Sewerage overflows put production and fertility of dairy cows at risk

More than 50% of the dairy farmers in the Netherlands use surface water as the main source of drinking water for their cows during the grazing season. The quality of this water mag be affected by discharges from sewerage over flows, but possible effects on health of dairy cows have not been quantifie d. Our objective, therefore, was to assess the risk of impaired production and fertility in dairy cows that drink surface mater in direct contact with a sewerage overflow, Standardized milk production: of-cows from 60 farms u sing surface water in direct contact with a sewerage overflow was 0.9 L d(- 1) less (P = 0.09) than that of cows from 397 farms using surface water not in contact with an overflow. Also, age at first calving was 20 d higher (P < 0.01) in heifers exposed to drinking water in contact with sewerage over flows. These results strengthen earlier suggestions that sewerage overflows mag reduce production and fertility of dairy cows.