Ž .
Production of meat was also affected by the social hierarchy Table 7 . Middle-rank- Ž
. ing goats produced more meat adding the weight of all their breedings per birth
Ž .
Ž .
5615.6 kgrgoat , followed from a distance by the high-ranking goats 4575.0 kgrgoat , Ž
. and finally those of lower rank 4236.1 kgrgoat . Similar results were observed in
1-month-old suckling kids, with the kids of the middle-status goats again weighing more Ž
. Ž
. 13729.2 kgrgoat , followed by those of uppermost rank 12035.0 kgrgoat , and finally
Ž .
those lowest in the hierarchy 10384.7 kgrgoat . Though the middle-ranking goats also have the greatest number of kids per birth, the difference is not significant.
4. Discussion
4.1. Social hierarchy in the herd This investigation clearly demonstrated the existence of a dominance–subordination
relationship in the social organization of the domestic goat and confirmed the observa- Ž
. Ž
. Ž
. tions of Marincowitz 1968 , Pretorius 1970 , and Addison and Baker 1982 . This
hierarchy was quite stable, the animals maintaining their position throughout the months, though there are always some animals that experience slight changes of position within
the herd.
Ž Some investigators Dickson et al., 1967; Bouissou, 1970, 1971, 1972, 1980, in cows;
. Ewbank and Meese, 1971, Reinhardt, 1985; Reinhardt and Flood, 1983, in bisons have
pointed out how the dominance–subordination relationships established between two animals are very stable, most of them persisting for several years, although very
infrequently, some of them may be reversed.
The hierarchic order has been observed to be linear, though not perfectly so, with an absolutely dominant animal and an absolutely dominated one. A significant result in the
Appleby test indicates that dominance is transitive more often than would be expected by chance. Of all the relationships obtained from the individual dyads, 92 were
consistent with the assumption of a linear dominance hierarchy, with only 8 reversals, generally in individuals dominating another of similar, though slightly higher, rank.
Ž .
Ž .
Similarly, Egerton 1962 , in American bison, and Alados and Escos 1992 , in Dama gazelles, obtained 5.5 reversals.
4.2. Aggression–dominance relationship The term aggressive behaviour, in the narrow sense, is reserved for behaviour that
Ž .
could cause physical injury to another animal Hart, 1985 . Antagonistic interactions between two animals engaged in establishing and maintaining their mutual dominance–
Ž .
subordinance status includes an array of actions Kondo and Hurnik, 1990 . The primary role of aggression in natural environments is to assure an adequate supply of scarce
Ž resources to animals with high status when competing with their own kind Craig,
. 1981 .
It has commonly been suggested that a function of ‘‘dominance’’ is to reduce Ž
. aggression within the group Rowell, 1974; Gauthereaux, 1978; Syme and Syme, 1979 ,
Ž because aggression consumes energy and increases physical harm to animals Syme and
. Syme, 1979 . To establish its position in the hierarchy an animal has aggressive
interaction with other members of the group, but once this position has been established, it is maintained for the most part without any need for physical confrontation, although
Ž .
reinforcement by physical threat, feint or butt is still necessary Canali et al., 1986 . However, even in stable groups, the dominance hierarchy does not prevent aggression
Ž .
Syme, 1974; Eccles and Shackleton, 1986; Alados and Escos, 1992 . In our study, the relationship between the social rank and rate of antagonistic
interaction initiated was positive, while it was negative with the rate of antagonistic interaction received. This indicates that higher-ranking animals constantly reinforce their
status by means of continuous aggression. This correlation between dominance position Ž
and aggression has already been described Beilharz et al., 1966; Reinhardt, 1980; Reinhardt and Reinhardt, 1975; Reinhardt et al., 1987; Collis, 1976; Orgeur et al., 1990,
. Wierenga, 1990; Alados and Escos, 1994 .
Several factors may have caused an increase in aggressive interactions in this study. Ž .
Ž .
1 The acquisition by the shepherd of a small herd 35 head which he added to the previous herd; the introduction of strange individuals to an established group usually
causes a disruption of the group’s social structure, resulting in an increase of ant- Ž
. agonistic behavior Brantas, 1968; Brakel and Leis, 1976; Barash, 1977 .
Ž . 2 Goats were forced to feed simultaneously from the same limited amount of food
Ž and space, which evidently led to a high degree of competition Brouns and Edwards,
. 1994 .
Ž . 3 Goats were overcrowded in too small a stable, so that the individual animals did
Ž .
not have enough room. According to Bouissou 1981 , high levels of aggression among domestic animals may reflect the high stocking rates of modern intensive husbandry
systems. Ž .
4 Milking was done in the stable with consequent disputes between the individuals to be milked.
This fact is reinforced by the significant increase in antagonistic behaviour of the Ž
. animals while in the stable 48 of interactions compared to during shepherding
Ž .
24.5 . These results point out the importance of the shepherd’s management in the welfare and production of the animals. Rarely in these poor areas is the owner of a herd
able to make an important investment in the enclosure or development system. The animals are crowded together in old stables lacking the necessary space and sanitation,
their grazing is supplemented in an insufficient number of feeding places, and they are milked in the same place where they rest. All this provokes more interaction than what
there might be with the consequent risk of injury to the animals and reduction in
Ž .
production e.g., growth rate, milk production, etc. . In fact, it has been suggested that the housing conditions of the animals are adapted to man rather than to the animals
Ž .
Ross, 1960 . It has been assumed that there is little direct or interference competition for food
Ž .
within groups of grazing herbivores Kiley-Worthington, 1978; Wittenberger, 1981 . Ž
Nevertheless, various authors Shank, 1972; Leuthold, 1977; Syme and Syme, 1979;
Bouissou, 1980, 1981; Addison and Baker, 1982; Arnold and Grassia, 1983; Metz, 1983; Reinhardt and Flood, 1983; Wierenga, 1984; Kondo and Hurnik, 1990; Brouns
. and Edwards, 1994 have observed that if an important resource, such as water, feed, or
resting space becomes restricted, animals engage in physical forms of antagonistic interaction more than if the same resources are freely available.
4.3. Influence of physical characteristics on social rank Among the problems that emerge from the study of social dominance in domestic
Ž .
animals, the effect of the individual characteristics age, size, horns has received much Ž
attention, since they strongly influence ranks within a herd Bouissou, 1972, Syme and .
Syme, 1979 . The oldest and biggest goats occupy the highest positions in the social ranking. Age
andror weight are positively correlated with social dominance in numerous ungulate Ž
projects Scott, 1948; Ross and Scott, 1949; Schein and Forhman, 1955; Collias, 1956; Mchugh, 1958; Espmark, 1964; Bouissou, 1964, 1972, 1980; Candland and Bloomquist,
1965; Beilharz et al., 1966; Dickson et al., 1967; Marincowitz, 1968; Pretorius, 1970; Ozaga, 1972; Tyler, 1972; Clutton-Brock et al., 1976, 1982; Stricklin et al., 1980; Arave
and Albright, 1981; Townsend and Bailey, 1981; Alados, 1983; Alados and Escos, 1992; Hall, 1983; Kilgour and Dalton, 1984; Reinhardt, 1985; Barrette and Vandal, 1986;
Rutberg, 1986; Thouless and Guinness, 1986; Lott and Galland, 1987; Bartos et al.,
. Ž
1988; Enoksson, 1988; Locati and Lovari, 1991 . However, some authors Collis, 1976; .
Lott, 1979; Eccles and Shackleton, 1986 have found no correlation. Thouless and Ž
. Guinness 1986 suggest that many of these studies have looked at too small a number
of individuals and included immature animals, invalidating the effects of age and weight.
Horns are very important in establishing a higher social rank. Because of this, the six goats with horns were between the first and seventh positions of the hierarchic order of
the herd in our study. Horn and antler length have been correlated with social status in Ž
. goats Ross and Scott, 1949; Collias, 1956; Hafez and Scott, 1962; Kolb, 1971 ,
Ž .
Ž mountain sheep Geist, 1966, 1971 , cervids Espmark, 1964; Geist, 1966; Lincoln et al.,
. Ž
1970; Kucera, 1978; Clutton-Brock, 1982, Barrette and Vandal, 1986 , chamois Locati .
Ž .
and Lovari, 1991 , and cows Bouissou, 1972 . However, other authors have not
Ž obtained these results Eccles and Shackleton, 1986, for big horn sheep, Rutberg, 1986,
. bison cows; Alados and Escos, 1992, or Dama gazelles .
4.4. Effect of dominance on feeding Ž
The cost of living in society includes competition for food Alexander, 1974;
. Kiley-Worthington, 1978 . This is made evident by the animals’ interference with each
Ž .
Ž other during shepherding Wilson, 1975 . Various investigators Dittus, 1977; Lincoln,
. 1972; Ekman and Askenmo, 1984; Brouns and Edwards, 1994 have observed that
feeding is strongly related to the social rank of the individual, and the dominant Ž
. individual is the one with access to a resource food .
Ž .
It has been known for years Davies, 1925; Jones, 1933; Stapledon, 1934 that the number of palatable species influences the degree of selectivity during shepherding.
Selection of shrubs and grasses was influenced by rank at the beginning of both spring and summer. In these seasons, there is a greater offer of forage, since rains and
temperatures are the most appropriate for plant growth. March 1987 was exceptional, possibly because of the extreme drought of the previous months, leaving scant forbs in
the field.
Ž .
According to Schoener 1971 , an animal must adapt its feeding habits the best it can Ž
. to adjust to a particular environment. Vivas and Saether 1987 point out that when the
nutritive value of the plants diminishes, the animal has two options for covering its energy requirements: it can either increase the intake of food or it can reduce the cost of
collection. It seems that abundance causes herbivores to tend towards specialization Ž
. Pyke et al., 1977 . When this abundance diminishes, ungulates widen their rank,
Ž consuming less-preferred plants Macarthur and Pianka, 1966; Schoener, 1971; Emlen,
. 1973; Owen-Smith and Novellie, 1982; Belovsky, 1984 . It would therefore seem that
energy invested in competitive interference for food increases when the quality of this Ž
. food increases Shopland, 1987 .
In this study, the goats behaved as generalists in the months of less availability of Ž
. food autumn and winter , since it is more advantageous for them to collect all the
species they find. They do not dispute the most palatable, because this would spend more energy than that which the plant, normally of low nutritive value at this time of the
year, would provide. On the contrary, when the forage offer is much greater and of
Ž .
better quality spring and summer , the goats behave as specialists, becoming more selective of the food to be ingested, and the higher ranking goats interfering with
Ž .
Ž .
subordinates to obtain the most-preferred species shrubs . Barroso et al. 1995 also obtained that goats had a high preference for bushes.
Ž .
Thouless 1990 has identified two ways in which the feeding behavior of animals is Ž .
affected by the identity of neighbouring individuals: a They are more likely to move Ž .
away, and to stop feeding while doing so, if the neighbour is socially dominant. b They take fewer bites as the distance from dominant neighbours decreases. These results
suggest that for grazers under natural conditions a more passive form of interference may be important.
Ž .
These results coincide with those obtained by other authors. Alados 1986 and Ž
. Ž
. Alados and Escos 1987 found that the Iberian goat Capra pyrenaica was more
Ž .
selective when the plants were abundant spring , and less selective when plants were Ž
. Ž
. less available winter . A similar result was found by Owen-Smith and Novellie 1982
Ž .
with the kudu, Warrick and Krausman 1987 with the mountain ewe, and Vivas and Ž
. Ž
. Saether 1987 with the moose Alces alces .
4.5. Effect of dominance on production Direct physical injury is perhaps the least important consequence of farm-animal
Ž .
aggression Fraser and Rushen, 1987 . Aggressive behaviour can have profound effects Ž
. on physiology. Kelley 1980 observed a reduction in the immunity to diseases as
Ž consequence of aggressive interactions. Other authors Dantzer and Mormede, 1979;
. Siegel, 1980 have observed a reduction in productivity due to increased stress.
Ž Social rank had a clear effect on production of milk and of meat weight of suckling
. kids in the first day of life and at 1 month of life . However, and to the contrary of what
might otherwise be thought, it is not the most dominant goats that were the most productive, but those located in the middle positions. Intermediate-ranked goat may,
suffer from less social pressure than the animals of inferior status and, at the same time not have to exert energy in continual aggression to maintain its position as with the most
Ž .
dominant animals. This was also observed by Csermely and Wood-Gush 1990 , who noted that high-ranking sows spent more time defending the pile of food than actually
feeding. Ž
. Craig 1986 points out that when resources are limited, access is not gained in
proportion to rank. Another possible cause for the most dominant animals not being the best producers is that when the animals are fed in the manger, the high-ranking animals
Ž .
tend to defend a particular area the center
with a good supply of food while subordinate animals quickly grab food at the edges and move only when forced to do so
Ž .
Ž .
Csermely and Wood-Gush, 1986 . Similarly, Sherwin 1990 and Brouns and Edwards Ž
. 1994 obtained a significant negative correlation between rank in the hierarchy and
priority access to limited feed; animals higher in the hierarchy were occupied with the strong defense of their individual space under the crowded conditions. Because of this,
dominant goats spend time and energy in protecting their food supply such that their food intake is not always much greater than that of subordinates. Futhermore, Wierenga
Ž
. 1990 pointed out that when animals eat at the feeding rack, they regularly change
feeding places before all the food at the previous place has been consumed and that this kind of behavior is observed more often in high-ranking animals.
It must also be emphasized that, though there is no difference at birth in the weight of the suckling kids of higher and lower-ranking goats, there is a considerably higher
weight increase in the suckling kids of top-ranking mothers. Upon birth, there is only a 300-g difference, but by the first month of life, the dominant mother’s suckling kids
weigh 1700 g more than those of underlying mothers. The possible advantage of the dominant mother’s suckling kids over those of the lesser ranking mother’s would be, as
Ž .
Ž .
pointed out by Espmark 1964 and Geist 1982 , that the offspring may benefit from their mother’s rank in terms of avoiding being displaced by other adults.
Ž .
Some authors have obtained similar results. Pretorius 1970 when working with flocks of goats of varying body weights found that the submissive, lighter animals lost
an average of 8.3 body weight under conditions of a partially restricted feeding source. On the contrary, when the goats were regrouped into flocks of similar weight there was
Ž .
Ž .
a progressive recovery of this deficit. Marincowitz 1968 and Pretorius 1970 report a direct relationship between social rank and mohair production.
5. Conclusions
