, B.L., 1985. The Behaviour of Domestic Animals. W.H. Freeman, New York, pp. 55-74. Kabuga, J.D. and Alhassan, W.S., 1981. Reproductive performance of Canadian Holsteins in the Tropics. World Rev. Anim. Prod., 17: 41-48. Kabuga, J.D., Gari-Kwaku, J. and Annor, S.Y., 1991. Social status and its relationship to maintenance behaviour in a herd of N'dama and West African Shorthorn cattle. Appl. Anita. Behav. Sci., 31: 169-181. Leaver, J.D., 1985. Milk production from grazed temperate grassland. J. Dairy Res., 52: 313344. Metz, J.H.M., 1983. Food competition in cattle. In: S.H. Baxter, M.R. Baxter and J.A.D. MacCormack (Editors), Farm Animal Housing and Welfare. Martinus Nijhoff, The Hague, pp. 164-170. Reinhardt, V. and Reinhardt, A., 1981. Cohesive relationships in a cattle herd (Bos indicus). Behaviour, 77: 121-151. Schein, M.W. and Fohrman, M.H., 1955. Social dominance relationships in a herd of dairy cattle. Br. J. Anim. Behav., 3: 45-55. Siegel, S., 1956. Non-Parametric Statistics for the Behavioural Sciences. McGraw-Hill, New York. Steel, R.G.D. and Torrie, J.H., 1960. Principles and Procedures of Statistics. McGraw-Hill, New York. Syme, G.J. and Syme, L.A., 1979. Social Structure in Farm Animals. Elsevier, New York, pp. 45-56. Wagnon, K.A., 1965. Social Dominance in Range Cows and its Effect on Supplemental Feeding. California Agricultural Experimental Station, Bulletin no. 819, University of California, Davis, USA.
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Social interactions in N'dama cows during periods of idling and supplementary feeding post-grazing J.D. K a b u g a Department of Animal Science, University of Science and Technology, Kumasi, Ghana (Accepted 25 November 1991 )
ABSTRACT Kabuga, J.D., 1992. Social interactions in N'dama cows during periods of idling and supplementary feeding post-grazing. Appl. Anita. Behav. Sci., 34:11-22. Thirty N'dama cows were observed post-grazing, during periods of idling (NF) and periods of supplementary feeding (F), over a l-year period to determine the frequency and pattern of social interactions during 1 h each of feeding and idling. Agonistic interactions (butting, threatening and avoidance) were 1.4 times higher (P<0.01) in the F than the NF. In contrast, amicable behaviours (rubbing, sniffing and grooming) were significantly (P<0.05) higher in the NF than F. The frequency ofagonistic interactions was highest during the first 30 min of the F when feed was available. There was no trend in the frequency of either agonistic or amicable bebaviours during the NF. During the first 15 min of the F, animals initiated no amicable behaviours, but thereafter amicable behaviours sharply increased until the end of the period. Season (dry and rainy) had no influence on frequency of agonistic behaviours but grooming, and thus all amicable behaviours combined, were significantly (P< 0.05) higher in the rainy rather than dry season. As butting areas, animals preferred the sides (39-42%) and rear of companion animals (25-28%). Social dominance was highly correlated with liveweight (r=0.828-0.884) and age (r=0.664-0.754); this was not linear, and tended to be complex. High-ranking animals initiated most, but received few, agonistic interactions. Agonistic interactions were generally between animals close in rank or with subordinates. There was no significant (P> 0.05 ) relationship between number of animals dominated and amicable behaviours initiated or received.
INTRODUCTION I t is w e l l e s t a b l i s h e d i n m o s t s p e c i e s o f d o m e s t i c a n i m a l s t h a t a g g r e s s i o n is high when animals compete for scarce resources such as feed and water (Craig, 1981 ). T h e l e v e l o f a g g r e s s i o n is, h o w e v e r , d e p e n d e n t o n t h e p a l a t a b i l i t y o f the feed on offer, the spatial distribution of the feed, and the temporal limi-
Correspondence to." J.D. Kabuga, Department of Animal Science, University of Science and Technology, Kumasi, Ghana.
© 1992 Elsevier Science Publishers B.V. All rights reserved 0168-1591/92/$05.00
12
J.D. KABUGA
tations of the feed, i.e. for how long in the day the feed is available, and social factors such as mutual social tolerance of the herd as determined by age and social experience (Metz, 1983 ). Data on the level of aggression during competition of cattle for feed has mostly been obtained from dairy cattle fed concentrate before forage (Schein and Fohrman, 1955; Metz, 1983), from beef cattle fed early in the morning while at pasture (Wagnon, 1965), or from beef cattle competing for feed (Arnold and Grassia, 1982/1983). Under most of these conditions animals were probably hungry and this resulted in increased competition and aggression. Few studies have examined the level of aggression when feed is supplemented in the evenings after grazing and before the cattle are corraled for the night, even though this may be the best schedule of feeding forage for efficient utilization. Experiments indicate that supplementary concentrates can result in a reduction in forage dry matter intake owing to substitution effects (Leaver, 1985). Most studies have also concentrated on the level of aggression during supplementary feeding with the result that few data are available on other social behaviours such as amicable (affiliative) behaviours. Furthermore, seasonal and long-term effects on the level of social interactions have not been seriously studied. If we are to understand the effect of supplementary feeding on social interactions then all these factors need to be examined. The social interactions of a small herd of N'dama cows during idling and when supplemented with wet brewers' spent grain, in the evening after grazing, over a 1-year period are reported. ANIMALS, MATERIALS AND METHODS
Location
The experiment was carried out at Boadi, 8 km from the city of Kumasi (6°43'N; 1 °36'W), in the humid zone of Ghana. Details of the climate of the area have been reported previously (Kabuga and Alhassan, 1981 ). Briefly, the climate is hot and humid and rainfall is bimodally distributed with an annual mean of about 1200 mm. The major rainy season (April-July) reaches its peak in May and June. A short dry season occurs in August followed by a minor rainy season (September-October). The dry season lasts from November to March. Animals
Thirty N'dama cows, average age 75.9 months (range 36-185 months), were used for the experiment. The cows on average weighed 239 kg (range 200-350 kg). The cows were from a group of animals which had been ban-
SOCIAL INTERACTIONS IN N'DAMA COWS
|3
died as a single herd for 9 years at the Boadi Dairy/Beef Cattle Research Station. All cows had been dehorned at birth and were individually ear tagged with large yellow ear tags for easy identification. The experimental animals were grazed with the main herd from 08:30 to 14:30 h. They were separated from the main herd for the experiment at 15:00 h when the herd was corraled for the night.
Observation techniques The cows were observed twice weekly on Sundays and Wednesdays from April 1990 to March 1991, a total of 212 h. Daily observations lasted 2 h. A 1-h observational period was designated during non-feeding (idling; NF), when no supplementary feed was provided, and during a feeding period (F) when supplementary feed was given. The supplementary feed consisted of wet brewers' spent grain, 5 kg of which was given daily to each experimental animal, provided in six feeding troughs in a 20 m × I0 m pen. The feeding troughs were arranged three to each of the long sides of the pen. The troughs varied in length, but were all 0.6 m wide. The total length of the six troughs was 18.6 m. Both the NF and F took place in the feeding pen. The NF always preceded the F and was between 15:00 and 16:00 h, while the F was between 16:30 h and 17:30 h. Observations were started 2 min after all animals had assembled in the pen either for idling or for eating. Two major attributes of social behaviour were recorded. These were agonistic behaviours made up of butting, threatening and avoidance (there were no fights) and amicable behaviours comprising allogrooming, sniffing the genital area and rubbing. All behaviours were recorded as they happened and the identities of the performing and receiving animals noted. The body areas of animals butted were also recorded. Four observers and one recorder were used during each observational day.
Analysis All agonistic behaviours for each period were separately pooled and these interactions were noted in a sociometric matrix, where emitting and receiving individuals were specified. From this matrix, the n u m b e r of cows who were dominated, and the ratio of agonistic interactions originated by an animal to the total n u m b e r of agonistic interactions in which an animal was involved ( A I : A T ) , were calculated separately for each cow in the NF and F. Dominance ranks were determined from the n u m b e r of animals dominated. This m e t h o d was found to result in less variations in the rankings between the NF and F than using AI/AT. From the ranks the herd was divided into three equal groups of high (H)-, m e d i u m (M)- and low (L)-ranking cows.
14
J.D. KABUGA
Spearman's rank correlation (rs) (Siegel, 1956) was used to test for correlations between ranked data while Pearson's product-moment correlation (r) was applied to test for correlations between continuous data. Data from the various attributes of social interactions were analysed by analysis of variance (Steel and Torrie, 1960) to determine the relative importance of periods (NF vs. F), seasons (dry vs. rainy) and their interacting influences on the frequency of these behaviours. The data were not normally distributed and were log transformed before analysis. However, all means quoted are actual values. To examine if observed frequencies of behaviours between groups were comparable with expected frequencies, Chi-square (X2) analysis was used. RESULTS
Difference in frequency of social interactions duringfeeding and non-feeding periods A total of 28 032 agonistic interactions and 2448 amicable behaviours were observed in both the F and NF during the experiment. About 59% ofagonistic interactions and 61% of amicable behaviours occurred in the F and NF, respectively. All animals were involved in these social interactions, but with a high level of variation between individuals. Analysis of variance indicated that except for avoidance there were significant ( P < 0 . 0 1 ) differences between the F and NF in frequencies of threats, butts and all agonistic interactions combined (threats, butts and avoidances), with frequencies being higher in the F than NF (Table 1 ). By contrast, except for allogrooming, all amicable behaviours combined, including rubbings and sniffings, were significantly ( P < 0.05 ) higher in the NF than F. The frequency pattern of social interactions for the l-h periods of observation differed between the F and NF. All agonistic interactions combined were highest shortly after feeding but declined during the first 30 rain of the F to fairly stable levels by 40 min post-feeding (Fig. 1 ( A ) ) . This pattern was due to changes in the level of buttings; threats and avoidances remained almost constant throughout the period of observation. By contrast, the frequency pattern of agonistic interactions in the NF was irregular, with no definite trend (Fig. 1 (B)). Threats and avoidances in this period also tended to be evenly distributed over time. There were no amicable behaviours during the first 15 min of the F. Thereafter, however, the combined amicable behaviours increased sharply throughout the period (Fig. 2 ( A ) ) . In the NF the frequency pattern of amicable behaviours over time was variable. These were high during the first 20 min of observation, declined during the next 10 min, then increased and de-
SOCIAL INTERACTIONS IN N'DAMA COWS
15
TABLE 1 Effects of season (S) and periods (P) of feeding (F) or non-feeding ( N F ) on social behavioural attributes (frequencies per animal per h )
Behaviour
Butting Threatening Avoidance Agonistic Grooming Rubbing Sniffing Amicable
Season (S) Dry period (P)
Rainy period
Level of significance
F
NF
F
NF
SE
4.41 1.33 0.23 5.97 0.08 0.03 0.03 0.14
1.98 0.86 0.30 3.08 0.12 0.13 0.08 0.33
4.43 1.14 0.38 5.96 0.25 0.04 0.07 0.36
1.54 0.60 0.43 2.58 0.28 0.11 0.13 0.52
0.392 0.133 0.057 0.265 0.051 0.020 0.018 0.040
S
P
S×P
* *
*
*P< 0.05; **P< 0.01.
clined again before finally increasing sharply at the end of the period (Fig. 2(A)). Animals preferred certain parts of the body to be butted (Fig. 2 (B) ). The most preferred butting body areas were the sides (flanks) (39-42%), followed by the rear (25-28%), with the head (5-7%) being the least-preferred area. These preferences were significantly (X2= 61.31 (NF), 37.73 ( F ) ) different between the body parts.
Differences between seasons in frequency of social attributes Except for avoidance, which was higher ( P < 0.05 ) in the rainy rather than the dry season, there were no significant ( P > 0.05 ) differences between seasons in other attributes of agonistic behaviour (Table 1 ). Season × period interactions in relation to ag.onistic behaviour were low and not significant. The frequency of allogrooming and all amicable behaviours combined were significantly (P<0.05) higher in the rainy rather than the dry season. Seasonal differences in rubbings and sniffings were small (P> 0.05 ).
Social dominance Social hierarchies calculated for the F and NF based on number of animals dominated were more highly correlated (rs= 0.964) between the two periods than those calculated from AI/AT (rs= 0.878 ). These social hierarchies, using both methods, were not completely linear. The first eight high-ranking animals showed a linear hierarchy, but thereafter triangular (animal A butts
16
J.D, KABUGA
A:
FEEDING
B:
NON-FEEDING
25,
20 ¸
15
10
5
O
10
~b
2o
3o ~'o TIME (MINUTES)
So
6o
Fig. 1. Changes in frequencies of butting ( × ), threatening ( • ), avoidance (O) and all agonistic interactions combined (/x ) during (A) feeding, and (B) non-feeding. B butts C butts A) and circular (as for triangular but with more than 3 animals) relationships were present. The directions of social interactions determined by ranking animals into low (L), m e d i u m ( M ) and high (H) groups are shown in Fig. 3 (A) for both the F and NF. The H-group initiated the highest proportion of agonistic interactions but received the lowest interactions of the three groups. By contrast, the L-group initiated the lowest proportion of agonistic interaction of the groups, but was similar to the M-group in the proportion of interactions received. The highest proportion of interactions initiated by the H-group were directed towards the M-group, with similar levels of aggression directed towards the L- and H-groups (Table 2). The L-group initiated no interactions
17
SOCIAL I N T E R A C T I O N S IN N ' D A M A C O W S
A:
AMICABLE
BEHAVIOUR
a. 2.0" D o
1.8. 0 ~
1.2.
w
~. 0.8' O Q: Ld
~
0.4
z 0.~
~b
2'o
~o
,~o
~,o
go
TIME (MINUTES)
FEEDING 50 ¸
NON- FE EDING[~
-T
40 ¸
\
\
\
\\'
_z 30.
\\ \ ',, \
u_ 2 0 o
10'
\ NECK
HEAD
SHOULDER SIDE BODY PART BUTTED
THIGH
REAR
Fig. 2. (A) changes in frequencies of all amicable behaviours combined during feeding (O) and non-feeding ( × ) periods. (B) percentageofbuttings directed to differentparts of the body during feeding and non-feeding. while the M-group initiated a very low (2%) proportion of interactions against the H-group. The M-group initiated the highest proportion (45-50%) of all amicable behaviours combined compared with the L- and H-groups (Fig. 3 ( B ) ) , but this was about equally given to all groups (Table 3 ). All groups were similar in the proportion of amicable behaviours received. Also, all groups initiated amicable behaviours with subordinates, peers and superiors although this was significantly different ( P < 0.01 ) between some groups (Table 3 ).
Relationships between physical and behavioural attributes Liveweight and age at the beginning of the study were strongly correlated ( P < 0.01 ), respectively, with agonistic behaviours initiated (r=0.588, 0.663 )
18
J.D. AGONISTIC
A:
BEHAVIOUR
FEEDING NON-FEEDING
-
-
INITIATED
-
KABUGA
- -
-
[]
R E C E I V E D - -
60-
~0"
20
o
cc
uJ B:
Z
AMICABLE
BEHAVIOUR
FEEDING NON- FEEDING
60 ¸
--
INITIATED -
RECEIVED--
-
40 ¸
20 ¸
L
M
J
L
M
H
RANK
Fig. 3. Percentage of social interactions initiated or received by low (L), medium (M) and high ( H ) dominance-ranking animals during feeding and non-feeding. (A) agonistic behaviour. ( B ) amicable behaviour.
and received ( r = - 0 . 5 0 2 , - 0 . 5 3 1 ) and number of animals dominated (r=0.884, 0.754), but not with amicable behaviours initiated (r=0.277, 0.200) and received (r= 0.032, 0.134) in the F. Similarly, in NF, liveweight and age were significantly ( P < 0.05 ) correlated, respectively, with agonistic interactions initiated (r=0.392, 0.502) and received (r= - 0 . 5 7 3 , - 0 . 5 9 3 ) , and number of animals dominated (r=0.828, 0.664), but not amicable behaviours initiated (r= - 0.030, - 0.004) and received (r= - 0.066, 0.148 ). Amicable behaviours initiated and received were highly correlated (r= 0.719; P < 0 . 0 1 ) in the Fbut not the NF ( r = 0 . 1 2 3 ; P > 0 . 0 5 ) .
SOCIAL INTERACTIONS IN N'DAMA COWS
19
TABLE 2 Percentage of interactions between different social rank (L, low; M, medium; H, high) groups of animals during periods of feeding (F) and non-feeding (NF) Rank combinations a
Social attributes Butting
LL LM LH ML MM MH HL HM HH t'Z2
Threatening
Avoidance
Agonistic
F
NF
F
NF
F
NF
F
NF
9.9 3.4 0.0 15.5 13.5 2.1 17.6 24,4 13,6 46,2
13.2 2.7 0.0 17.6 7.6 1.6 18.1 22.2 17.1 49.6
4.3 1.1 0.0 16.1 16.5 2.0 22.0 23.6 14.4 62.4
9.5 2.2 0.0 20.4 13.8 3.1 18.7 19.3 12.9 44.3
4.7 2.0 0.0 13.5 16.5 3.0 18.9 25.2 16.1 56.9
5.5 2.0 0.0 14.4 9.9 2.4 11.6 23.1 31.0 78.1
8.7 2.9 0.0 15.4 14.2 2.1 18.4 24.3 14.0 49.4
11.1 2.5 0.0 17.6 9.3 2.0 17.6 21.7 18.6 47.8
~Interactions initiated by first letter group, e.g. LM = low-rank animal initiated interaction with medium-rank animal. bZ2 = 15.5, P < 0.05; Z 2 = 20.1, P < 0.01, e.g. for Z 2 = 46.2 buttings between rank groups are significantly different ( P < 0 . 0 1 )
TABLE 3 Percentage of interactions between different social rank (L, low: M, medium; H, high) groups of animals during periods of feeding (F) and non-feeding ( N F ) Rank combinations a
LL LM LH ML MM MH HL HM HH bZ2
Social attributes Grooming
Rubbing
Sniffing
Amicable
F
NF
F
NF
F
NF
F
NF
1.9 3.9 4.4 14.6 20.5 26.3 9.3 12.2 6.8 48.3
13.9 12.7 1.2 26.1 19.6 18.4 2.4 1.6 4.1 60.7
3.2 3.2 6.5 19.4 3.2 6.5 12.9 22.6 22.6 50.9
4.5 12.0 3.0 18.0 9.0 9.0 9.8 10.5 24.1 30.4
8.0 2.0 8.0 6.0 6.0 4.0 26.0 16.0 24.0 55.9
12.5 7.9 9.2 6.6 3.9 10.5 9.9 17.1 22.4 22.7
3.1 3.5 5.2 13.6 16.1 20.3 12.6 14.0 11.5 25.6
11.1 11.1 4.0 18.5 12.5 13.8 6.4 8.3 14.3 14.0
alnteractions initiated by first letter group, e.g. LM =low-rank animal initiates interaction with medium-rank animal. b X-= 15.5, P < 0.05: Z2= 20.1, P < 0.01, e.g. for X2= 48.3 groomings between rank groups are significantly different ( P < 0 . 0 1 )
20
J,D. KABUGA
DISCUSSION
It is clear from the present results that the supplementary feeding provided post-grazing was for a large part responsible for the high level of aggression during the feeding period observed. There were 1.4 times as many agonistic interactions during the F than NF. Agonistic behaviours were also highest during the first 30 min of observation when feed was available. It is also unlikely that a limited feeding space accounted for a significant part of the high level of aggression. Animals were provided with 62 cm of trough space per cow and this conforms to the 60-70 cm manger space per animal recommended for cows larger than the present experimental animals (British Standards Institute, 1979 ). Furthermore, these troughs were wide enough to allow animals to eat simultaneously on both sides of the trough. These results thus parallel previous studies which observed that supplementary feeding provided at only one locality and for a limited time of day results in competition and increased aggression (Metz, 1983). These data therefore suggest that there is no advantage in post-grazing feeding with a view to reducing the level of aggression at the feed troughs. This may not necessarily be so. It is likely that pre-grazing feeding would have resulted in a higher level of aggression than observed here because animals would be hungrier leading to more competition and aggression (Craig, 1981 ; Metz, 1983 ). The contribution of butting to the total number of agonistic interactions declined from 79% during the first 30 min to 68% during the second 30 rain in the F, as compared to about 60% throughout the NF (Fig. 1 (A) and 1 (B)). This high level of butting in both periods is contrary to reports that in wellestablished cow groups threats and passive avoidance are the main patterns of aggressive behaviour used to maintain social rank (Hafez and Bouissou, 1975 ). These animals were from a single herd so one would have expected a well-established hierarchy. Furthermore, common rearing experience and family relationships of some members of the group should have resulted in lower levels of aggression due to mutual tolerance (Bouissou and Andrieu, 1978; Reinhardt and Reinhardt, 1981). These results are, however, not unique. Kabuga et al. ( 1991 ) had previously reported the aggressiveness of N'dama cows even under grazing conditions. It is also apparent from the investigation that feeding elicited mostly agonistic behaviours and very little affiliative behaviours. However, immediately post-feeding the level of affiliative behaviours increased sharply above levels observed in the NF. One could speculate that animals were mending cohesive bonds disrupted or disturbed during the period of food competition. This speculation has some support from the high correlation between amicable behaviours initiated and received only in the F. The preferential butting of the sides by animals is consistent with the suggestion (Hafez and Bouissou, 1975 ) that this generally elicits flight and sub-
SOCIAL INTERACTIONS IN N'DAMA COWS
21
mission. However, the preferential butting of the sides and rear when animals were eating with their heads deep in the trough lead to some interesting questions concerning individual recognition with respect to dominant-subordinate relationships. Either these animals were able to identify conspecifics from the rear or sides or else other means such as olfactory cues (Syme and Syme, 1979 ) were used under these conditions. An unexpected finding in this trial was the lack of seasonal influence on the level of agonistic behaviours during feeding. One would have predicted that because of the poorer quality and quantity of forage in the dry season animals would be more hungry, resulting in more competition and aggression in the dry season compared with the rainy season. It may be that there is an optim u m level of aggression beyond which there may be no benefit in feed intake to the emitter of aggression. Alternatively, mutual aggression in this study may have reached a stable level (Metz, 1983) in the group before the investigation started. This experiment was initiated 6 months after supplementary feeding was introduced into the main herd. Cows initiated more grooming but not sniffing and rubbing in the rainy season compared with the dry season (Table 1 ). Grooming serves the function of removing noxious substances (faeces, urine and m u d ) and ectoparasites from the skin (Hafez and Bouissou, 1975). Since mud and ectoparasites are more prevalent in the rainy season, animals probably solicited and received more grooming from conspecifics. The l-year observation of the herd allowed us an insight into the nature of social dominance. Observations showed that at any particular time agonistic interactions were uni-directional, suggesting stability in the dominance hierarchy. However, over the l-year period there were some reversals in dominance ranks, as observed from reversals in agonistic interactions in 3% out of 435 dyads. Dominance was found to be complex rather than linear, despite the strong positive correlation of age and liveweight with number of animals dominated (Schein and Fohrman, 1955; Bouissou, 1972 ). This may have been due to the similarity of age and therefore physique and experience of some herd members (Syme and Syme, 1979). Some changes in rank were caused by illness and weight loss due to lactation. An interesting example was cow number 9 which, 7 months after the start of the trial, dropped from the first to the third position in rank when she calved and had a retained placenta. However, by the end of the investigation she was back to the second position in rank. These results are, therefore, at variance with results of previous studies which showed that in cattle herds rankings once established are very stable (Schein and Fohrman, 1955; Bouissou, 1972 ). Differences between our study and these results may be due to differences in the breed of cows used. In these studies Bos taurus dairy breeds were used. In this investigation there was a lack of significant relationship between dominance ranks and amicable behaviours such as grooming, in contrast to
22
J.D, KABUGA
other studies (Hafez and Bouissou, 1975; Hart, 1985 ). The lack of relationship in the present trial was probably the result of family relationships in the herd. Some young cows in the L group were daughters of cows in the H group but received most of their grooming from their mothers. ACKNOWLEDGEMENTS
The authors wishes to thank the management of the Boadi Dairy/Beef Cattle Research Station for providing facilities for the experiment, P. Yawkpe, Owusu-Ansah, D. Akumsa and my sons Collin and Mike for their help with observations, and Gladys A. Ndziba for typing the manuscript. REFERENCES Arnold, G.W. and Grassia, A., 1982/1983. Social interactions amongst beef cows competing for food. Appl. Anim. Ethol., 9: 239-252. Bouissou, M.F., 1972. Influence of bodyweight and presence of horns on social rank in domestic cattle. Anim. Behav., 20: 474-477, Bouissou, M.F. and Andrieu, S., 1978. Establissement des relations preferentielles chez les bovins domestiques. Behaviour, 54:148-157. British Standards Institute, 1979. For the Design of Buildings and Structures for Agriculture, Part II, Code 5502, p. 11. Craig, J.V., 1981. Domestic Animal Behaviour. Prentice-Hall, Englewood Cliffs, N J, pp. 145195. Hafez, E.S.E. and Bouissou, M.F., 1975. The behaviour of cattle. In: E.S.E. Hafez (Editor), The Behaviour of Domestic Animals. Bailliere, Tindall and Cox, London, pp. 203-245. Hart, B.L., 1985. The Behaviour of Domestic Animals. W.H. Freeman, New York, pp. 55-74. Kabuga, J.D. and Alhassan, W.S., 1981. Reproductive performance of Canadian Holsteins in the Tropics. World Rev. Anim. Prod., 17: 41-48. Kabuga, J.D., Gari-Kwaku, J. and Annor, S.Y., 1991. Social status and its relationship to maintenance behaviour in a herd of N'dama and West African Shorthorn cattle. Appl. Anita. Behav. Sci., 31: 169-181. Leaver, J.D., 1985. Milk production from grazed temperate grassland. J. Dairy Res., 52: 313344. Metz, J.H.M., 1983. Food competition in cattle. In: S.H. Baxter, M.R. Baxter and J.A.D. MacCormack (Editors), Farm Animal Housing and Welfare. Martinus Nijhoff, The Hague, pp. 164-170. Reinhardt, V. and Reinhardt, A., 1981. Cohesive relationships in a cattle herd (Bos indicus). Behaviour, 77: 121-151. Schein, M.W. and Fohrman, M.H., 1955. Social dominance relationships in a herd of dairy cattle. Br. J. Anim. Behav., 3: 45-55. Siegel, S., 1956. Non-Parametric Statistics for the Behavioural Sciences. McGraw-Hill, New York. Steel, R.G.D. and Torrie, J.H., 1960. Principles and Procedures of Statistics. McGraw-Hill, New York. Syme, G.J. and Syme, L.A., 1979. Social Structure in Farm Animals. Elsevier, New York, pp. 45-56. Wagnon, K.A., 1965. Social Dominance in Range Cows and its Effect on Supplemental Feeding. California Agricultural Experimental Station, Bulletin no. 819, University of California, Davis, USA.