Although seasonality is recognised as an important part of agricultural-based livelihoods, limited literature is available on the subject area, and it is often only alluded to in discussion of other aspects of rural livelihoods. A 2-year longitudinal study to examine the influences of seasonal changes on livestock keeping in a smallholder crop-livestock production system was carried out in Busia District, western Kenya. The study aimed to obtain a picture of yearly variations in household activities and resources, as a means of understanding decisions made by households regarding animal health management, and household times of vulnerability in terms of losing animals. Data collection coincided with the three main seasons in the study area. Information on (inter alia) seasonal livelihood activities, animal health care expenses, numbers of disease episodes and livestock movements into and out of households was collected using questionnaires and participatory rural appraisal methodologies. Farmers suggested clear and consistent seasonal changes and events, but data analyses did not show the patterns expected in relation to livestock keeping. Important observations were made in relation to livestock disease episodes and the use of veterinary services; livestock disease episodes were higher during the long rains than in the dry season, but more money was spent during the dry season when numbers of disease episodes were low, and more households also used professional veterinary services during this season (chi (2) = 81.47, P < 0.001). In both study years, a higher proportion of households treated animals themselves during the rainy seasons (z = -2.4, P = 0.02; z = -5.03, P < 0.001).