Abstract Poor milk safety constitutes a persistent public health risk in Kenya. Poor milk composition, microbial contamination and adulteration is a constraint to dairy sector development. We hypothesise that variation in milk quality and safety depends on variation between farming systems. We argue that this variation between farming systems is associated with spatial location which affects the agro-ecological conditions and the availability of labour and land. We used a spatial framework based on the distance to urban markets to distinguish the following farming systems: relatively intensive dairy systems in urban locations (UL), semi-intensive dairy systems in mid-rural locations (MRL) and extensive dairy systems in extreme rural locations (ERL). We aimed to investigate the variation in the quality of raw milk in these dairy farming systems and associated value chains in central Kenya. For this reason, we combined several methods such as participatory rural appraisal, participant observation, and milk physicochemical and microbiological analyses to collect data. Milk samples were collected at the informal and informal value chain nodes - farms, informal collection centres, informal retailing centres including milk vending machines, and formal bulking centres - where milk changes hands between value chain actors. Milk quality was compared to standards recommended by the Kenya Bureau of Standards (KeBS). There were no differences in the quality of raw milk between locations or between nodes. The overall milk physicochemical composition means (standard error) of the milk were within KeBS standards: fat 3.61 (0.05), protein 3.46 (0.06), solid-not fats 9.18 (0.04), density 1.031 (0.0002) and freezing point −0.597 (0.019). The protein percentage was below KeBS standards at all value chain nodes, except at the formal bulking node. There was significant contamination of milk samples: 16.7% of samples had added water, 8.8% had somatic cell count SCC above 300,000, 42.4% had E. coli, 47.9% had Pseudomonas spp., 3.3% had Staphylococcus spp. and 2.9% tested positive for brucellosis antibodies. Unsanitary milk handling practices were observed at farms and all value chains nodes. Milk physicochemical composition except for protein content meets the KeBS Standard. High levels of microbial contamination of milk pose a public health risk to consumers and show that urgent action is needed to improve milk quality.

中文翻译：

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肯尼亚奶牛养殖系统和相关价值链的牛奶质量：成分、污染和掺假分析

摘要 牛奶安全性差是肯尼亚持续存在的公共卫生风险。牛奶成分差、微生物污染和掺假是乳制品行业发展的制约因素。我们假设牛奶质量和安全性的差异取决于养殖系统之间的差异。我们认为，农业系统之间的这种差异与影响农业生态条件以及劳动力和土地可用性的空间位置有关。我们使用基于到城市市场距离的空间框架来区分以下农业系统：城市地区的相对集约化奶牛系统 (UL)、中农村地区的半集约化奶牛系统 (MRL) 和极端农村地区的粗放奶牛系统。位置 (ERL)。我们旨在调查肯尼亚中部这些奶牛养殖系统和相关价值链中原料奶质量的变化。为此，我们结合参与式农村评价、参与观察、牛奶理化和微生物分析等多种方法收集数据。牛奶样本是在非正式和非正式价值链​​节点——农场、非正式收集中心、包括牛奶自动售货机在内的非正式零售中心和正式的散装中心——收集的——牛奶在价值链参与者之间易手。牛奶质量与肯尼亚标准局 (KeBS) 推荐的标准进行了比较。不同地点或节点之间的原料奶质量没有差异。牛奶的整体物理化学成分平均值（标准误差）在 KeBS 标准范围内：脂肪 3.61 (0.05)、蛋白质 3.46 (0.06)、固体非脂肪 9.18 (0.04)、密度 1.031 (0.0002) 和冰点 -0.597 ( 0.019）。除正式膨胀节点外，所有价值链节点的蛋白质百分比均低于 KeBS 标准。牛奶样品污染严重：16.7% 的样品加水，8.8% 的体细胞计数 SCC 超过 300,000，42.4% 有大肠杆菌，47.9% 有假单胞菌属，3.3% 有葡萄球菌属。2.9% 的人布鲁氏菌病抗体检测呈阳性。在农场和所有价值链节点都观察到不卫生的牛奶处理做法。牛奶理化成分除蛋白质含量外均符合KeBS标准。