Clinical and subclinical mastitis in smallholder dairy farms in Tanzania: Risk, intervention and knowledge transfer

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Abstract

In a cross-sectional study of 400 randomly selected smallholder dairy farms in the Tanga and Iringa regions of Tanzania, 14.2% (95% confidence interval (CI) = 11.6–17.3) of cows had developed clinical mastitis during the previous year. The point prevalence of subclinical mastitis, defined as a quarter positive by the California Mastitis Test (CMT) or by bacteriological culture, was 46.2% (95% CI = 43.6–48.8) and 24.3% (95% CI = 22.2–26.6), respectively. In a longitudinal disease study in Iringa, the incidence of clinical mastitis was 31.7 cases per 100 cow-years. A randomised intervention trial indicated that intramammary antibiotics significantly reduced the proportion of bacteriologically positive quarters in the short-term (14 days post-infusion) but teat dipping had no detectable effect on bacteriological infection and CMT positive quarters. Other risk and protective factors were identified from both the cross-sectional and longitudinal included animals with Boran breeding (odds ratio (OR) = 3.40, 95% CI = 1.00–11.57, P < 0.05 for clinical mastitis, and OR = 3.51, 95% CI = 1.29–9.55, P < 0.01 for a CMT positive quarter), while the practice of residual calf suckling was protective for a bacteriologically positive quarter (OR = 0.63, 95% CI = 0.48–0.81, P  0.001) and for a CMT positive quarter (OR = 0.69, 95% CI = 0.63–0.75, P < 0.001). A mastitis training course for farmers and extension officers was held, and the knowledge gained and use of different methods of dissemination were assessed over time. In a subsequent randomised controlled trial, there were strong associations between knowledge gained and both the individual question asked and the combination of dissemination methods (village meeting, video and handout) used. This study demonstrated that both clinical and subclinical mastitis is common in smallholder dairying in Tanzania, and that some of the risk and protective factors for mastitis can be addressed by practical management of dairy cows following effective knowledge transfer.

Introduction

Mastitis in dairy cows occurs worldwide and can be caused by infections with bacteria, yeast and fungi (Bramley and Dodd, 1984, Costa et al., 1997, Moretti et al., 1998, Bradley and Green, 2001). Bacteria are the most common cause of intramammary infection and the range of causal bacterial species varies with geographical location and management. In previous studies in developing countries, yeast or fungi represent a greater proportion of isolates than those from developed countries, possibly indicating different exposure levels, host susceptibility, or increased contamination of collected milk samples (Moretti et al., 1998, Krukowski et al., 2001). Losses associated with mastitis include reduced milk production and lowered milk quality (Mattila et al., 1984, Fang et al., 1993).

Mastitis occurs in both clinical or subclinical forms. Although subclinical mastitis is more prevalent than clinical mastitis in developing countries, as subclinical disease is not manifested as visible changes in the mammary glands or in the milk, it is therefore not easily recognised by farmers (Shekimweri, 1992, Omore et al., 1996). Although mastitis is well recognised as one of the major diseases of economic importance in the dairy industry in different countries (Hamir et al., 1977, Kossaibati et al., 1998), few studies have been conducted on this disease in Tanzania where it may cause both economic effects and result in a poorer source of nutrition. Information on the aetiology, prevalence and incidence of clinical mastitis in Tanzania is limited, especially in the smallholder dairy sector. In most studies of mastitis in Africa and in other developing countries, contagious pathogens have been shown to predominate over environmental pathogens (Kinabo and Assey, 1993, Omore et al., 1996). In large-scale dairy farms in Tanzania, the annual clinical incidence of mastitis was reported to range from 1.5 to 3.2 cases per 100 cows (Kinabo and Assey, 1993, Kambarage et al., 1996), while the prevalence of subclinical mastitis, based on isolation of pathogens from clinically normal quarter milk samples in Ethiopia, was reported to be 39% (Abdella, 1996), and 33–39% in Kenya and Ethiopia by the California Mastitis Test (CMT) (Kassa et al., 1999, Mulei, 1999). Large epidemiological studies to identify risk and protective factors for mastitis in smallholder dairy cattle have not been carried out in Tanzania. This information is required to inform current and future management practices for mastitis and to optimise milk production in this sector.

Smallholder dairy farming is a relatively recent undertaking in Tanzania which became established in the 1980s in order to contribute to the milk supply after large government-owned farms failed to meet consumer demand (Ministry of Agriculture and Cooperatives, MOAC, 1997, Sumberg, 1997). The principal sources of dairy animals for this livestock sector include dairy development programmes (DDPs), especially in rural areas, or purchase from neighbours and large-scale farms in urban areas. The majority of cattle on smallholder dairy farms are crossbred animals, usually crossbred from traditional Bos indicus and exotic Bos taurus breeds, which typically are low-yielding animals producing an average of 5–6 l/day (Karimuribo, 2002). The smallholder dairy sector contributes significantly to poverty alleviation and reduction of malnutrition particularly in rural and peri-urban areas in addition to providing regular income to the household and employment opportunities for women and animal attendants.

Advice to farmers about livestock and crop systems in developing countries is mostly available through extension services, which are often funded by government or non-governmental organisations. However, in Tanzania there is lack of knowledge about the most appropriate methods of delivery of such services (MOAC et al., 1998). The importance of verbal and visual representations to learning has been previously investigated and it is thought that humans have separate verbal and visual processing systems (Clarke and Paivio, 1991, cited by Mayer, 1999) and that connection with existing knowledge is important in enabling understanding of new experiences (Alber and Hasher, 1983, cited by Nuthall, 1999).

In this study we aimed to quantify the prevalence and incidence of cause-specific mastitis in smallholder dairy cows, evaluate mastitis control and knowledge dissemination methods, and then transfer knowledge about mastitis to smallholder dairy farmers in Tanzania.

Section snippets

Study area

As component of a research project funded by the Department for International Development (DFID, UK), a study on mastitis was carried out in two regions of Iringa and Tanga in Tanzania. The two regions have different geographical locations and climatic conditions. Iringa is situated between latitudes 7° and 8° South and longitudes 35° and 36° East in the Southern Highlands and Tanga region is located between latitudes 4° and 6° South and longitudes 36° and 38° East along the coast of the Indian

Rapid rural appraisal

The rapid rural appraisal indicated that illiteracy was identified as a problem especially amongst cowboys and women in rural areas. Disease knowledge was generally poor with the exception of the tick-borne diseases, especially East Coast Fever. Although some farmers stated that they had seen mastitis in either their own, or in neighbours, dairy cows, their awareness of clinical mastitis and its treatment and control in general was poor and they were unaware of subclinical mastitis. The

Discussion

Mastitis, in both its clinical and subclinical forms was found to be common in Tanzania and contagious pathogens were found to be more common than environmental pathogens, with S. aureus being isolated most frequently. The prevalence of subclinical mastitis in the current study, defined by CMT positive cows and quarters, was high (76% and 46%, respectively). Other recent studies reported a slightly lower prevalence of 62% of cows positive by CMT in Tanzania (Malole, 1998), and 33% of quarters

Acknowledgements

The project was funded by the Department for International Development. The help and support of the Southern Highlands Dairy Development and the Tanga Dairy Development Programmes are gratefully acknowledged.

The project would not have been possible without the help and co-operation of the farmers, village leaders, and extension officers in Iringa and Tanga regions of Tanzania.

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