HIERARCHY IN A GROUP OF DOMESTIC GOAT (CAPRA HIRCUS) FEMALES

Marcin Tadeusz Górecki

ABSTRACT

The study was carried out in the years 1998-2001 in Złotniki Experimental Farm. Observations included 82 female goats differentiated with respect to hornedness, age, breed and color. During the study period the animals were weighed seven times. The goats were observed in production conditions in groups arranged by goat-house workers. The number of animals in the observed groups was from 4 to 61. The same goats were observed in subsequent groups formed due to connecting and separating already existing groups. During the observation continuous recording was carried out. On basis of agonistic behavior for each individual a dominance index (di) was calculated being a quotient of the number of animals over which the individual dominates and the number of animals with which it enters into domination relationship.

Key words: domestic goat, Capra hircus, social hierarchy, hornedness..

INTRODUCTION

Domestic goat (Capra hircus) being an animal of great economic importance is a subject matter of numerous research studies. However, the number of ethological studies concerning the goat is relatively low, though this species has lively temper and wide range of behavior. The richness of behavior of domestic goat can be indicated by the fact that Schino [12] described reconciliation in domestic goats, previously noted only in Primates. Domestic goat are often kept in the conditions far different from the natural environment of their wild ancestors. Barroso et al. [2] found that social position of a goat affects its productivity. These observations point out to the need for studying social behavior of domestic goat, which would enrich ethological knowledge and can have practical value for goat breeders. The objective of this study was to check whether inter-individual relations in a group of domestic goat females are stable and to find out what factors affect social position of an individual.

MATERIAL AND METHODS

Observations were carried out in the Agricultural Experimental Farm in Złotniki near Poznań, Poland, from March 1998 to April 2001. The total number of female goats included was 82. The White Improved breed and crosses of the White Upgraded with Boer goat were observed. The age of the individuals at observation was from 6 months to 10 years. Both horned (n=52) and hornless (n=30) goats were observed. The color was from uniform white to completely brown. Also the partially colorful forms: brown head, patches, etc., were noted. Body weight of the animals depending on age and genotype was from 22 to 79 kg. During the observation period body weight was measured seven times: twice in Spring (April 1998 and May 2001), twice in Summer (July 1999 and 2000), twice in Autumn (September 2000 and November 1999) and once in Winter (January 2000). In Złotniki the goats are kept indoors: they never go out into a pasture, rarely use grassy yard.

A direct observation method was used. The same person made all observations and recorded (wrote down) them. One observation session lasted from 2 to 7 h. The total number of hours of observations was 580.Continuous recording [1] and sampling all occurrences of all social behavior and such which could have social importance was carried out. The observed animals were individually marked with numbers about 30 cm high painted on sides and rump with washable spray for animal marking. The observations were carried out in production conditions in technological groups arranged by workers of goat-house. The number of goats per group was from 4 to 61. The same goats were observed in subsequent groups formed due to connecting and dividing the already existing ones.

From observations of agonistic behavior, for each individual a dominance index (di) was calculated being a quotient of the number of individuals over which the observed one dominates in relation to the number of the animals with which it gets into domination relations. To determine the effect of the studied factors on the domination index, a variance analysis according to the method of the least squares was used as well as Pearson’s correlation to evaluate the effect of body weight on di, and Spearman’s rank correlation to assess relationships between hierarchical systems in each groups [11].

RESULTS

Most of the determined relationships among the investigated animals seems to be stable as proven by the level of Spearman’s rank correlations between hierarchical systems in each goat group. As many as 74% of the determined inter-relationships were statistically significant (p<0.05 and p<0.01) reaching the level of the coefficient r_S >0.6 (Table 1). In case of two-year-old and older goats hierarchy in groups after connection was always statistically highly significantly correlated with the social order before combining the groups (r_S from 0.86 to 0.95; p< 0.01), whereas among the two, observed before connection, groups of young goats (G3 and G7) only in one case it was correlated on a high level with the hierarchical system prior to connection (G3, r_S =0.96; p<0.01), and in the other case the relationship was not statistically significant (p>0.05).

In the years 1999-2001 several goats were observed in the herd which maintained a very high domination index (di>0.66). There were also goats which in 1999-2001 maintained a low domination index (di<0.33). Also changes in the di value were noted. For example, after combining groups G2 and G3 di of the goats from G2 increased while in those from G3 lowered. However, following some time spent in G6 di of the goats from G3 increased and that of the animals from G2 decreased. Several goats from G3 group took a permanent high positions in the herd hierarchy maintaining di>0.66 in later observed groups. Similarly, the cases of permanent fall in a goat’s position, e.g. after a disease were observed. Another example of changes in goat’s position in a herd is the animal N^o 18, which in 1999-2001 maintained di=1, with an exception of one period (Spring – Summer 2000) when its di was 0.91 since it surrendered to the goats ov er which it earlier and later dominated.

Hornedness were usually a factor affecting hierarchy in a statistically significant way (p <0.01). Only in the groups of goats of the same age (in the first and second years of life: G3,G5 and G7) it did not have this effect on hierarchy (p>0.05; Table 2). Mean di of the horned goats was higher also in these groups.

Body weight. Variance analysis revealed statistically significant effect of body weight on animal hierarchy only in four groups (Table 2), whereas Pearson’s correlation coefficients between body weight and domination index in as many as thirteen groups were positive and reached medium and high level (r_P from 0.49 to 0.82; p<0.05 and p<0.01; Table 3).

Age turned out to be a factor affecting animal hierarchy in a group. An exception were the groups G2 and G6. However, in these groups an increase in the mean value of di with age can be also observed.

Hair cover color turned out to be a statistically significant factor only in three investigated groups: G4, G8 and G9a (p<0.05). In all three cases the white goats had higher mean domination index.

Breed group (origin) did not turn out to be a statistically significant factor in any of the studied goat groups. Despite this, in three groups, the difference in the value of mean dominance index calculated for goats of various origins was high. In the group N^o4 the goats with admixture of Boer genotype had di higher than the remaining ones while in the groups G3 and G5 the opposite was true: higher di had the goats without admixture of Boer breed genotype.

The variance analysis determining the effect of the above mentioned experimental factors was very accurate as seen from the value of the determination coefficient. In the majority of analyzed groups R² exceeded 0.8.

DISCUSSION

Results of current study revealed existence of a clearly determined social hierarchy in domestic goat female group. Literature concerning returned to the wild and feral representatives of Capra genus usually does not describe social hierarchy among females [7, 14, 15]. An exception is the work by Husband and Davies [4] presenting hierarchy among females of wild goat (Capra aegagrus) observed, however, only in pens built by the observers. In the herds of domestic goats, on the contrary, the existence of herd hierarchy was noted [e.g.: 2, 6, 8, 10].

According to Hafez et al. [3] hierarchy in a goat herd remains stable for years. Barroso et al. [2] found stability of the hierarchy lasting for 18 months. My results confirm these observations: in the majority of cases Spearman’s correlation among hierarchical systems was strong and statistically highly significant, even if two years passed between observations of the groups.

Author’s own studies indicated in most cases a significant positive effect of horns possession on social position of an animal. Similarly Scott [13] and Ross and Scott [9] noted positive effect of horns on social position of a goat. Also Sambraus [10] observed that horns were the factor most strongly shaping position of an animal in observed goat herds.

In this research a statistically significant effect of body weight on hierarchy in a herd was observed: heavier goats had higher social position. Similar results were obtained by Pretorius [8] in an observed herd of angora breed females and by Keil and Sambraus [6] in two German herds of milk goats. According to Hafez et al. [3] and Barroso et al. [2] body size affects social position of a goat. On the other hand, Sambraus [10] found relationship between body weight and social position only in three from ten observed herds. The level of correlation between goat body weight and its social position was from r_P = 0.45 (p<0.05) to r_P =0.8 (p<0.01).

Results of this study indicated that the age of a goat is positively correlated with its social position. Scott [13] and Ross and Scott [9] obtained similar results. Also according to Hafez et al. [3] and Barroso et al. [2] older goats dominate over the younger ones. Whereas Sambraus [10] found statistically significant correlation between age and social position only in two from eight observed goat herds. In his studies one of the correlations was positive (r_P = 0.67; p<0.05), while the other one was negative (r_P = -0.73; p<0.05).

In this study no statistically significant effect of breed on animal social status was found. The hair color influenced the hierarchy in only three groups. No literature data was found on goat breed and hair color influence on hierarchy though the effect of animal breed on its social position was noted in other species, e.g. domestic pig [5].

The study was partially financed by a grant received from Polish State Committee for Scientific Research.

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