Introduction

Bovine mastitis is a single most common disease syndrome in adult dairy cows, accounting for about 38% of morbidity (Smith, 1996). Mastitis is also associated with number of zoonotic diseases in which milk acts as a vehicle of infection (Jenkins, 1982)

Previous study on the prevalence of mastitis indicated 10% of cows in most farms in Ethiopia have at least one blind quarter (Goshu et al., 1985). A study conducted by Mohammed (1996), on bacterial cases of bovine mastitis in Zebu-Holstein dairy cows in Wondo-genet area also found a quarter infection rates of 16% by potentially pathogenic bacteria. The prevalence of bovine mastitis is higher in farms with larger herd sizes than in those with lower herd sizes (Radostits et al., 2000). The prevalence is also higher in cows with lesions and tick infestations on the skin, udders and teats than cows without these factors, in early lactation stage than in the mid-lactation stage (Biffa et al., 2005).

North Shewa is a high potential cereal-livestock zones where dairy activities play a significant role in the livelihood of farmers in the area. Considering the potential of the area and the economic significance of dairy production to the local community there have been repeated efforts by governmental and non-governmental aid organizations to improve the dairy productivity. This area has also better access to livestock development services (governmental and non-governmental) and milk markets than other rural areas. Due to the above mentioned reasons and the economic capacity of the peasants small-holder dairy production with crossbred dairy cattle is a common practice in the area. Conversely, bovine mastitis was reported to be one of the most prevalent dairy health problems in most parts of Ethiopia where dairy activities are practiced. Yet, the information on the prevalence of sub clinical mastitis in the area is lacking and what available is fragments of information from cases of clinical mastitis that has been presented to veterinary clinic for the treatment. This investigation was proposed to determine the prevalence of sub clinical mastitis and to isolate the dominant bacteria in the study area.

Materials and methods

Description of the study area

Selection of the study animals

Screening of the udder quarter for mastitis

Bacterial culture

Data analysis

Results

A total of 153 apparently health lactating cows were examined for sub clinical mastitis by using CMT and 137 (89.5 %) was found positive for mastitis. From 137 CMT positive animals, 122 were bacteriologically positive. Out of 612 quarters, 386 (63.1 %) were infected. All positive quarters milk samples were cultured and 90 % (347 of 386) yielded growth and in the remaining 10 % (39/386) there was no observation of growth (Table 1). The resulting quarter infection rate was 56.7 % (347/612). After culturing the following dominant isolates were found to be Staphylococcus epidermedius, Staphylococcus intermedius, Staphylococcus aureus, Microccocus, Staphylococcus hyius sub spp hyius respectively. Bacteria belonging to Staphylococcus genera were isolated with Staphylococcus epidermedius (38.4%), Staphylococcus intermedius (23.2 %) and Staphylococcus aureus (13 %) dominating the milk flora (Table 2).

Figure 1

Table 1: Mastitis in udder quarters of small holder dairy cows in Selale, North Shewa Zone, Central Ethiopia

Figure 2

Table 2: Frequency of microorganisms isolated from cows milk samples

Discussion

The prevalence of sub clinical mastitis 89.5 % in cow and 63.1 % quarters found in this study was higher than the prevalence (62.9 % and 33.74 %) reported by Kerro Dego and Tarek (2003) and Seyoum et al (2003), respectively. The difference in prevalence observed between the reports from different parts of Ethiopia and the present study may be due to differences in management and husbandry condition in the area and lack of awareness of farmers to the loss caused by mastitis.

Staphylococcus was the predominant organism isolated from the sub clinical mastitis and followed by Micrococcus, Streptococcus and other Gram positive rods in decreasing order. Similar organisms were isolated from cases of mastitis by other authors (Kerro Dego and Tarek 2003; Seyoum et al 2003). It is well established that Stapylococus species and many of the streptococcus species, inhabiting the udder and/or on the udder skin, cause contagious mastitis. The transmission of contagious mastitis from infected udder to health udder is through milker's hand during milking processes and possibly flies.

The present study showed high prevalence of sub clinical mastitis in cow in the study area. The isolated mastitis causing pathogens were many of which Staphylococcus, Micrococcus and Streptococcus are the major one. Further studies are required to identify risk factors for sub clinical mastitis and antibiotic sensitivity tests as this would help to devise treatment and control of sub clinical mastitis in dairy cow in the area.

Acknowledgements