Mastitis in smallholder dairy and pastoral cattle herds in the urban and peri-urban areas of the Dodoma municipality in Central Tanzania

R H Mdegela, E Karimuribo, L J M Kusiluka, B Kabula, A Manjurano, A M Kapaga^* and D M Kambarage

Sokoine University of Agriculture, Department of Veterinary Medicine and Public Health, P. O. Box 3021, Morogoro, Tanzania
rmdegela@yahoo.com   /   mdegela@suanet.ac.tz
*Animal Disease Research Institute, Ministry of Water and Livestock Development, P. O. Box 9254, Dar es Salaam, Tanzania

Abstract

A cross-sectional study involving 64 smallholder dairy cattle was carried out in urban and peri-urban areas of Dodoma municipality situated in the semiarid central part of Tanzania in order to determine milking practices and prevalence of mastitis, bovine tuberculosis and brucellosis. Nineteen pastoral herds were also included in the study. A questionnaire survey was used to assess milking practices while clinical examination of animals, California mastitis test (CMT) and microbiological assessments of milk were used to establish the status of mastitis. Enzyme-linked immunosorbent assay (ELISA) and single comparative intra-dermal tuberculin tests (SCITT) were used to determine the prevalence of bovine brucellosis and tuberculosis respectively. In addition, milk samples were cultured for isolation of Mycobacterium species using standard techniques.

While all animals were free of clinical mastitis at the time of farm visits, based on CMT at animal level, the prevalence of sub-clinical mastitis was significantly higher in dairy (61.2%) than in the traditional cattle (26.3%). Based on cultures, the prevalence of mastitis was also significantly higher in dairy animals at both herd and animal levels than in traditional animals. The isolation rates of aerobic bacteria, anaerobic bacteria, yeast, mucor and aspergillus in dairy herds at animal level were 62.4%, 0%, 30.6%, 1.2% and 8.2% respectively, whereas in the traditional animals, the isolates were aerobic bacteria (39.5%) and aspergillus (13.2%). In both dairy and traditional cattle, aerobic bacterial isolates comprised Staphylococcus epidermidis (55), Staphylococcus aureus (14), Staphylococcus intermedius (1), unidentified Staphylococcus species (26), Escherichia coli(7), Klebsiella spp (6), Serratia spp (6), Arcanobacter pyogenes (2), Bacillus spp (2) and unclassified bacteria (3). Whereas the seroprevalence of brucellosis was 3.9% and 4.8% in dairy and traditional cattle respectively, all tested animals were negative based on SCITT. Atypical mycobacteria were isolated from milk in dairy (15.3%) and traditional (5.1%) animals and the isolates comprised Mycobacterium gordonae (4), Mycobacterium phlei (3), Mycobacterium fortuitum (3); Mycobacterium smegmatis (2), Mycobacterium flavescens (2) and Mycobacterium avium intracellulare complex (1).

The findings indicate that the prevalence of mastitis might be lower in the traditional sector than in smallholder dairy animals and that consumption of raw milk may be associated with health risks to consumers in relation to brucellosis and atypical mycobacteria infections albeit their low prevalence.

Key words: Cattle, dairy, mastitis, pastoral, smallholder, Tanzania

Introduction

The optimal milk productivity of dairy animals in Tanzania has not yet been realized due to several constraints that include poor animal management, poor feeding particularly during the dry season when pastures become scarce, and the high prevalence of diseases as a result of poor disease control. The major health constraints in Tanzania include tick-borne diseases, trypanosomoses, helminthosis and nutritional disorders. On the other hand, mastitis is also increasingly being incriminated as an important disease in dairy animals (Schepers and Dijkhuizen 1991; Shekimweri 1992; Nangwala and Kurwijila 1995; Kambarage et al 1996; Mdegela et al 2004). The sub-clinical mastitis, which is the most prevalent in Tanzania (Shekimweri 1992; Omore et al 1996; Karimuribo 2002; Shem et al 2002; Mdegela et al 2004) and elsewhere can cause reduction in milk yields of about 70% (Sandholm et al 1990).

Although mastitis has been recorded as one of the major diseases of economic importance in the dairy industry worldwide (Radostitis et al 1999), few studies have been conducted on this disease in Tanzania, particularly in the smallholder dairy sector (Shekimweri 1992; Karimuribo 2002; Shem et al 2002; Mdegela et al 2004). In addition, previous studies carried out in Tanzania were centred on conventional bacteriological assessments. Udder infections involving non-conventional pathogens such as anaerobic bacteria, mucor, yeast, aspergillus and mycoplasmas, which may also partly be influenced by milking practices and general hygiene have been documented in only one study in the smallholder dairy sector (Mdegela et al 2004). The status of milk-borne zoonoses such as brucellosis and tuberculosis, with special reference to Mycobacteria bovis and mycobacteria other than tuberculosis (MOTTs) are also of special interest because of the public health risks that are associated with consumption of raw and naturally fermented milk. Furthermore, although, infections attributable to M. bovis occur in foci in Tanzania (Kazwala 1996), it appears that infections with MOTTs are common in milk (Ngotonie 1999; Shirima 1999; Mdegela et al 2004). Udder infections and the public health risks related to MOTTs, M. bovis and brucellosis could only be minimized if adequate data on health risks are gathered and risk assessments carried out in order to help to devise effective udder infections mitigation strategies. As an attempt towards achieving this, the current study aimed at assessing the status of mastitis, milking practices and the prevalence of bovine brucellosis and tuberculosis in smallholder dairy animals. A preliminary survey was also carried out in traditional animals kept under the smallholder animal set up in and around the Dodoma municipality in order to shed some light on the level of mastitis, bovine tuberculosis and brucellosis.

Materials and methods

Study area

This study was conducted in July-October 2002 in nine wards in the urban and periurban areas of Dodoma municipality that has a semi-arid climate, which is characterised by a long dry season lasting between late April and early December, and a short wet season occurring during late December and early April. The average annual rainfall is about 570 mm and temperature ranges between 18^oC and 31^oC.

Sampling procedure and determination of the prevalence of mastitis, brucellosis and tuberculosis

A total of 64 smallholder dairy farms with average herd size of 5.53±0.61 (mean ± SD), and 19 traditional herds with average herd size of 12.7±2.59 were randomly selected from a sampling frame of herds in nine wards of Dodoma municipality. A pre-tested and standardised questionnaire was administered to all selected households to assess the knowledge on mastitis and milk-borne zoonoses and to identify practices related to milking hygiene.

In all 83 selected herds, all milking animals were clinically examined for evidence of pain, swelling and, changes in colour and consistency of the udder and milk. Evidence for sub-clinical mastitis for each quarter was checked using CMT. About 3.0 ml of milk samples from each of the functional quarter were collected aseptically into sterile universal bottles for aerobic and anaerobic bacteriological assessments including that of mycobacteriosis and mycotic infections. Collected samples were stored in cool boxes and transported immediately to the laboratory. Blood samples were collected into plain vacutainer tubes from animals above one year of age in the selected herds. Serum was extracted from collected blood for serological screening for brucellosis. The animals were also tested for tuberculosis using avian and bovine purified protein derivatives (PPDs), kindly supplied by the Central Veterinary Laboratory, Addlestone, Surrey, England. Briefly, avian and bovine tuberculins (each 0.1 ml containing 2500 IU) were administered intra-dermally in the cervical region at a distance of 12.5 cm apart. Prior to inoculation, the skin fold thickness at each site was measured using a pair of callipers (Barr-Knight Engineers Glasgow, UK). After 72 hours, the skin fold thickness at each site was measured again and the interpretation of results was carried out using standard procedures (Kazwala 1996).

One aliquot of the collected milk was cultured for anaerobic and aerobic bacteria (Carter et al 1991) and identified by Gram-stain and biochemical tests (Carter et al 1991; Roger and Edmundson 2000). Susceptibility of aerobic isolates to antimicrobial agents was carried out using amoxycilin, neomycin, oxytetracycline, penicillin G, chloramphenicol, streptomycin and cephalexin sensitivity discs (NCCLS 1994) by culturing the isolates on Mueller-Hinton agar at 37^oC for 24 hours and measuring the inhibition zone. The inhibition zone equal or greater than 13 mm was considered as positive and for less than 13 mm, the isolates were considered to be resistant to the drug.

Another aliquot of each milk sample was cultured for mycotic agents using the Saboraud Dextrose Agar (SDA) and incubated at room temperature (22^oC) and at 37^oC and examined daily for up four weeks. Fungal growth was characterized by morphology and identified using standard procedures (Quinn et al 1998). The third aliquot of milk was used for mycobacteriologiocal assessment. Briefly, for recovery of Mycobacterium bovis and MOTTs, the milk was decontaminated with an equal volume of 4% sodium hydroxide (PARK Scientific Ltd, Northampton, UK), neutralized with 14% potassium dihydrogen ortho-phosphate (BDH Laboratories Supplies, England) buffer containing 0.1% phenol red indicator (Fison Scientific Equipment, Loughborough UK) and centrifuged at 3,000x g for 20 minutes. The supernatant was then decanted into containers containing cresol soap and then sterilized at 121^oC for 30 minutes. Sediments were thereafter inoculated onto Lowensten-Jensen (LJ) medium with pyruvate and on LJ medium with glycerol (Collins et al 1985; Groothuis and Yates 1991), incubated at 37^oC for 12 weeks. Observation for growth was done on days three and seven and, then on weekly basis. Positive cultures were confirmed using Ziehl-Neelsen staining and thereafter sub-cultured on LJ and parabenzoic acid (PBA) media at 37^oC for 2-3 weeks. Isolates in LJ medium were then subjected to niacin, oxygen preference, tween hydrolysis, pigmentation and temperature tests (Collins et al 1985; Groothuis and Yates 1991).

Collected data were entered in Epi Info 6 database (Coulombier et al 2001) and the association between mastitis and risk factors was determined using 2X2 contingency table in Epi Info 6 Statcalc programme. Strength of the association between a risk factor and mastitis was examined by relative risk (RR). Statistical difference between proportions was determined using Epi Info 6 Epitable programme, with a critical probability of P=0.05. The Epitable programme was also used to calculate 95% confidence interval (CI) of the proportions and exact binomial 95% CI values were used.

Results

Type of animal houses and milking practices

Seventy three percent of the herds were housed in cowsheds with roofs and the rest were kept in unroofed cowsheds. The majority (90%) of the animals kept in kraals were traditional cattle. It was also evident that 39% of the floors were of the earth type, 23% were hardcore and 21% of concrete type. Extra bedding in form of either dried grass or forage was provided in 13.3% of the animal houses visited during the study.

In all farms, milkers washed hands every time before milking (Figure 1) however 46% used water alone, 52% washed with soap and 2% with disinfectants.

Although 86.7% of farms reported to wash the udder before milking 80.6% used warm and 19.4% cold water. In about 60% of the farms, calves were introduced to stimulate milk let down and 72% applied a variety of lubricants including commercial milking salve (60%), cooking oil (30%), petroleum jelly (8.3%) and fresh milk or locally prepared milk salve (3.3%) (Figure 2).

In addition, it was evident that out of 62 smallholder dairy farms, only 33.9% practiced foremilk examination at every milking and this was also the case for 15.8% out of the 19 traditional herds. None of the farmers used cloth to dry teats. Only one smallholder dairy farmer used post-milking teat dipping as a mastitis control strategy. Stripping was the most common method of milking with the squeezing method being in 5% of the farms. It was also observed that most of the farms (80%) practiced residual calf suckling after every milking and that none of the farmers used dry cow therapy as a method for controlling udder infections.

Awareness of farmers on mastitis

Based on farmers recall ability, 38% and 50% of the smallholder dairy farmers and traditional livestock keepers respectively, reported to have seen clinical mastitis in their cows. Between January 2001 and May 2002, about 25% of farms reported to have had clinical mastitis cases (Table 1). Most traditional livestock keepers associated clinical mastitis with tick infestation. Despite their awareness on clinical mastitis, none of the farmers in both the smallholder dairy and traditional farming sectors were aware of the sub-clinical form of the disease.

Prevalence of sub-clinical mastitis

Overall, the cow-based prevalence of sub-clinical mastitis defined by a cow having at least one CMT positive quarter was 50% (Figure 3).

Stratification of this prevalence by type of cow showed a significantly higher prevalence in dairy (61.2%) than in traditional cattle (26.3%) (P < 0.001). Various microorganisms were isolated from aseptically collected milk samples from each quarter (Table 2).

A significantly higher proportion of smallholder dairy herds had aerobic bacterial isolates than the traditional ones (P < 0.001). Aerobic bacterial isolates that were recovered from milk included Staphylococcus epidermidis (55), Staphylococcus aureus (14), Staphylococcus intermedius (1), unidentified Staphylococcus species (26), Escherichia coli (7), Klebsiella spp (6), Serratia spp (6), Arcanobacter pyogenes (2), Bacillus spp (2) and unclassified bacteria (3). Thirty six percent of dairy farms were positive for yeast and none of the traditional herds had yeast isolates. Whereas 2% of smallholder dairy herds were positive for Mucor species, none were isolated from traditional farms. The isolation rate of Aspergillus species was significantly higher (p<0.001) in traditional herds than in smallholder dairy herds.

Drug susceptibility profiles of aerobic bacterial isolates

Bacterial isolates including Arcanobacter species, Bacillus species, Escherichia coli, Klebsiella species, Serratia species, Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus intermedius, Staphylococcus species and unclassified organisms were subjected to various drug susceptibility tests. Of the tested isolates 94.3% were susceptible to Amoxycillin; 92.6% to neomycin; 91% to cephalexin; 86.9% to streptomycin; 75.4% to oxytetracycline; 73.0% to chloramphenicol and 69.7% to penicillin. Resistance to penicillin, streptomycin and oxytetracycline involved Serratia species, Staphylococcus epidermidis and unidentified Staphylococcus species.

Milk-borne zoonoses

Based on ELISA, 4.2% of the animals seroconverted to brucellosis and these comprised 3.9% dairy animals (n=154) and 4.8% (n=62) traditional cattle. Although, all animals reacted negatively to SCITT, out of the 123 pooled milk samples, 12.2% were positive for atypical Mycobacterium species (MOTTs) and this involved 13 dairy animals (n=85) and two (n=39) traditional cattle. The species of MOTTs that were isolated included Mycobacterium gordonae (4); Mycobacterium phlei (3); Mycobacterium fortuitum (3); Mycobacterium smegmatis (2); Mycobacterium flavescens (2) and Mycobacterium avium intracellulare complex (1).

Discussion

The findings of this study highlight the high prevalence of sub-clinical mastitis (Shem et al 2002) thus indicating the potential economic implications related to the disease in smallholder dairy sector (Shekimweri 1992; Omore et al 1996, Karimuribo 2002 and Mdegela et al 2004) as it can cause immense losses in milk production (Janzen 1970 and Sandholm et al 1990). Such a high prevalence of the disease in smallholder dairy sector as also observed in large-scale farms (Kinabo and Assey 1983) is partly attributable to poorhouse hygiene and lack of disease control practices. The fact that the majority of the animal houses had earth type of floors which is difficult to clean especially during the rainy period; that hygienic milking practices were poor and, that none of the farmers used the dry cow therapy and were aware of the existence of the sub-clinical form of mastitis highlight the potential implication of mastitis in Tanzania. Since, worldwide, sub-clinical mastitis is regarded to be the major cause of milk losses attributable to udder infections and given the value of the few animals have on the livelihood of the smallholder dairy farmers in Tanzania, it is important that measures are taken to educate farmers on the importance of improving animal husbandry practices and adopting better milking hygiene measures along with the use of CMT in disease monitoring.

A comparison between dairy and traditional animals showed that the prevalence of sub-clinical mastitis was significantly lower in traditional cattle than in dairy animals and this is despite the poor hygiene in kraals in the traditional herds that would have been expected to lead to high udder infection rates. These results appear to agree with the preliminary observation made by others in Tanzania (Shem et al 2002). It is possible that low prevalence of sub-clinical mastitis in traditional animals is attributable to genetic resistance (Payne and Wilson 1999), the inherent low milk productivity and the observed prolonged period for which calves are allowed to suckle their dams in the traditional herds. The latter is linked to the fact that calf sucking is a protective factor for mastitis (Karimuribo 2002; Mdegela et al 2004). However, more studies are needed to shed more light on this differential udder infection rates between traditional and dairy animals.

The preponderance of Staphylococcus species in the study animals has also been observed in other studies in Tanzania (Mahlau and Hyera 1984; Karimuribo 2002; Mdegela et al 2004) and the associated antimicrobial susceptibility profiles of the isolates were similar to those reported in a similar study that was carried out in the smallholder dairy animals in the eastern part of Tanzania (Mdegela et al 2004). The other important significant finding was the recording of fungal microorganisms in milk. The prevalence of fungal isolates, especially yeasts and mucor in the dairy animals was observed to be higher than in traditional cattle and this may partly be attributed to the use of antimicrobials that is more common in smallholder dairy sector than traditional animals. However, this observation also requires further investigation. On the other hand, it is not yet clear as to the factors that can explain the high recovery rates of Aspergillus species in traditional cattle than in dairy ones.

The status of brucellosis in smallholder dairy and traditional animals was low as also observed by Weinhaupl et al (2000) in traditional cattle herds and by Mdegela et al (2004) in smallholder dairy animals in coastal part of Tanzania. This is despite the lack of disease control programme such as the use of S₁₉ vaccine. The low prevalence of brucellosis in smallholder dairy animals could be due to minimal pasture contamination as a result of confinement of animals under the cut and carry feeding system and low stocking rates in communal grazing areas for the few herds where animals are taken out for grazing. However, since some of the animals are positive, it is still important to caution farmers and consumers on the public health risks that are associated with mixing milk from infected and non infected animals. It is possible that through health education, farmers with infected animals may agree to cull the infected ones.

The isolation of MOTTs from milk as also previously observed (Shirima 1999 and Mdegela et al 2004) in the smallholder dairy animals is of great public health concern in that although, most species are not pathogenic to humans, they can assume a pathogenic role in immuno-compromised subjects and in situations related to drug abuse and alcoholism. With the risks posed by the HIV/AIDS pandemic in Tanzania and the continued preference for raw and naturally fermented milk especially in rural areas and with some of the town dwellers, the public health risks due to atypical Mycobacterium species can no longer be ignored. This therefore, calls for formulation of health education aimed at changing milk consumption habits with emphasis being on boiling the milk before consumption.

Conclusions

• The prevalence of mastitis was lower in the traditional sector than in smallholder dairy animals

• Consumption of raw milk may be associated with health risks to consumers in relation to brucellosis and atypical mycobacteria infections albeit their low prevalence.

Acknowledgements

This work was financially supported by AICAD to which authors are most grateful. The technical assistance offered by laboratory technicians at SUA Morogoro and Animal Disease Research Institute in Dar es Salaam during sample analysis is highly appreciated. Cooperation from veterinarians, extension officers and farmers in the study area is highly acknowledged.

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