Materials and methods

Study areas

This study was conducted in South Omo Zone, which is found in the Southern Nations Nationalities and Peoples Regional State (SNNPR) and situated in the southern part of Ethiopia (Figure 1). The capital of South Omo Zone, Jinka, is 750 km south of the capital city of the country (Addis Ababa). The zone has a total area of 2,241,731.598 ha. The majority of the land is fertile and cultivated, with trees and bushes covering the remaining area. The zone falls in the arid and semi-arid category of the agroecological zone. Chickens are the most important animals for South Omo Zone pastoralists and agropastoralists next to ruminant animals (Tesfahun, Kebede, & Effa, 2017).

This study was conducted in three randomly selected pastoral and agropastoral districts (Bena Tsemay, Hamer and Male) of the eight districts found in the zone. Moreover, nine sampling sites (kebeles), three from each sampled district were selected based on the chicken population size data (Table 1). Two to three chicken were randomly selected for measurement from each randomly selected household within each kebele.

Study ecotypes

In literature, chicken populations of the current study area were generally classified as Konso chicken ecotypes (Dana, Dessie, Waaij, & Arendonk, 2010). However, during the classification, samples were not taken from areas near the current study areas. Moreover, the results of our short pilot survey in South Omo Zone hinted at the presence of unique local chicken populations, which are different from Konso and were not described before. Furthermore, the studied chicken genetic resources are indigenous/local, producing, reproducing and surviving under the local environment since many years.

Data collection

The FAO guidelines for animal genetic resource characterization (FAO, 2012) were used to set the overall data collection procedures including the male to female ratio within the sampled chickens. The sampled chickens were randomly selected from flocks of representative households. Eleven qualitative traits (feather morphology and distribution, head shape, comb type and size, body shape, and colours of plumage body, earlobe, skin, shank, and eye), and six quantitative measurements (wingspan, body length, chest circumference, shank length, shank circumference, and live body weight) (Table 2) were recorded from 303 adult chicken (95 cocks and 208 hens) under the effect of district and sex.

During the measurements, animals were carefully handled by trained laborers and made to stand properly with parallel legs. The measurements were carried out by two researchers – one measuring and one recording data. At the same time, two other researchers handled the qualitative data recording. To minimize subjective error, all the measurements were taken by the same researcher throughout the study. Quantitative measurements were taken early in the morning before the animals were fed and watered using textile tape measures. Body weight was taken using sensitive digital weighing balances to the nearest of 0.05 g.

Quantitative measurements

Level of significance (P values) outputs for the effect of district and sex on the quantitative measurements analyzed for the chicken populations as a whole and separately for each sex are presented in Table 3. Results of the overall analysis show a significant effect of sex on the studied traits with dominance of cocks on all measured traits. Similarly, all studied traits were affected significantly by district in the sex-aggregated analysis. However, effect of district on wingspan and shank circumference was variable due to individuals’ sex, where the cocks’ wingspan and the hens’ shank circumference were not significantly different across districts.

Least square means with the respective standard errors (LSM±SE) for the effect of district on the quantitative measurements of the chicken populations as a whole and separately for each sex are presented in Table 4. Cocks from Hamer district have the lowest values except for wingspan, while their counterparts from Bena Tsemay and Male districts were not significantly different in the measured traits. Body length, chest circumference, shank length and body weight of the Hamer hens were also lower than their counterparts from the other districts.

Qualitative characteristics

The hypothesis whether the qualitative characteristics of the studied chicken populations differ across districts and sexes was tested using chi-squared analysis. The results presented in Table 5 showed a significant effect of district and sex on most of the qualitative characteristics. The colour-related traits except earlobe colour of the cocks were significantly affected by district.

The percentages of qualitative characteristics in each district are presented in Table 6 and Table 7. Accordingly, silky feather morphology was observed on Bena Tsemay cocks. The majority of Bena Tsemay cocks possess single comb while one-fourth of the Male and Hamer cocks have a double comb type. The rectangular body shape was observed on almost half of the Bena Tsemay cocks, while the triangular body shape was dominant on cocks from other districts. All Hamer hens possess triangular body shapes while one-fourth of the Bena Tsemay hens had rectangular body shapes. The majority of the studied chicken populations have been characterized by normal feather morphology and distribution, plain plumage pattern, flat head shape, single comb type, and triangular body shape. The comb size of the studied chicken populations was sex-dependent; the majority of hens had small combs while cocks had medium-sized combs. The spur was also absent in the majority of hens from all districts.

Red plumage, earlobe and eye colour combined with yellow skin and shank colour, were dominantly observed in cocks from all districts (Table 7). On the other hand, red earlobe and eye colour with yellow shank colour were observed in the majority of hens in all districts. The majority of chickens in the Bena Tsemay and Male districts had yellow shank colour, while chicken populations from Hamer district had a large proportion with grey shank colour. Similarly, the skin colour of most of the chicken population from this study were yellow and white, with grey skin colour observed only in Hamer hens (18.6%). The plumage body colour of Male and Hamer hens was dominated by grey colour while brown, red and black were observed in the majority of Bena Tsemay hens.

Multivariate analysis for discrimination of chicken populations

Quantitative measurements

The quantitative measurements taken have produced reliable information on characterization, evaluation and differentiation of the studied chicken populations. In line with most reports, these measurements were significantly affected by the location sampled. The longest wings and smallest body size of the Hamer chickens make them significantly different from the chicken populations of the other two locations. These long wings stretched from the small body size can be recorded and reported as the unique characteristics of Hamer chickens, which might be related to their mothering ability.

A previous study by Dana et al. (2010) which describes Konso as a chicken ecotype took only two quantitative measurements (the body weight and shank length). In terms of body weight both cocks and hens of the current study were heavier than the Konso chicken ecotype where the body weights of the Konso cocks and hens were 1,411 g and 1,011 g respectively (Dana et al., 2010). Such phenotypic variations in body weight hint at the presence of genetic diversity that needs to be conserved and can also be used as a base in attaining genetic improvement through selection. Therefore, in terms of body weight, the current chicken populations were different from the Konso chicken ecotype.

On the other hand, their shank length measurements were comparable. According to Melesse et al. (2011), the shank length is considered a good indicator of adaptation to lowland areas and skeletal development, which is related to the amount of meat a chicken can carry. This shows their high adaptability to the lowland areas of the pastoral and agropastoral community.

Comparable, higher and lower values of wingspan, body length, chest circumference, shank length and shank circumference measurements were reported in indigenous chickens in different parts of the country. However, surprisingly low values were also reported. For example, Negassa, Melesse, and Banerjee (2014) reported 7.35–8.17 cm of wingspan and 22.6–24.2 cm of body length for chickens in southeastern Ethiopia. Similarly, Halima, Neser, Marle-Koster, Dekock, and A (2007) reported 12.67–15.83 cm of wingspan and 0.53–0.93 cm of shank circumference for chickens in northern Ethiopia.

Effect of sex

Cocks were bigger and heavier than hens, which follows Rensch’s rule (Rensch, 1950) where the males of an individual species are generally larger than the females. Such differences between cocks and hens may be attributed to the differences in hormone secretion, which leads to enlargement of muscle mass and skeletal development (Baneh & Hafezian, 2009). These results were in line with the reports of Bekele, Kebede, Ameha, and N (2015), Getu, Alemayehu, and Wuletaw (2014), Negassa et al. (2014), and Melesse et al. (2011), Dana et al. (2010) and Halima et al. (2007) on different indigenous chicken populations of Ethiopia. Similarly, sexual dimorphism was reported for most traits with males having higher values when compared to the females in other species of Ethiopia, including goats (Mustefa et al., 2019), cattle ( Mustefa et al., (2020b)), donkeys ( Mustefa et al., (2020a)) and sheep (Hailu et al., 2020).

Qualitative characteristics

Observable qualitative characteristics, in addition to the quantitative measurements, have allowed us to characterize, identify and differentiate the studied chicken populations. Dana et al. (2010), Bekele et al. (2015), Melesse et al. (2011) reported normal feather morphology and distribution in the majority of indigenous chicken populations in Ethiopia’s southern region that are comparable with the results of the current study. Melesse (2000) described the naked-neck gene as one of the main genes responsible for heat tolerance of some Ethiopian indigenous chicken populations by improving and enhancing heat dissipation due to the reduction in feather coverage. However, the current study also revealed the adaptation of indigenous chickens to the local pastoral and agropastoral lowland areas with a lower frequency of naked-neck chickens. This lower frequency of naked-neck chicken in the current study area specifically, as well as in the country in general, may also be a factor for their poor productivity (Ajang, Prijono, & Smith, 1993). Similarly, Yunis and Cahaner (1999) reported the probability of attaining higher egg and/or meat production in chicken with reduced feathering due to the saved feather protein.

Qualitative deviations were also observed between Konso ecotype and the current chicken populations. Firstly, the comb types, which vary greatly depending on the breed, are also a great indicator of a chicken’s health. Bright fleshy combs indicate physical strength and good health. Combs also help chickens regulate their body temperature – those with large combs are able to circulate blood faster through their combs, which helps to release body heat. This is why chickens adapted to warm environments have larger combs (like single combs and buttercup combs) while breeds from colder areas have smaller combs (like pea and rose combs) (Vaughn, 2019). The majority of chickens from the current study area were single-combed while Dana et al. (2010) reported a higher frequency of pea-combed chickens in the Konso chicken ecotype. Dana et al. (2010) also reported humid lowland to wet highland ecological zones as local areas of the Konso chicken ecotype. The comb size of the studied chicken populations was found to be sex-dependent where hens of a given population had smaller combs than the cocks. This was supported by Bell (2002) who reported the association of comb size with gonadal development and intensity of light.

The earlobe colour of a chicken can determine the colour of the egg that it will lay. For example, if the chicken has a red earlobe, it will lay a brown-shelled egg and if it has a white earlobe, it will lay a white-shelled egg (Bell, 2002). Red earlobe colour was observed in the majority of chickens from the current study, while Dana et al. (2010) reported equal frequency of red and white earlobe colours in Konso chicken ecotype. The observation of a higher proportion of hens with white earlobe colour than the cocks in each district was due to the sex-linked nature of the trait (Luo et al., 2018). Among the populations of the current study, a higher proportion of white earlobes was observed in Hamer hens than the others, which might be due to their distinction from the others as earlobe colour is a breed-specific trait, though it could also be affected by the nutritional status of the chicken populations (Melesse et al., 2011).

The triangular body shape was dominantly found in the current study while the results of Dana et al. (2010) reported blocky body shape for the majority of the Konso chicken ecotype. On the other hand, similar qualitative characteristics, like flat head shape, were observed on both Konso chicken ecotypes (Dana et al., 2010) and the current chicken populations.

Chicken populations, breeds and breeding groups can be identified by their plumage colours due to their decorative qualities. Plumage colour is also a key trait during the interaction of chickens due to their well-developed visual perception of the world (Makarova, Mitrofanova, Vakhrameev, & Dementeva, 2019). In agreement with most Ethiopian reports, several plumage colours were found in the current study area with a higher frequency of red-coloured cocks. On the other hand, the predominance of grey (faded white and black) colour observed in hens is in line with the reports of Halima et al. (2007). The diverse plumage colours in the current study, which might be due to either genetic or environmental factors, showed the presence of diverse genetic resources, which can be an input in conservation and genetic improvement programmes for sustainable use.

Bekele et al. (2015), Getu et al. (2014), Halima et al. (2007), Dana et al. (2010) reported yellow as the most widespread shank and skin colour in different indigenous chicken populations of Ethiopia, which agrees with the current findings. According to Hammond and Harshaw (1941), a chicken’s shank and skin colour are influenced by breed, quantity of xanthophyll pigment in the diet, and quantity of a pigmentation-suppressing factor in the diet. Bell (2002) stated that yellow shank colour is due to nutritional carotenoid colourants in the epidermis when the melanic pigment is absent. Similarly, variable shades of black colour are the result of melanic pigment in the dermis and epidermis; if the black colourant is in the dermis and yellow in the epidermis, greenish shanks will appear. However, if both these pigments are completely absent, the shanks will be white (Bell, 2002).

Commonly, red, yellow and black eye colours are due to the three pigments in the form of hemoglobin, carotenoids and melanin respectively. Red eye colour is influenced by the degree of iridic vessels injection and hemoglobin content of the blood (Nelson, 1947). According to Nelson (1947), when chickens suffer from general anemia, a smaller amount of red colouration will be noted due to loss of blood volume. Therefore, the dominant red eye colour observed in the current study is a confirmation that these chicken populations were free from such suffering. As per the same author, continual egg production can decrease the yellow factor in eye colour. Therefore, the yellow eye colour chicken from Bena Tsemay district (27%) might indicate restrictions in egg productivity.

Multivariate analysis

The use of more quantitative measurements during the discrimination analysis approaches the results towards reality. This is supported by the current results, where only one quantitative measurement in hens had low discriminatory power.

In line with reports by (Mustefa et al., 2020) on Raya cattle (61%) and Hailu et al. (2020) on Tigray sheep (66%), the discriminant function analysis allowed the classification of an average 61% of the studied individuals into their respective locations. The observed highest classifications of individuals into their respective districts in Hamer cocks and hens (75% and 77% respectively) showed their distinctness from the others due to the unique characteristics they possess. However, the lowest classifications (45% and 53%) were recorded in hens from Bena Tsemay and Male district indicating strong similarities between them.

The highly significant and longest pairwise Mahalanobis distances between districts indicate the accuracy of the calculations and the distinctness of the populations from each other in a measurable group difference for the considered quantitative measurements. Accordingly, the longest distances of Hamer chickens from the other two chicken populations in this study showed its distinctness.

In conclusion, the main contribution of this diversity study is the provision of information and data for breed differentiation, conservation and sustainable utilization of the chicken ecotypes in the districts, as well as the collation of information and data available on chicken ecotypes of Ethiopia. Accordingly, the chicken populations can be categorized phenotypically into two groups: the Hamer group and the Omo group (which includes the indigenous chicken populations from Bena Tsemay and Male districts). However, such differences in phenotypic performances might be either due to genetic or environmental variations. Therefore, we cannot conclude that the differences are solely due to genetic variations. Thus, genetic characterization is recommended to understand their potential and the within- and among-population genetic diversity and population structures.

Data availability

As baseline data for further research and development work, these data will be made available in the country’s focal institute for indigenous animal genetic resources, the Ethiopian Biodiversity Institute (EBI) and the global Domestic Animal Diversity Information System (DAD-IS) databases.