Prevalence and Etiology of Subclinical Mastitis in Small Ruminants of Tigray Regional State, North Ethiopia

A study was conducted at Kafta Humera and Tanqua Abergelle Districts from April to June, 2011 to assess the prevalence of subclinical mastitis in lactating small ruminants and identify bacterial causative agents. A total of 390 lactating animals comprising 255 goats and 135 sheep were randomly selected from population and screened for evidence of subclinical mastitis. The overall prevalence of subclinical mastitis was found to be 18.03% (46/255) and 28.14% (38/135) in goats and sheep, respectively. California mastitis test (CMT) positive milk samples were subjected to bacteriological examination and the following bacteria were isolated; coagulase negative Staphylococcus (44.7%), Staphylococcus aureus (27.7%), Escherchia coli (17.0%) and streptococci (10.63%). Risk factors; species (p = 0.021), study site (p < 0.001), sheep breed (p = 0.018) and goat breed (p = 0.009) showed statistically significant association with the occurrence of subclinical mastitis in small dairy ruminants. However, there was no statistically significant association between risk factors such as Age (p = 0.779), parity (p = 0.201) and stage of lactation (p = 0.952). Therefore, it can be concluded that mastitis is a significant disease in small ruminants that affects their productivity and measures need to be taken to control the disease.


Introduction
Though small ruminant production is playing an important role in the improvement of Small ruminant (sheep and goats) rearing the incomes for poor farmers, poverty and hunger provide vast range of products and services such alleviation and can contribute a major role in the as immediate cash income, meat, milk, skin, country developmental plan, small ruminant manure, risk spreading/ management and social production and productivity and producers' functions (Adane and Girma, 2008) for poor benefits are far below expectations due diseases, farmers in many parts of Ethiopia.Small malnutrition, low genetic potential and poor ruminants with their higher reproductive capacity management practices.Among others infectious and growth rates are ideally suited to production diseases are the major constraints to small by resource-poor smallholders (Tibbo, 2006).
ruminant production in Ethiopia (Getahun, 2008; According to a recent report by Central Statistics Gizaw et al., 2010).Among these diseases Authority of Ethiopia, there are about 26.1 mastitis is one of the important diseases affecting million and 21.7 million sheep and goats' the productivity of small ruminants.population heads in Ethiopia, respectively (CSA, The nutritional components that make milk 2008).The small ruminant population of Tigray an important part of the human diet also support Region of north Ethiopia is estimated to be the growth of pathogenic microorganisms 1,022,779 sheep and 1,588,779 goats (TBoARD, coming from milk contamination or from animal 2006).
infections (Santos et al., 2009).The major district the sheep and goat population is about income of dairy sheep and goats comes from milk 65,108 and 85,073, respectively (TBoARD, production, which is mainly processed into 2006).fermented products and cheese.Thus, factors Study Design and sampling strategy: A cross influencing milk quantity and quality, such as sectional study was conducted to assess the subclinical mastitis, have an overwhelming effect prevalence of subclinical mastitis in small on economic losses to the farmer.In recent ruminants (sheep and goat).A total of 390 studies it was demonstrated that curd yield and its lactating, Begait and Abergelle breeds of goats properties were damaged by subclinical mastitis and sheep were included in the study.The sample as well, thus posing a secondary loss to the dairy size for the current study was determined industry (Leitner et al., 2004a, b).Compared to according to the formula given by Thrustfield, clinical mastitis, the subclinical form has major (2005) for cross-sectional, random sampling economic significance as this form of the disease method.A 5% absolute precision and 95% level doesn't manifest clinical symptoms (Quinn et al., of confidence was used for determining the 2002).sample size.An expected prevalence of 20% was In Ethiopia, there is paucity of literature used to determine the maximum sample size.dealing with the prevalence of small ruminant Accordingly, the sample size was calculated to be mastitis.Only few studies reported the prevalence 245 for each species however, a total of 255 of the disease in the country (Assefa et al., 2006; lactating sheep and 135 lactating goats were Megersa et al., 2009); making information available included in this investigation.on the prevalence of the disease and associated economic loss inadequate.However, sheep and California Mastitis Test (CMT): The California goat milk is routinely consumed by the rural and mastitis test was conducted to diagnose the semi-urban societies of Ethiopia next to the cow's presence of subclinical mastitis.This screening milk.This gap of information is higher in Tigray test was performed according to the procedure region in spite of the existence of huge number of given for mastitis by Quinn et al. (2002).The sheep and goats of different breeds; and this result was scored as 0, +1, +2 or +3 depending on limitation can pave a good opportunity for the the intensity of reaction.Samples with CMT transmission of different zoonotic diseases from result score of 0 and +1 were considered as animals to humans.Thus, the present study is negative, while those with score of +2 or +3 were designed to assess the prevalence of subclinical taken as positive.If at least one quarter was mastitis in small ruminants (lactating goats and positive by the CMT the lactating goat or sheep sheep), to determine the association of risk was considered positive.factors with the occurrence of subclinical mastitis Milk sample collection: Milk samples were and to isolate and identify the major bacterial collected aseptically from quarter's diagnosed causative agents of subclinical mastitis.
with CMT > +2 and were submitted for

Materials and Methods
bacteriological examination.Briefly, the udder of the goat/sheep was thoroughly washed with Study Area: This study was conducted on water and dried with clean towel.After lactating Begayt and Abergelle sheep and goats breeds of Kafta Humera and Tanqua Abergelle disinfecting the teats with 70% ethyl alcohol districts, respectively.Tanqua Abergelle District swabs, milk was collected.The first 3-4 streams is located in the central zone of Tigray regional of milk were discarded and then 5-10 ml of milk state while Kafta Humera is located in Western was collected from each teat aseptically in zone of Tigray Region of Northern Ethiopia.The separate universal bottles held a slightly horizontal total sheep and goats population in Tanqua position in order to avoid contamination from the Abergelle district is estimated about 264,596 and udder (Singh et al., 2007) determined as the proportion of affected Bacteriological examination was done on a total sheep/goat out of the total examined.These data of 23 goat and 24 sheep CMT positive milk were analyzed using Statistical analysis system samples collected from the study sites according (SAS) version 5 statistical software.To answer to Quinn et al. (2002).A loopful of milk sample the question of whether or not there is a significant was streaked on tryptose blood agar base association between all the risk factors, we enriched with 7% defibrinated sheep blood 2 conducted chi-square (χ ) test using the cross (Oxoid, UK) and MacConkey agar (Oxoid, UK) tabulation feature of the software.Logistic plates using the quadrant streaking method.Both regression analysis and odds ratio (OR) was done agar plates were incubated aerobically at 37 °C to see the strength of association.P < 0.05 was for 24 -48 h and examined for characteristic taken as statistically significant.bacterial colonies.Pure culture colonies were

Results
selected and sub cultured on general purpose medium, nutrient agar (Oxoid, UK), and Prevalence of Subclinical Mastitis: The 390 incubated aerobically at 37 °C for 24 -48 h for sampled animals from the two study sites for the further biochemical identification.After this current study comprise 255 lactating goats and incubation on nutrient agar (Oxoid, UK), bacteria 135 sheep.Out of this population, 46/255 were identified according to their Gram reaction (18.0%) goats and 38/135 (28.1%) sheep showed and morphology.Further identification of the CMT test positivity.Detail information of the organisms was done by implementing CMT result of the overall sampled animals from biochemical tests, Catalase, Oxidase, CAMP test, the two study sites is indicated in Table 1 were taken in to consideration to see the Structured data handling format was prepared integration with the occurrence of subclinical and every important information (variable) mastitis in the different species and breeds of the associated with the overall objective of the lactating small ruminants of the two study sites.investigation was properly gathered and Among the risk factors; species (p = 0.021), study recorded.Age, breed, parity, site and length of site (p < 0.001), sheep breed (p = 0.018), goat lactation were recorded.Age of the study animals breed (p = 0.009) showed statistically significant was recorded from the owners' information and association with the occurrence of subclinical

Table-1. CMT results of milk samples of sheep and goats collected from Kafta Humera and Tanqua-Abergelle
Prevalence and Etiology of Subclinical Mastitis in Small Ruminants of Tigray Regional State, North Ethiopia mastitis in small dairy ruminants.Accordingly, Staphylococcus aureus (27.7%),E. coli (17.0%), higher rate of prevalence was recorded in ovines and the least isolated bacteria were streptococci than caprines, Kafta Humera than Tanquawith prevalence of 10.6% (Table 3).

Discussion
Abergelle breeds.However, there was no Small ruminant mastitis is an important statistically significant association between risk disease that affects the productivity of the sector.factors such as age (p = 0.779), parity (p = 0.201) Inflammation of the mammary gland (mastitis) in and stage of lactation (p = 0.952).Table 2 sheep is predominantly subclinical (Contreras et summarizes the association of the different risk al., 1997).The occurrence of clinical and factors with the occurrence of subclinical mastitis subclinical mastitis in the different breeds of in small dairy ruminants.
sheep has been investigated in various parts of the Relative occurrence of bacterial isolates: The world (Al- Majali et al., 2003).standard primary and secondary bacterial The prevalence of subclinical mastitis in identification procedures conducted on the CMT goats (18.0%) reported in this study is in close positive milk samples of dairy goats and sheep agreement with previous findings of Megersa et has revealed the isolation of four common bacterial al. (2009) who reported 15.5% prevalence in organisms.Coagulase negative staphylococcus Borana, South Ethiopia.However, the present (CNS) were the most prevalent pathogens with finding in goats is lower than the prevalence prevalence rates of 44.7% followed by reported by other workers in Ethiopia (40.9% by The present study showed for the significant 2004b).Staphylococcus aureus is the second prevalence of the disease which has a significant predominant isolate in our study and Same is impact in the production of small ruminants.recorded by Beheshti et al. (2010) in Iran.The Thus, they do require good attention and presence of coliform mastitis (E.coli) could management practices to control or prevent the probably be due to poor hygienic conditions, as occurrence of the disease.The proper isolation these organisms originate from the animals and identification of the causative organism plays environment and infect the udder via the teat a significant role in the prevention and control of canal (Quinn et al., 2002).the disease.Further and detailed epidemiological In this study, ewes were more affected with studies should be conducted to determine the subclinical mastitis than caprines.This great prevalence of the disease at regional and national difference in the prevalence of the disease could levels.Additionally, studies on antibiotic be due to species variation which can lead to susceptibility tests should be done to determine difference in their resistance and susceptibility to the effective drug that can be used for successful mastitis.In goats, there are shorter (or even no) treatment of the disease.dry period (Bergonier et al., 2003); the teat of (Oltenacu et al., 1999)245, respectively while in Kafta Humera properly and transported on ice to Veterinary Microbiology laboratory in Mekelle University, dentition characteristics(Oltenacu et al., 1999).
Bacteriological examination of milk samples:

Association of Risk Factors with the Occurrence of reduction
. IMViC tests, Triple sugar iron agar test, Nitrate and Urease test.In addition mannitol Subclinical Mastitis: During the study period, salt agar was used to differentiate S. aureus from certain potential risk factors such as study site, coagulase negative Staphylococcus spp.age, species, breed, parity and length of lactation

Table - 3.The relative prevalence rates of various bacteria isolated from subclinical mastitis of goats and sheep.
Beheshti et al. (2010))Oromia Region) and disease in Kafta Humera can be explained by the Tanzania (e.g.51.5% by Swai et al.(2008), fact that the very hot environment in this area can 76.7% byMibilu et al. (2007)).According to the interfere with the immune defense mechanism of current investigation, the a total prevalence of the host which increases the susceptibility of the subclinical mastitis in lactating sheep was found animals.tobe28.1% and this is in close agreement withIn the present study, age, parity, and stage of the results reported in other countries of the world lactation didn't show statistically significant like 23.1% in Scotland byBerriatua et al. (2001)association with the occurrence of subclinical and it is significantly higher than 9.23% mastitis.However,Beheshti et al. (2010)in Iran prevalence reported byBeheshti et al. (2010)in reported a significant (P < 0.05) relationship with Iran.These variations could be as a result of the age and prevalence of subclinical mastitis where variations in the breed, husbandry of the animals there was higher rate of occurrence in old and multiparous ewes than young and primiparous and agroclimatical conditions.ewes.The absence of statistically significant Coagulase negative staphylococcus was the variation with the occurrence of the diseases and most predominant isolate in our study which these risk factors in these study sites could be accounted for about 47.7% of the bacterial explained by the husbandry factors where all isolates.This finding is in accordance with the animals are reared together and hence equal risks literature and previous reports(Adwan etal., for exposure.2005; Bergonier et al., 2003; Leitner et al.,