Morphological characterization of Arab and Oromo goats in northwestern Ethiopia: implications for community-based breeding programs

Background: An exploratory eld research was conducted in Northwestern Ethiopia, to characterize the morphological features of Arab and Oromo goat populations as a rst step to design breeding programs. Ten qualitative and nine quantitative traits were considered from 747 randomly selected goats. All data collected during the study period were analyzed using R statistical software, version 3.5.2, 2018. Results: Plain white coat color was predominantly observed in Arab goats (33.72%) while plain brown (deep and light) coat color was the most frequent in Oromo goats (27.81%). The morphometric measurements indicated that Oromo goats have signicantly (P < 0.001) higher body weight and linear body measurements than Arab goats. Positive, strong and highly signicant (P < 0.001) correlations were obtained between body weight and most of the body measurements in both goat populations. The highest correlation coecients of chest girth with body weight for Arab (r = 0.95) and Oromo (r = 0.92) goat populations demonstrated a strong association between these variables. Live body weight could be predicted with regression equations of y = -33.65 + 0.89x for Arab goats (R 2 = 90) and y = -37.55 + 0.94x for Oromo goats (R 2 = 85), where y and x are body weight and chest girth, respectively, in these goat types. Conclusions: The morphological variations obtained in this study could be complemented by performance data and molecular characterization using DNA markers to guide the overall goat conservation and formulation of appropriate breeding and selection strategies. and EL) to be signicant (p < 0.05) for Arab goats and ve parameters (CG, EL, CW, BL and HL) to be signicant (p < 0.05) for Oromo goats. In the present study, high coecient of determination (R 2 ) that ranged between 90–96% in Arab goats and 85– 86% in Oromo goats and low residual mean square (MSE) values between 2.11 to 5.00 in Arab goats and 2.72 to 3.04 in Oromo goats were recorded using the regression analyses.

crop-livestock and agro-pastoral (19). The Arab goats predominate in this district. The second study area, Bambasi district, is situated in the sub-humid agroecology and it is positioned at 9°45′ north latitude and 34° 44′ east longitude with an elevation of 1,668 masl (20). The mean annual rainfall ranges from 900-1,500 mm and the average temperature is 28 °C (21). A mixed crop-livestock system is the dominant production system (22). The Oromo goats are predominant in Bambasi district. Detailed description of the study areas is given in the previous work (16).

Data collection
A total of 747 goats (258 Arab and 489 Oromo goats) were sampled for both qualitative and quantitative measurements. The Arab goats were selected in Gumu-Abush, Sherkole, Tumet and Tsore-almetema villages of Homosha district whereas the Oromo goats were sampled in Bambasi 02, Mutsa 01, Shebora and Womba-selama villages of Bambasi district. The goats were classi ed into six age groups based on their dentition, i.e., kids (< 6 months), young (6-12 months), 1 pair of permanent incisors (1PPI) (1 year), 2PPI (2 years), 3PPI (3 years) and 4PPI (≥ 4 years) (23). The kids and young goats were differentiated by asking the age of goats from owners while the goats in 1, 2, 3 and 4 and above years were differentiated by observing their dentition. From the total sample size, 629 (84.2%) were female goats. The relatively high number of females could be attributed to the fact that they are normally retained in ocks by the goat keepers for reproduction while the males are more frequently put up for sale (16). Pregnant does were excluded from measurement to avoid over estimation of body weight (BW) and linear body measurements (LBMs). In the current study, quantitative traits, except BW, are generally named as LBMs.
Ten qualitative variables (coat color pattern, coat color type, head pro le, horn presence, horn shape, horn orientation, ear orientation, wattle presence, ruff presence and hair type) were recorded by using the standard format adapted from the (6) breed descriptor list.
Nine morphometric measurements were also taken on each goat in the morning before they were released for grazing. The measurements were taken as described by (6). They included body weight (BW), the fasted live body weight (in kg); chest girth (CG), circumference of the body (in cm) immediately behind the shoulder blades and perpendicular to the body axis; body length (BL), horizontal distance (in cm) from the point of shoulder to the pin bone; wither height (WH), vertical height (in cm) from the bottom of the front foot to the highest point of the shoulder; rump height (RH), vertical height from the bottom of the back foot to the highest point of the rump; chest width (CW), width (in cm) of the chest between the briskets; pelvic width (PW), horizontal distance (in cm) between the extreme lateral points of the hook bone of the pelvis; horn length (HL), length of the horn (in cm) on its exterior side from its root at the poll to the tip and ear length (EL), length (in cm) of the external ear from its root on the poll to the tip. Body weight (kg) was recorded using suspended spring balance. The height measurements (cm) were taken using a graduated measuring stick while the length, width and circumference measurements (cm) were measured with plastic measuring tape. All measurements were taken after restraining and holding the goats in their natural position and before they were released for grazing.

Statistical analyses
All the data collected during the study period were encoded and fed into MS-Excel (2010). Based on the nature of data, different types of statistical analyses were used. The qualitative data were analyzed using 'datasets package version 3.5.2' of R software (24). Chi-square (χ 2 ) test was carried out when required to assess the statistical signi cance among qualitative variables.
The quantitative data were analyzed using 'LSM (least squares mean) package version 3.5.2' of R (24). Tukey's comparison test was used to compare the sub factors that brought signi cant differences.
The statistical model used was: Where, Yijk = the values of BW and LBMs in the ith age, jth goat population; µ = overall mean; Ai = xed effect of ith age (i = < 6 months, 6-12 months, 1PPI, 2PPI, 3PPI and ≥ 4PPI); Gj = xed effect of jth goat population (j = Arab, Oromo); (A × G)ij = interaction effect of age with goat population; and eijk = effect of random residual error. Due to the fact that only a few male goats at older age classes (3PPI and ≥ 4PPI) were available in the study areas, male animals were excluded in the model in the analysis of BW and LBMs.
Pearson's correlation coe cient (r) values for the goat populations were also computed to assess the relationship between BW and LBM using 'cor.test function' of R (24). In addition, to estimate BW from LBMs, the maximum adjusted R 2 method of same software was used and stepwise regression procedures were implemented to screen out the best tted model using the 'MASS package version 7.3-51.1' of R (24). Furthermore, the 'model r package version 0.1.4' was used to calculate the MSE (mean square of error). In the rst step, all LBMs were entered together into the model for each goat population. Then, a group of variables having the maximum adjusted R 2 and minimum MSE were selected. In addition, Akaike's information criteria (AIC) and the Bayesian information criteria (BIC) were considered. In the second step, the variables which were selected by maximum adjusted R 2 and minimum MSE were entered together into the model to nd the best tted regression equation. Yi = β0 + β1 × 1 + β2 × 2 + β3 × 3 + β4 × 4 + β5 × 5 + β6 × 6 + β7 × 7 + β8 × 8 + ei Where, Yi = dependent variable (BW); β0 = intercept; X1,. . ., X8 = independent variables (CG, BL, WH, RH, CD, PW, HL and EL); β1,.. ., β8 = regression coe cients of the variables X1,. . ., X8; and ei = residual random error.

Qualitative characteristics
The frequency and percent of qualitative characteristics observed in male and female goats of the two populations are presented in Tables 1 and 2. The results of the study showed that plain, patchy and spotted coat color patterns were observed in both goat populations, with maximum incidence in Arab goats (66.28% plain) and minimum incidence in Oromo goats (9.41% spotted). Thirteen types of coat colors were observed in the sample goat populations, of which white in Arab (33.72%) and brown in Oromo (27.81%) goat populations were the most frequently observed coat colors followed by brown (16.67%) and white (21.27%) in Arab and Oromo goats, respectively (Fig. 2). Plain black coat color was less frequent than plain white, brown or gray ones. However, amongst the mixed goat coat colors, a mixture of white and black with white dominant is the predominant coat color observed in both goat populations.
Variations between the two goat populations were also observed in other qualitative characteristics. For instance, 61.63% of Arab and 95.5% of Oromo goats were characterized by straight head. The horned goats accounted for about 97.67% and 87.93% of Arab and Oromo goats, respectively. More    (Table 3). Highly signi cant (p < 0.001) differences were observed between the two goat populations in most of the studied quantitative measurements, except for horn length and ear length.

Age effect
The LSM for BW and LBMs were signi cantly (p < 0.01) in uenced by age groups. Except for age classes of 2PPI and 3PPI, there were signi cant increases in BW and other LBMs as the age increased from the youngest (kid) to the oldest (4PPI) age group (Table 3). Results clearly indicate that BW and LBMs increase proportionately with the advancement of age. This situation is however expected since the size and shape of animals change as the age increases. Maximum gain on BW and LBMs was observed between 6 to 12 months of age.
Interaction effect The   (Table 4)

Discussion
The current study was exclusively based on qualitative records and quantitative measurements to characterize and identify the morphological features of Arab and Oromo goat populations of Benishangul Gumuz region in northwestern Ethiopia.
Based on our results on the analysis of qualitative variables, the two goat populations have various coat color patterns and wide range of coat color types. This may be attributed to lack of systematic selection and would offer an opportunity for setting-up selection or breeding program in the study areas. However, the predominant coat colors and their patterns should be well included when goat improvement programs are designed. In addition, most of the qualitative traits were not in uenced by sex except horn absence and ruff presence which were mostly expressed in male goats. The higher proportion of polled males than females in both goat populations could be due to either goat keepers' high preference to polled male goats or high frequency of short-horned allele (HoP) in males. The present result agrees with (25) who reported higher number of polled males than females in western Ethiopian goats. However, horn presence is an advantage for thermoregulation (26; 27) and better reproductive performance (28; 29). Likewise, the presence of wattle is associated with thermoregulatory function, milk yield and reproductive performance such as higher proli cacy, litter size, fertility and conception rate (27) and higher body measurements (30). Therefore, the occurrence of horn and wattle would be used as selection criteria by goat keepers of the study areas for improved performance.
(31) reported that on the basis of wither height; adult goats can be classi ed as large (> 65 cm), small to medium (51-65 cm) and dwarf (< 50 cm).
According to the current results, both Arab and Oromo goats can be grouped under small to medium sized breeds. However, Oromo goats had signi cantly higher averages of BW and LBMs, showing that animals belonging to this population have better body conformation for meat production than animals in Arab goat population. Such difference was also observed in a study conducted by (12) on the same goat types in northwestern Ethiopia. The variation between these goat populations could arise due to difference in genetic characteristics and/or environmental conditions that may affect phenotypic variance (32). The relatively harsher environment, in terms of feed and water shortage and high environmental temperature, under which the Arab goats are raised could have been largely responsible for their lower body dimensions. Because these stress factors could have prevented the Arab goats from expressing their genetic potential. This is in line with what has been reported by (33). The authors documented that temporal and spatial variation in weather, plant productivity and subsequent nutrition could have major impacts on physical growth of animals. However, at the scope of the present study, it is di cult to associate body size, shape and conformation to any genetic background. Future studies could look in to genetic differences of the two goat populations. The coe cients of variation (CV) obtained for quantitative traits such as BW, CG, BL, WH, RH and HL were relatively higher. This could be due to absence of selection, or the body parts are affected more by the environment than others (34).
Investigation on the effect of age on quantitative measurements of goats indicated that BW and LBMs increase proportionately with the advancement of age. Similar ndings were reported by (15) for western lowland goats and (25) for goats found in western Ethiopia. However, the maximum body gain was observed between 6 months to 12 months. This may be due to natural increase in dry matter intake after the goats reached age at puberty.
(35) also found maximum body gain at 9 months of age for Rohilkhand goats in India. The current average body measurements of goats in different age classes are higher than previous ndings from similar age western lowland goats reported by (15).
The correlations among quantitative traits were generally positive and highly signi cant that ranged from 13-95% in Arab goats and 12-92% in Oromo goats with the highest correlation between BW and CG in both goat populations (r = 0.95 in Arab goats and 0.92 in Oromo goats). In agreement with this nding, several authors (13; 36; 37; 25; 38) reported the highest correlation between BW and CG for some Ethiopian goats. This speci es that CG could be the best trait in predicting BW and may be used as a selection criterion in the study areas.
The positive and signi cant correlations among quantitative traits obtained in this study indicated that both goat populations have harmonious body conformation, re ecting balanced physical growth. Furthermore, it shows that the traits are under the same genetic in uence due to additive genetic effect (39). This implies selection for one or more of these traits may consistently increase other traits that have positive association with the selected trait/s. In addition, selection of positively correlated traits would have paramount importance in designing breeding programs in that the selection will lead to signi cant improvement of body weight and other body measurements that are of economic importance (34).
The regression analyses of BW with LBMs in the present study identi ed seven traits in Arab and ve traits in Oromo goats to predict BW. Similarly, (25) found seven traits in female (R 2 = 83%) and ve traits in male (R 2 = 88%) to predict BW of western Ethiopian goats. (37) also reported ve traits to estimate BW of Woyto-Guji and Central Highland goats with R 2 values of 84% and 79%, respectively. Nevertheless, CG was found to be the most appropriate variable to explain more variation in both Arab (adjusted R 2 = 90%) and Oromo goat populations (adjusted R 2 = 85%). The high coe cients of determination (R 2 ) in the current study indicated the strong association and success of LBMs in describing more variation in BW. This may be helpful for local goat keepers to make selection and cull decisions as it can be relatively low cost, high accuracy and consistency (40). Body measurements in some cases can be more reliable than modern weighing machines as the latter can give biased results caused by gut fullness (41).
As shown in Table 5 In the study areas, where formal breed data recording schemes are not well established (16)

Conclusions
The morphological characterization of Arab and Oromo goats found in Benishangul Gumuz region of northwestern Ethiopia demonstrated phenotypic variations between the two goat populations. In addition, the goats in the study areas had shown different phenotypic characteristics with relative to western lowland goat breed. However, it would be useful to include performance data into characterization studies to understand which genotype has comparative advantage within an agroecological zone. Furthermore, an investigation on the molecular characterization using molecular markers like SNP will complement the results obtained from morphometric differentiation and also be helpful in high resolution characterization, conservation and formulation of breeding and selection strategies.

Declarations
Availability of data and materials All data generated or analyzed during the current study are available from the corresponding author on reasonable request.