Goats are important for livelihood of a large number of people in the third world especially to women, chil-dren, and the aged, who are the most vulnerable mem-bers of society in terms of undernourishment and poverty. Ethiopia possesses 17,000,000 goats and stands second in Africa and fourth in the world (FAO, 2012). In the eastern part of the Ethiopia goat is highly valued and reared mainly for meat and milk production which is playing an important role in the improvement of income of the poor farmers. However production is still faced by many constraints like infectious disease, scarcity of feed, high mortality rates, long marketing channels and lack of market information (Fikru and Gebeyew, 2015). Among the diseases, mastitis is considered to be one of the expensive diseases in terms of production losses (Mathew and Menon, 2008; Bard-han, 2013; Hayle et al., 2020). 

Mastitis is any inflammation of the mammary gland or udder and one of the most important economically devastating diseases of dairy animals affecting parti-cularly farmer in developing world (Bergonier and Berthelo, 2003). Subclinical form of the disease is imperative because it is 15 to 40 times more prevalent than the clinical form (Sawant et al., 2009). It adver-sely affects milk quality and constitutes a reservoir of microorganisms for long duration that can lead to infection of other animals (Assefa et al., 2014). The most common cause of subclinical mastitis in most herds or flocks is bacteria origin and other predis-posing factors (Persson et al., 2011). In Ethiopia, the most commonly reported bacterial agents of mastitis in goat are Staphylococcus aureus, Streptococcus spp., Corynebacterium spp., Escherchia coli and Micro-coccus spp (Assefa et al., 2006; Gebrewahid et al., 2012; Haftay et al., 2016). Among these bacteria, S. aureus have been implicated as the leading cause of subclinical mastitis (Haftay et al., 2016). Diagnosis of subclinical mastitis is based on the presence of inflammatory markers in the mastitis leads to changes of milk somatic cell count (SCC) as well as chemical characteristics of milk and microbiological isolation of the causative agent (Hristov et al., 2015). Indirect tests such as California Mastitis Test (CMT), White Side Test (WST) and SCC are commonly used both in cows and small ruminants. White Side Test (WST) is an indirect, easily applicable screening test for sub clini-cal mastitis in which 4% sodium hydroxide solution are used as reagent (Contreras et al., 2007). Treatment and control of mastitis technique used in does is those adapted from cattle and can be   udder infusion and systemic antibiotic administration. The major anti-biotics used for treatment of mastitis in Ethiopia include penicillins, streptomycins, gentamycin and oxytetracycline. However, recent studies in country showed that there was increased resistance of S. aureus isolated from mastitis goat to various antimicrobial (Abdi et al., 2018). The main control principles in-clude: sound husbandry practices and sanitation, post milking teat dip, treatment of mastitis during non-lactating period, and culling of chronically infected animals. Early diagnosis of mastitis with reliable tests facilitates successful treatment and control (Sharif et al., 2009).

Description of Study Area

This study was conducted in two purposively selected wored as and one administrative town of eastern Hararghe Zone namely Haramaya and Babile wored as, and Aweday town. Haramaya woreda is found in East Hararghe administrative zone of Oromia Regional state in Eastern Ethiopia. The study area has a latitude and longitude of 9°24′ N 42°01′ E and is found at an altitude of 1600-2100 meter above sea level (m.a.s.l.) with 64.5 relative humidity, is 511 km far from Addis Ababa. The woreda experience   short rainy season in February and long rainy season from July to Septem-ber. The annual rain fall of the areas ranges from 118-866 mm similarly the average monthly minimum and maximum temperature of the area is 9.4 and 24°C respectively. Mixed crop livestock farming is the pre-dominant production system in the rural area. The main livestock types kept in the in study area includes cattle, sheep, goat, camel, donkey and poultry. The total livestock population of Haramaya woreda is about, 101,290 cattle, 112,354 goat, 73,846 sheep, 631 camel and 3,328 equine species (HAOR, 2019).

Babbile woreda is found in eastern Hararghe zone of Oromia Regional State. It is located 31 km away from the town called Harar and about 557 km east from Addis Ababa, the capital city of Ethiopia. It lies between 8°9-9°23N latitude and 42°15- 42°53 E longitude and is characterized by semi-arid and arid climate with average annual rainfall of 410-800 mm and the annual temperature ranges from 24-28°C. It shares its border with Gursum from the north, Fedis from the west, Harari National Regional State from the north-west and Somalia National Regional State in the east, South and South West. The total land covers an area of 200,000 hectors with a human population of 100,003. The livestock population of the woreda com-prises about 76,161 cattle, 11,470 sheep, 20,644 goats, 7,393 donkeys, 15,430 camel and 21,114 poultry. Aweday town is located in the Eastern Hararghe Zone of the Oromia Region state of Ethiopia, which is about 10 kilometers far from the city of Harar and 30 km from Dire Dawa and 10 km from Haramaya university and also located at an altitude of 1600-2100 m.a.s.l between latitude 9°26 N and longitude 42°01 E. The mean annual rainfall is 870 mm with a range of 560-1260 mm, with 64.5 relative humidity and the mean maximum and minimum temperatures are 23°C and 9.25°C, respectively. The main livestock types kept in the area includes cattle, goat, sheep donkey and poul-try.  Local breeds goat is reared in and around the study area for meat and milk production mostly. Mixed crop livestock farming is the predominant production system in the rural area.

Study Animals and Management System

All lactating goats from selected district located in diverse geographical areas of eastern Hararghe zone Babille, Haramaya and Aweday town managed under deferent management system. Goats are often kept mixed with sheep during day and night with some possibility of keeping goats alone. The predominant goat breeds in the study area are Haraghe and Somali breeds, which are managed under intensive and exten-sive system. The number of goats per house hold varies considerably from two to over 20 animals per flock in some instance. Farmers who own more goats and sheep keep them in separate hose and feed /graze them while those who own few goats keep them in their own houses by tethering and feed chat left over and cut grass from field in some study. It is also common to find flocks in closed roof housed and open house. Whereas kids up to 3 months of age are sepa-rately kept around a homestead during the day time and housed separately in a specially constructed house with mud floor or may share house with people in some study area. Milking is practiced often once a day (in the morning and evening) by older woman and a single milker at a time. Milk is mainly used for household consumptions and regarded as useful for women in some study area.  For this study, the average number of flock size was used to categorize the size as large or small 

Study Design

A cross sectional study was conducted from May 2020 - September 2021 to determine the prevalence of subclinical mastitis in goats and their associated risk factor.

Sample Size Determination and Sampling

The sample size of lactating goats required for this study is determined according to the following formula described by Thrusfield, (2018).

n = (1.96)2 Pexp(1 - Pexp)

d2

Where,

n = sample size, 

p = expected prevalence and 

d = desired absolute precision at 95% Confidence level.

Thus at an expected prevalence of 50%, 5% desired absolute precision and 95% confidence level, the required sample size is calculated to be 384. One administration town and two woredas in zone namely Babile and Haramaya woredas, and Aweday town, purposively selected from 20 woredas and included in the present study. The study kebeles in the study woredas were selected using simple random sampling and goat owning households selected using systematic random sampling based. Households from selected woreda were included in the study based on the presence of at least two lactating goat & their willing-ness. The calculated sample size was proportionally allocated to the respective woreda based on the estimated total target population respectively 173 from Babbile, 121 from Haramaya and 90 from Aweday based on goat. Simple random sampling was consi-dered to select the animals when more than five lactating goat. The number of households to be selec-ted was determined by dividing each sample size to number of lactating does and putative biological and environmental factors believed to be associated with the epidemiology of mastitis were interviewed and recorded. These include individual animal identify-cation, age, stage of lactation, body conditions, housing, hygiene, service, feeding & vaccination previous masti-tis history, parity & flock size recorded accordingly.

Clinical examination of udder

Animals were individually identified and clinically examined. During clinical examinations, palpation of udder and visual observation of udder lesion, clinical mastitis, udder symmetry, and size were performed. Additionally, observation of milk consistency, color changes, and presence of grossly visible substances were carried out. Clinical mastitis was recognized by some pathological changes such as swelling, pain, redness, and heat in case of acute mastitis, whereas hardening of the udder, blockage of the teats, atrophy or fibrosis, and abscess formation was regarded as chronic mastitis. Does showing clinical mastitis were excluded from the study whereas does with subclinical mastitis were included to this study.

Questionnaire survey

One hundred fifty owners of the examined animals were interviewed using a semi-structured questionnaire format. The questionnaire has mainly focused on herd structure, flock type (mixed or other livestock), cleaning frequency, kid management, housing type, vaccination, milking technique, knowledge of goat mastitis, importance of mastitis, treatment and general information on production, reproduction were obtained using the questionnaire for each sampling frame.

Milk sample collection

Aseptic technique was adopted in all steps pertaining to milk samples collection from does with subclinical mastists. Sterile vials were utilized in samples collection. Cotton balls dripping in 70% alcohol were also used. Cooler with ice packs was used for storing samples. Paper towels and disinfectant were used for cleaning teats (Precious et al., 2018). Permanent ink for labeling. About 3 ml of WST positive milk samples were put a sterile universal bottle and transported on ice box to the Haramaya university microbiology laboratory with a minimum of delay for routine culture techniques.  

Laboratory Analysis of Milk Sample

White side test

This screening test was conducted according to the standard procedure recommended by Kehir et al., (2008). The test is performed by adding (1-2drops) of sodium hydroxide solution 0.4% to 5drops of cold milk on glass on black background and then stirring the mixture vigorously for 20 seconds and results were read. In positive reaction the milk was separate to water and shreds or flakes but in negative reaction the mixture remains uniformly opaque.

Bacteriological examination

Bacteriological examination was done on 89 WST positive milk samples according to Quinn et al. (2002). Briefly A loop full of milk sample streaked on blood agar base (Oxoid, UK) enriched with 5-10% defbrina-ted sheep blood using the quadrant streaking method and plates were incubated aerobically at 37 °C   for 24 - 48 h and examined for characteristic bacterial colonies. Presumptive colonies were selected and sub cultured on selective media (MSA) and incubated aerobically at 37 °C for 24 - 48 h for color change. Pure colony sub-cultured on nutrient agar (Oxoid, UK) were identified according to their Gram reaction and morphology. Yellow color on manitol salt agar, gram-positive, catalase-positive, were presumptively identi-fied as Staphylococci and subjected to coagulase test using rabbit plasma at four hours for grit of coagu-lation property (Quinn et al., 2002). 

a) Grams staining

Gram staining procedures - A colony from a 24 hour culture was emulsified in sterile distilled water and a thin smear was made on a grease free slide and was fixed by gently passing it through a flame. It was covered with crystal violet stain for 30-60 s and then the stain was washed off with slow running tap water and covered with Lugol‟s iodine for 30-60 s. The iodine was washed off with clean water and acetone alcohol was used to decolorize the smear for few seconds before washing with clean water. The smear was covered with safranin for 2 min, rinsed and air dried. The prepared slides were examined micro-scopically at 100x (oil immersion). Objective gram positive cocci (0.5 to 1.5 μm in diameter) that occurred singly and in pairs, tetrads, short chains and irregular grape-like clusters were suggestive of Staphylococcus species (Cheesbrough, 2000).

b) Manitol salt agar

The discrete colonies that confirmed by presence of clear zone of beta hemolysis were streaked on MSA plate and examined after 24-48 h incubation  at 37 0C and for growth of bacteria and change of color. The presence of growth and change of pH in the media (red to yellow color) regarded as presumptive identification of S.aureus. The incubated slant in nutrient agar was maintained for characterizing the isolates.

c) Catalase test

Catalase test was used to differentiate those bacteria that produce catalase, such as staphylococci from non-catalase producing bacteria such as streptococci. In this test clean slide and sterile inoculating loop were used. Small amount of organism from colony which incubated overnight was collected and placed onto the microscope slide. Then using a dropper–3% hydrogen peroxide (H2O2) dropped onto the organism on the microscope slide and observed for immediate bubble formation (O2 + water = bubbles). Positive reactions were evidenced by bubble formation (Barrow and Feltham, 2004).

d) Coagulase test

Test was used to identify S. aureus which produces the enzyme coagulase which causes plasma to clot by converting fibrinogen to fibrin. The slide test were used after plasma was prepared with normal saline 0.2ml in 1.8ml of saline water then 5 ml of diluted plasma added to test tube and 0.5ml of an 18-24 hour isolated colony of bacteria from nutrient broth added and incubated at 370C and checked at an interval of 1, 3 and 6 hours for coagulation. Test samples that failed to react after 6 hours were left over night at normal temperature and re-examined. A positive reaction was indicated by definite clot format (Cheesbrough, 2000).

Antimicrobial Susceptibility Test

Representative isolates were examined for their in vitro drug sensitivity. The pure isolates in nutrient agar were first cultured in nutrient broth for 48 hrs. The sensitivity discs (DIFCO, OXIDO) were placed in  inoculated Mueller Hinton agar and commercially prepared discs were placed on the plates and lightly pressed down to ensure the antibiotics disc in contact with the agar. Then incubate aerobically at 37oC and the Inhibition zone were measured after 24 - 48 hrs on average of diameter in millimeter (Barrow & Feltham, 2004). 

Commercially prepared disc used were: amoxicillin (5ug), ampciline (10ug), Gentmycine (10ug), Choloro-phenicol (5ug), Erythromycin (10ug), vancomycine (30ug) and Tetracycline (30ug) which they were avail-able in the market and subjected by owners and vete-rinarians in field (CLSI, 2015).

Data Management and Analysis 

The collected data was checked and stored in Micro-soft excel spread sheet until analysis. Both descriptive and analytic statistical analyses were performed using STATA Corp14 statistical software. Descriptive statis-tics involved frequency measurement and row per-centage of categories of each variable. Analytical statistics comprised both univariable and multivariable logistic regression analysis. 

Variables (host-related and environmental risk factors) were included in the univariable logistic regression analysis. Variables with a p-value <0.30 in the uni-variable analysis were incorporated in the multi-variable logistic regression analysis. A category of a variable is said to have a statistically significant asso-ciation with the CMT result (subclinical mastitis) when the obtained p-value is less than 5% (p < 0.05) or the 95% CI of the odds ratio didnt include one.

Demographic Characteristics Respondents 

Of the respondents (n = 150) participated in the study, 76 (51%) were from Haramaya, 50 (33%) from Aweday and 24 (16%) from Babile woreda. There were more female respondent in all age group than male respondent. Out of this 116 (76.7%) and 14 (23.7%) were male and female respectively with higher age above fifty years old. 

Most of the respondents education level had read and write 111 (71%) followed by elementary 32 (25%) and college level 7 (4%). Averagely Higher of number of and goats per household were observed in Aweday when compared to goats in Haramaya (Table 1).

Table 1: Demographic characteristics of participants.

Table 2: Over all prevalence of subclinical mastitis at animal levels and udder halve level.

Laboratory Results

Among 768 udder halves of 384 goats examined, a 7.8% (30/768) of the teats of does were blind, while 23.2% (89/384) of goats were positive for subclinical mastitis at 95% CI (0.192-0.27) and 21.8% (161/738) of teat were positive using WST below (Table 2).

Risk Factors

Univariate analysis

In the univariable logistic regression analysis among the potential putative risk factors age, body condition, lactation stage, origin, mixing with others, housing, frequency of manure removal and previous history of mastitis showed a statistically significant association with the proportion of subclinical mastitis (p < 0.05). 

Whereas, parity, farming, flock size, milking tech-nique, presence of wound and source of animal health service didnt show statistically significant association (p > 0.05) (Table 3 and 4).

Table 3: Univariate analysis of animal related risk factors for occurrence of subclinical mastitis.

Table a Reference; CI: Confidence interval; *Significant

Table 4: Univariate analysis of managmantal risk factors for occurrence of subclinical mastitis.

Table a Reference; CI: Confidence interval; *Significant

Multivariate analysis 

From eleven variables with categories p-value < 0.30 and entered in the multivariable analysis, Age, lacta-tion stage and origin of sampled goat were found to be significantly associated with the prevalence of SCM in the final multivariate analysis and found to be independent explanatory variably in does subclinical mastitis occurrence. Studied does between 3-4 age were at more risks for udder infections than those in other age group (OR=9.06; 95% CI= 2.24-36.60). Similarly, does in late lactation stage were about three times at more risk than animals does in early lactation stage (OR=2.52; 95% CI=1.21-5.24) and animals sampled from Aweday (OR=4.43; 95% CI= 1.37-14.38) had higher odds (about 4.4 times higher) of being subclinical mastitis positive than those sampled from Haramaya (Table 5).

Table 5: Multivariate analysis of risk factors associated with subclinical mastitis.

Table a Reference; CI: Confidence interval; *Significant

Bacterial Isolation

During the course of the study a total of 89 milk samples were collected from does with subclinical mastitis and cultured on blood agar media. Accor-dingly, growth of different groups of bacteria was observed in 78.6% (70/89) of milk samples. However, since the objective was to isolate S. aureus, further bacteriological tests were conducted by taking only those colonies presumptive of this species and leaving others. Of the total 89 examined goat milk samples, 33 (37.1%) were positive for S. aureus. Though the highest number of S. aureus were isolated from Babile goat milk (48.7%) followed by Aweday (29.4%) and Haramaya (25%), the prevalence of S. aureus from subclinical mastitis samples was not significant (p > 0.05) among these three study site (Table 6).

Table 6: Summary of bacterial culture results by origin of goats.

Antimicrobial Susceptibilities of Isolates

Almost all 33 S. aureus isolates were subjected to antibiotic susceptibility tests. Six different antibiotics were used in this test. In-vitro antimicrobial resistance pattern of S. aureus isolates to the six antibiotics has been investigated. S. aureus were found to be resistant to chloramphenicol (84.8%) vancomycine (87.9%) and ampicillin (81.8%). The isolate were also moderately resistant to amoxicillin (48.5%) and tetracycline (42.4%). S. aureus were found to be susceptible to gentamicin (75.8%) and erythromycin (72.7%) (Table 7).

Table 7: Antimicrobial sensitivity profile of Staphylococcus aureus strains (n = 33; #: Number).

In this study goat farming was found to be practiced small-scale farmer by both sexes. However there were more female 116 (77.3%) than male 34 (23.7%). This outcome was in agreement with result of Ogola et al. (2010) and Ngugna, (2017) who report that goat farming in Kenya was practiced by female than male farmer. However the current result was contrast with result of (Mbndyo et al., 2014; Fikru and Gebeyew, 2015; Gebreyowhens and Kumar, 2017) who report that goat farming was practiced by male than female farmer in eastern Ethiopia, Kenya and Nigeria. The reason why there was more female got farmer than male is due to the fact that goat was easily managed by female unlike cattle. Different age group was participating in goat farming in both sexes. However large proportion of respondents age (41.2%) was 41-50 and above fifty. This result was in agreement with Byaruhanga et al. (2017) who found similar age of respondents participate in goat farming. The study explained that goat production in the study area was a mature older aged business and suggested that older age farmers were engaged in goat farming. This could be attributed to the fact that tendering of the goats under tethering system, which was predominant in study area, requires less attention,  so, it was easier for older people to manage goats with this system. In this study the overall does level prevalence of subclinical mastitis was 23.2% (95% CI, 19-27). This finding was close agreement with the previous finding of other researchers (15.5%) in South Ethiopia (Megersa et al. 2010), 18.3% in North parts of Ethiopia (Gebrewahid et al., 2012) and 24% in Southern Ethiopia (Ahmed et al., 2019). However present finding were lower than another study reported in Oromiya region (40.9%) (Assefa et al., 2014), Kenya (61%) (Mbndyo et al., 2014) and Tanzania (51.5%) (Swai et al., 2001). The variation in prevalence with those result observed in other areas might be due to difference in diagnostic tools, management systems of study animal and as well as genetic variation in disease resistance among breeds and technical knowledge of the investigators. Goats aged > 2 - 4 years had higher prevalence (30. 81%) of subclinical mastitis compared with goats aged between 1-2 years and >4 with occurrence rates of 7.9% and 23.39%, respectively. Satirical analysis re-veal that there was significant association (p<0.05) which was in line with study of (Ameh and Tari, 2000; McDougall et al., 2002; Moroni et al., 2005). But in contrast with that of Gebrewahid et al. (2012).The increase in occurrence of mastitis with age may be due to the fact that older goats are long term caretakers that have stayed longer in the herd and have higher chance exposure to pathogenic infection. In the present study, there was positive association between the body condition of goats and prevalence of subclinical mastitis. This result was close agreement with report of (Koop et al., 2009; Megersa et al., 2010; Mungube et al. 2004) who prove that low body condition was the major risk factor for increased mastitis prevalence, but showed no statistically significance association. Lacttion stage was the major risk factor for increased mastitis prevalence and factor remained significant in the final model. This finding was in agreement with result of Miblu, (2007) and Moroni et al. (2005) who reported that early stage and later stage of lactation had more infection than mid stage of lactation. Never-theless there were contrast with finding of (Ndgwa et al., 2001; Gebrewahid et al., 2012; Mbindiyo et al., 2014) who found no association between occurrences of subclinical mastitis with lactation stag of doe. Higher prevalence during late stage of lactation could be linked to imbalance energy intake and decline immunity. High content of somatic cell in milk at late stage increase false positive in screening. In the pre-sent study, there was increasing prevalence of sub-clinical mastitis with increasing parity number of lactating goats which was in line with pervious study by (McDougall et al., 2002; Megersa et al., 2010; Gebrewahid et al., 2012). Nevertheless there were contrast with finding by (Ndgwa et al., 2001; Gebrewahid et al., 2012; Mbindiyo et al., 2014) who found no association between occurrences of suclinical mastitis with lactation stag of doe. This is credited due to the health care of does and parturition stress. Untreated case in the first parity takes natural course to chronic status possibility of carryover of infection from the first parity to the next may occur. In this study, goats that were sampled from Aweday had a higher prevalence of subclinical mastitis (37.8%) com-pared with goats sampled from Haramaya and Babbile with prevalence of 13.2% and 22.5% respectively. This increase occurrence in Aweday may be due to man-agement system. Since all the goats sampled from Aweday were kept in closed house and intensive management system where as goats sampled from Haramaya were smaller in size and good in hygienic standard when compared with the other locations from where the goats sampled. In this study prevalence of sub clinical mastitis were higher in does kept in closed house (30.17%) and does mixed with sheep (27.20%) when compared with studied does kept in open house (20.15%) and alone (14.63%) respectively. which was closed agreement with study result of  (Ndegwa et al., 2000; Megarsa et al., 2010; Aqib et al., 2018) who found high occurrence of sub clinical mastitis in studied animal in closed house with earth floor type and animal reared with sheep but showed no statis-tically significant association. This increase occurrence of subclinical mastitis in animal kept in closed house and animal mixed with other could be explained by the fact that  muddy wet earthen floors is a common finding in most closed housed and mixed rearing system which tends to harbor a wide range of infec-tious agents that may contaminate the udder and teats. In this study, there was significantly higher prevalence of mastitis in does whose houses were cleaned irre-gularly and weekly when compared to those whose house were cleaned more frequently but statistically not significant. These results were consistent with study result of (Bergonier et al., 2003; Mbindiyo et al., 2014; Precious et al., 2018). Current prevalence of S. aureus was 37.1% which was higher than the previous reports of (Molla et al., 2006; Gebrewahid et al., 2012) who report 12.8% and 27% prevalence in the southern and northern parts of Ethiopia. The high prevalence of S. aureus in this study might be associated with poor hygienic conditions were pathogens originate from does environment that infect the udder via the teat canal since dirty and wet bedding is a common earthen floors, tends to harbor a wide range of infectious agents that contaminate the udder and teats. The purpose of antimicrobial test is to generate information about which drug is effective against S. aureus causing goat subclinical mastitis in the study area. The eva-luation of the antimicrobial susceptibility S. aureus isolated from goats with subclinical mastitis to decide which antibiotics should be administered, as well as, for monitoring the spread of multiple resistant strains on farmhouses (Salvatore et al., 2010).

In this study isolated S. aureus showed high percent of antimicrobial resistance to chloramphenicol, vancomy-cine and ampicillin. These results were in line with the results of Haftay et al. (2016) who observed a re-sistivity of 100% to vancomycine, 90.9% to ampi-cillin in a study carried out in northern Ethiopia; and Onanuga et al., (2005) and Aqib et al., (2018) who also found a 100% and 70% resistance to chloram-phenicol in Southern Nigeria, and Pakistan respect-tively. However the present study was not concurs with earlier study by Teshome et al., (2015) who obtained S. aureus isolates were found to be resistant with tested antibiotics in the following percentage: chloramphenicol (10.5%), vancomycine (5.5%). The probable explanation to the presence of high antibiotic resistant by S. aureus to chloramphenicol and vanco-mycine may be due to indiscriminate and protracted/ repeated use of these antibiotics in human health and indiscriminate use of antibiotics by individual farmers without prescription of professionals in study area. S. aureus has been known to show multiple antimicrobial resistance patterns (Alian et al., 2012). The widespread use of antibiotics has undoubtedly accelerated the evolution of S. aureus, which as a result of the acqui-sition of multiple resistance genes has become able to survive almost all antibiotic families (Alian et al., 2012). In the present study S. aureus isolates also high susceptibility to erythromycin, gentamycin tetra-cycline and amoxicillin which was comparable with the results obtained by Tashom et al. (2013) who found S. aureus isolates sensitive for the tested anti-biotics in the following percentage: Erythromycin (78.9%), gentamycin 84.2%, tetracycline 56.2% and amoxicillin 57.9%. However, (Tofaily et al., 2011; Mekuria et al., 2013) found that the susceptibility rate of S. aureus isolates to Erythromycin was 21.6% and 16.6%. This might be that these antibiotics are not frequently used in the study area in veterinary services and possibly in human medicine. Studies show that susceptibility patterns of S aureus to antimicrobial agent have varied worldwide, but isolates were usually susceptible to gentamicin (Alian et al., 2012).

Subclinical mastitis of lactating does in eastern Har-arghe was encountered condition. S. aureus was a prevalent bacteria isolated from does with subclinical mastitis; this indicated that S. aureus was an important cause of subclinical mastitis. Risk factors, such as age, stage of lactation and the study site were responsible factors for the occurrence of subclinical mastitis in the study area. S. aureus isolates were developed resis-tance to various antimicrobial agents. Resistance to Vancomycin and chloramphenicol has been recorded in almost all S. aureus isolates and needs serious atten-tion. However S. aureus isolates were susceptible for erythromycin and gentamycin. These all findings may provide essential information on epidemiology of the disease and the causal agents to implementing an integrated prevention and control strategy of goat subclinical mastitis in the study area. 

The following recommendations are made based on the key findings of this study.   

 Additional investigations of other pathogens involved in goat mastitis will optimize our know-ledge of causative agents and control interven-tions

 Microbiological examination of udder of lactating goats at regular intervals should be routinely carried out in order to detect subclinical mastitis and underline course. 

 Judicious use of antibiotics may be included in designing in the prevention strategies against occurrence of SCM with antibacterial resistant isolates. 

 In-vivo antimicrobial susceptibility patterns of S. aureus isolates should do.

Ethical Approval

Ethical approval was obtained from the Institutional Research Ethics Review Committee (IHRERC) of Haramaya University, College of veterinary medicine   official letter of support was sent to SGS office and to other concerned bodies. This study was conducted in accordance with the Declaration

We are thankful to veterinary laboratory personnel and university authorities to the completion of the success-ful research study.

The authors declare that there is no conflict of interest.