Brucellosis infection dynamics in cattle and the impacts on production and reproduction in pastoral settings of Tanzania

Brucellosis is endemic in pastoral settings of Tanzania with significant socio-economic implications. However, comprehensive studies to establish its impacts had not been elucidated. A longitudinal study was conducted in order to elucidate the dynamics and its impact on production and reproduction. Initially, 464 animals were enrolled with baseline seroprevalence in each herd. Animals were bled every three months to determine the incidence rate, impacts and trends in sero-status. In addition, individual animal reproductive information was collected. Milk yield was measured indirectly by estimating the calves’ growth rate. Data were analysed using Epi Info 7.0 software where descriptive analyses were used to establish proportions, associations and relationships. Wilcoxon test was used to establish the growth rate differences. Forty-seven new c-ELISA seropositive animals were identified over the period of three months representing an incidence rate of 0.811 cases per animal-year at risk. Households with a high seroprevalence during baseline screening were observed to have high infection rate in the subsequent visit. There was no statistical association between new seropositive cases and seasons (P>0.05). Furthermore, positive to negative seroconversion was observed. Of the 94 females that were expected to parturate, 15% aborted with 29% of these being seropositive. Retained placenta was observed in 4.3% of the domestic ruminants. Of the 79 calves that were screened, 21.5% were seropositive with majority born from seropositive dams. Calves born from seropositive dams were 27 times more likely to be seropositive. Growth rate was not different (p>0.05) between calves suckling from seropositive and seronegative dams.