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Introduction

 Mastitis is an inflammation of the mammary glands of dairy cows accompanied by physical, chemical, pathological and bacteriological changes in milk and glandular tissue (1, 2). The disease, which is common in dairy cows, causes significant losses to the dairy industry and affects milk hygienic and sanitary features (3, 4, 5). Mastitis is also of nutritional and great technological significance in milk processing as valuable components like lactose, fat and casein are decreased while undesirable components like ions and enzymes are increased (6). The disease is usually classified as sub-clinical, acute, subacute, chronic and gangrenous based on aetio-pathological findings and observations (7).
Bovine mastitis is known to be a problem in Kenyan dairy herds from previous studies (8, 9, 10). The current prevalence of bovine mastitis has however not been estimated in Kenyan smallholder dairy cattle (with a size of 1-5 animals) in the Rift Valley region. This is despite the importance of this sector and region as evident from production statistics where over 70% of the total milk in Kenya is known to come from smallholder dairy farmers (11). The sectors animals (Bos Taurus and their crosses with Bos indicus) at various grading levels, average milk yields estimated at 1300 liters per lactation (12) from approximately 3 million dairy cattle (11).
There is therefore a need to assess the current status of inflammatory mastitis, its clinical prevalence and causal agents involved amongst this sector in Kenya. This study aimed at obtaining the information from smallholder farms within milk producing regions in the Rift Valley of Kenya to enable assessments of potential interventions in the sectors production system.

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Methods
Animals: Two hundred and fifty lactating cows were examined from 87 dairy herds in different smallholder farms in six regions (Elburgon, Njoro, Nakuru, Naivasha, Nyahururu and Naivasha) during November 2001 — June 2002. The areas from the Rift Valley represent major milk producing regions in Kenya. The breeds sampled were mainly Bos Taurus and their crosses with Bos indicus at various grading levels. Random number sampling was used in selecting the cows on the farms visited. Information on age, parity, lactation stage and previous history of mastitis was gathered. Cows were kept in semi-confinement open housing and milked twice daily. Feeding was based on forage diets largely from Napier grass fodder, Kikuyu grass, crop residues and occasional supplementation with dairy meal during milking time.

Sampling: Visual observation and palpation of the mammary gland halves and macroscopic examination of the milk was undertaken on all the cows in the study. The cases of clinical mastitis encountered were studied in detail, the following being recorded for each cow: age, clinical state (acute, subacute, chronic and gangrenous). They were then classified as follows:
Acute mastitis: Severe inflammation of the mammary gland without any marked systemic reaction.
Subacute mastitis: Inflamablemation of the mammary gland with abnormalities in milk.
Chronic mastitis: Inflammation of the mammary gland, with little change in milk where the gland was either enlarged or reduced in size.

    Gangrenous mastitis: Characterized by swollen mammary gland, cold to the touch and bluish-black in color. The affected skin area peeled off, with oozing of serous fluid. Milk was bloody and watery.
Prior to quarter sampling the teat ends were cleaned and rubbed with cotton moistened in 70 % alcohol, initial streams of milk were discarded and approximately 5 ml of foremilk collected into 10-ml polythene tubes kept on ice. A portion of each quarter milk sample was inspected for clots, discoloration or wateriness before adding the California mastitis test (CMT) reagent. The rest of the milk was immediately transported cooled (4oC) to the Microbiology Laboratory, Egerton University Njoro for bacteriological examination.

    California Mastitis Test (CMT): The CMT reagent (DeLaval, Wroclaw, Poland) and the method were used alongside the physical examinations and the test was carried out as described (13). Reactions were graded 1, 2, 3, 4, or 5 according to the Scandinavian recommendations (14).

    Bacteriological diagnosis: Isolation and identification were carried out according to the Scandinavian recommendations on examination of quarter milk samples (14,15) In brief, immediately after delivery, the milk samples were inoculated on blood agar plates (Becton Dickinson and Company, USA), which were divided into four sections. A disposable culturing loop (10µl) was dipped into the milk sample and a total of 6-8 lines made in one agar section by turning the loop once between the streaking lines. Each quarter milk sample (10µl) was thus streaked in one section of the plate as a line culture. Samples were cultivated under aerobic conditions for 24 - 72 h at 37oC and examined for bacterial growth. Pure cultures were further examined for morphological, staining and cultural characteristics, and for biochemical reactions according to standard keys (15). Staphylococci were studied in particular for haemolysis and coagulase production (tube method using oxalated rabbit plasma in a 1:10 dilution in a nutrient broth incubated at 37oC and inspected at 30 min intervals for 5-6 h for clot formation). A positive coagulase test was judged as any degree of clotting from a loose clot suspended in plasma to a solid clot (16). For the Staphylococcus aureus counts - 0.1 ml of the sample was inoculated in duplicate, at the appropriate dilutions, on Baird-Parker Agar, and incubated at 35 ± 1oC for 24-48 h before colony counting. In cases of mixed growth, a new quarter sample was taken and re-examined.

    Quarters were classified as not infected (NI) if no organisms were isolated, infected with major pathogens (MAP) if Streptococcus agalactiae, other Streptococcus species, Staphylococcus aureus, and Escherichia Coli were isolated, and infected with minor pathogens (MIP) if coagulase — negative staphylococci were isolated. Quarters were also classified as “normal” if no organisms was isolated, the udder had no injuries or indurations, the appearance of the milk was normal, and no previous history of mastitis was recorded and “abnormal” otherwise. Samples with unspecified mixed cultures were considered contaminated and thus excluded from subsequent analysis.
Statistics: The level of significance between the occurrence of each of the isolated organisms in udders with mastitis and udders without mastitis (control) was determined using the ?2 test and all values where P < 0.05 was considered as significant.


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Results

Prevalence of clinical mastitis
    A total of 250 cows (989 quarters) were examined of which 11 cows (Seven from apparently mastic and four from apparently non mastic cows) had lost a quarter each. Forty-nine cows (19.6%) displayed evidence of clinical mastitis at the cow level. The number of quarters affected was: left fore, 51; right fore, 57; left hind, 42; right hind, 39. There was no significant difference (p < 0.05) in the number of quarters affected in relation to their anatomical positions.

    The age of affected cows ranged from 2 to 10 years of which 19.6% had clinical infections from the total of cows examined (Table 1). With regard to the clinical state of the mammary gland, there was no statistical difference (P > 0.05) in age distribution with respect to the form of clinical mastitis.

Table 1. Mastitis cows (n=250) from the Rift Valley Highlands, Kenya, grouped according to the clinical state of the mammary gland in various age groups.

The average milk production per quarter was 1.83+/-0.12. The results for the CMT scores are shown in table 2.

Table 2. CMT scores of milk samples from 989 quarters in the  dairy herds.

The frequency of bacterial species cultured from each of the quarter milk samples from the 201 non-mastitic and 49 mastitic udders is shown in Table 3.

Table 3. Frequency of various types of bacteria isolated from apparently affected (n=191) and apparently unaffected milk of cows (n=798).
 

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Discussion

    The present study was carried out on selected herds located in the Rift Valley of Kenya to determine the true infection status of cow/quarters by microbiological analysis (culturing) of aseptically taken milk samples. This area has numerous smallholdings (farms) and a small number of larger herds. The standard of milking hygiene was poor on the majority of the farms sampled. Preventive measures, such as the use of udder disinfectants, post-milking teat dipping and dry cow therapy, were observed to be infrequent in these herds. In the majority of the herds (74%) there was no surveillance program in place for mastitis.

    Staphylococcus aureus and CNS were the major mastitis-inducing pathogens detected in this study (Table 3). This finding was similar to reports from earlier investigations in other regions in Kenya (9, 10, 17) and Tanzania (18) indicative of the commonness of S. aurues mastitis in the small dairy sector. The results may be suggestive of a possible development of resistance from prolonged and indiscriminate usage of beta — lactam antibiotics as evident from a previous study (19).

    Because the quality of the milk cannot be improved following extraction from the cow, production of high quality milk requires an efficient mastitis control program. Cows with a high prevalence of mastitis as in this study are incapable of producing high quality milk until the inflammation and infection in the udder are brought under control. This has severe economic implications for the milk producer, as the milk is no longer marketable and other animals are easily infected. Treatment and decrease in milk volume also cause considerable losses per animal.
Systematic records regarding the epidemiology of cow mastitis, status of infection, treatment patterns would provide useful management information to the producer, veterinarian and other mastitis control team members. This has been evident from countries where records have been documented regularly internationally such as in Norway (20) since 1975, 1982 in Finland (21) and 1984 in Sweden (22). There is thus a need to routinely investigate and record the epidemiology of bovine mastitis and antibiogram sensitivity of bacterial isolates from the smallholder sector in Kenya.

Acknowledgements
    We are gratefully to the Swedish Institute (SI) for financial assistance. We thank Emil Olden and Claes Ericksson (SLU-Uppsala) for their input in the laboratory analysis and are grateful to dairy owners and herders in the Rift Valley province for their cooperation. Special thanks are extended to Professor Åse Sternesjö (SLU) and Dr.Carlos Concha of the Swedish Veterinary Associaition - Uppsala for technical advice and guidance. We thank Mrs Lotta wall for her coordination of supplies from Sweden to Kenya and Professor Mahungu Symon for permission to use the microbiology laboratory at the Guildford Institute — Egerton University Kenya.
 

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LINKS TO OTHER ARTICLES IN THIS ISSUE

References

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