Incidence and Associated Risk Actors of Heifer Mastitis in Dairy Farms at Mekelle Town, Northern Ethiopia

Introduction

Bovine mastitis is the most prevalent and costly disease, affecting dairy farms worldwide. The infection can progress to systematic diseases and fertility disorders. Besides the health disorders of the mammary gland, mastitis, can also cause significant losses in milk yield, alterations in its quality (impaired nutritive and technological properties of milk), economic losses from culling of the chronically infected cows and cost of veterinary treatment [1, 2, 3, 4, 5].

In Ethiopia, the total population of animals used for milk production is enormous. About 42 percent of the cattle populations are milk cows managed by the private sector and the indigenous cattle are of poor genetic potential and their productivity is low [6]. The largest proportion of the milk comes from these indigenous cattle while the exotic cattle and their crosses contribute small amount to the national output of milk and milk products [7].

In the livestock development policy to improve the per capita milk consumption, improvement of the genetic potential of the indigenous zebu through breeding with high-grade exotics will be included. According to Lemma, et al. [8], of the major diseases of crossbred cows in Addis Ababa milk shed, mastitis was the second most frequent disease next to reproductive diseases.

The prevalence of clinical and sub clinical mastitis in Ethiopia range from 1.2 to 21.5% and 19 to 46.6%, respectively [9, 10, 11, 12, 13, 14]. However, there is a lack of information on the status of heifer mastitis in the country. To date there are only few reports on the problem, as reported by Siraj, et al. [14] and Ashenafi [15] in two regions of the country.

Knowledge of when heifers become infected with different mastitis pathogens is a prerequisite for establishing control strategies. Furthermore, knowledge regarding the persistence of intra-mammary infections (IMI) with different pathogens is necessary to make decisions regarding antibiotic treatment. Thus, the present study was designed to assess the incidence of heifer mastitis and determine associated risk factors for heifer mastitis in dairy farms and identify the major causative agents of heifer mastitis in and around Mekelle town, Northern Ethiopia.

Discussion

This study has given a due attention to determine the incidence and its risk factor assessment for heifer mastitis. This study showed a higher incidence rate of mastitis in heifers with higher quarter’s bacterial infection with a subclinical type of mastitis. The overall incidence of heifer mastitis in the study is comparable to the reports done in Wolaita Sodo town by Ashenafi [15], 60.7%. However, it is higher than the reports by Pankey, et al. [20], 46% and much higher than the reports done in Ambo town, Central Ethiopia by Siraj, et al. [14], which was 20.6%. This may be due to variation in management practices, weather conditions, breeds of animals studied and other related factors.

Generally, in this study the incidence rate in subclinical mastitis is higher than clinical mastitis. This result agrees with Ashenafi [15]. Heifers have a lower incidence rate of clinical mastitis compared with cows [21]. The owners of small holder dairy farms in the study area were not well informed about the invisible loss from subclinical mastitis. Therefore, mastitis in primiparas can be economically detrimental for a farmers’ business.

In the present study, highest incidence of heifer mastitis was observed at calving followed by early lactation. This agrees with the results obtained by Ashenafi [15] (35.7%). It is higher than the results reported by Oliver and Sordilo [22] who showed that 19.7% of heifer mammary glands were infected at calving but lower than Fox, et al. [23] as many as 50% all mammary quarters in heifers may have IMI at first parturition.

It is also observed that the chance of negative quarters to remain negative for a relatively longer period is higher compared to positive quarters. The likelihood that a quarter not infected in the preceding month could remain negative in the subsequent month was about twice higher than the likelihood that an already infected gland could be free of infection. The results are suggestive evidences that the application of antibacterial agents before the expected date of calving could help to reduce the incidence of mastitis during the early lactation period. The application of antimicrobials approximately two months prepartum was reported to have reduced the incidence of intramammary infections by 59% and treatment in the third trimester generally reduced the occurrence of new prepartum intramammary infections and persisted up to calving with cure rates ranging from 80 to 100% for Staphylococci and Streptococci [24].

The incidence of heifer mastitis was significantly affected by tick infestation. Though, the presence of teat lesion was not statistically significant, it showed a higher proportion for risking heifer mastitis. This is comparable with a study conducted by Nibret, et al. [25] in multiparous 70% and 77.7% and Ashenafi [15] 84.6% and 88.9% for tick infestation and teat lesions, respectively. Tick bite on udder can cause skin irritation and localized inflammatory response, which can lead to secondary bacterial infection. Scabs on teats are also potential sources of S.aureus [26]. Animals with skin lesions on their teats and/or udder had a high prevalence of mastitis, possibly because of colonization of the lesion by pathogens. Mulei [27] found, in the Kiambu district of Kenya, that mammary gland quarters with teat lesions were 7.2 times more likely to have a positive CMT and 5.6 times more likely to have bacterial organisms isolated from them than those without any teat lesions.

The highest risk of mastitis in heifers was within the first 15 days of calving, but tends to decrease as the calving increases. Among the potential risk factors considered for a univariate logistic regression, tick infestation, udder wash, hand wash, previous mastitis problem, heifer milking practice and towel use had significant effect on the incidence of subclinical mastitis. The period around parturition is stressful and management factors might have more pronounced effects on primiparas than on multiparous cows. Thus, it is plausible that there are different risk factors in housing, milking and management in the period around parturition for primiparous cows compared to multiparous cows [28].

Coagulase-negative staphylococci (CNS) were the major pathogen isolated from the heifres quarters Open Access Journal of Veterinary Science & Research

followed by Staphylococcus aureus. This finding was higher when compared with reports of Siraj et al. [14] 21.4% and Ashenafi [15] 15.2%. However, it is closely agreed with the reports by Oliver, et al. [22] that suggested CNS were isolated about (50%) as predominant major pathogen. In addition, Bishi [10] was found CNS as the predominant species from urban and peri-urban production system in Ethiopia and Bolivia, respectively. The higher isolation rate of these organisms might be due to the wide ecological distribution inside the mammary gland and skin.

CNS have traditionally been considered as minor pathogens, especially in comparison with major pathogens. However, more recent studies propose that infections with CNS may cause more serious harm [29]. Their importance has increased, as CNS has become the predominant pathogens isolated from subclinical mastitis in several countries [30] showing the emergence of this neglected bacterial species as a threat for the dairy industry.

Because of frequent isolation of CNS in mastitis infections it is now considered as an important re- emerging mastitis pathogen. Mastitis causing CNS can serve as a reservoir of resistance genes that can be transferred to other bacteria such as, S. aureus. Importantly, this phenomenon increases the difficulties of controlling and/or treating against mastitis [4]. The prevalence of CNS mastitis is higher in primiparous cows than in older cows.

Staphylococcus aureus isolates were found to be the second most prevalent pathogen. The result is lower than the previous reports by Siraj, et al. [14] 27% and Ashenafi [15] 30.3%. In addition, it is much lower than the findings of Fox, et al. [23] that suggest Staphylococcuss aureus (44.3%) as a predominant pathogen. The results are comparable with other reports in Ethiopia in multiparous cows [31, 32]. Although the primary reservoir of _S.aureus_is infected quarter of lactating heifers and cows, this bacterium also colonizes teat skin, vagina, muzzle, and other body sites, but also bedding, feedstuff, air, equipment.

Staphylococcus aureus mastitis in dairy heifers can persist through the peripartum period and in to the first lactation. The resulting damage to developing mammary tissue can reduce milk production and cause the heifer to fail in reaching her maximum milk production potential.

S. agalactiae and S.dysagalactiae were the third prevalent genera; the result is much lower than the reports from other studies in Ethiopia Siraj, et al. [14] 12% and 6.1%; Ashenafi [15] 35.7% and 14.2% in primiparous cows [31, 32, 33]. The _Streptococcus_species cause problems during the post parturient period in heifers (Fox, 2009) [10]. Exposure to environmental streptococci may occur during milking, between milking and during dry period [34].

Enterobacter bovis and Klebsiella pneumonae were also ranked the same to Streptococci in the list of pathogens identified. Comparable results were reported from Siraj A, et al. [14] 3.6% and 6%, respectively but it is lower than the reports by Ashenafi K [15] 10% for Klebsiella pneumonae but were no isolate for Enterobacter bovis. The present study revealed that E. coli, S.agalactiae and S.aureus were highly incident at calving predominantly of S.aureus at calving were in agreement to previous reports by Owens et al., [26]. In addition, similar reports were reported in Ethiopia by Siraj, et al. [14] and Ashenafi [15]. The idea shared with Ashenafi the transmission pathways responsible for new S.aureus IMI occurring during the dry period may be similar to transmission pathways for prepartum heifers in that both groups of animals have similar environmental circumstances.

The other bacterial species were of lesser frequency and similar distribution patterns by previous workers in primiparous [14, 15]. In addition, similar reports were suggested by Lakew, et al. [32]; Bitew, et al. [31]; Mekbib, et al. [33] in multiparous cow in Ethiopia. The reason of variations in the preponderance of the bacterial species among the different studies could be due to management practices in farms and the agro-climatic heterogeneity of the country [23, 35].

In recent years, the use of integrated control measures has become paramount, due to the onset of resistance against the antibiotics commonly used to treat the disease. This is particularly relevant to the primary causal bacterium of bovine mastitis, Staphylococcus aureus. This study has summarized the risk of heifer mastitis for the dairy industry. Different risk factors are associated with its occurrence. In addition, certain neglected bacterial agents such has CNS has a paramount contribution for both the clinical and subclinical mastitis in heifers. An integrated approach between the animal health workers, farmers and stake holders should be directed toward the prevention and control of heifer mastitis in the region. Furthermore, a thorough study which encompasses the genetic aspects of the bacteria and host relationship should be conducted.

Open Access Journal of Veterinary Science & Research

Acknowledgment

This research was supported by the sub-thematic research projects "Impact of microbial Pathogens involved in pneumonia, diarrhea and mastitis on food safety, food security and international trade and development of assays" under the Thematic Research project entitled "Pneumonia, diarrhea and mastitis in food animals" funded by Addis Ababa University. In addition, the authors would like to thank Institute of Biotechnology, Addis Ababa University and Department of Microbiology, Immunology & Veterinary Public health, College of Veterinary Medicine & Agriculture, AAU, as well as Tigray Bureau of agriculture and rural development, MUCVM and the farming communities.