Sewerage overflows put production and fertility of dairy cows at risk

More than 50% of the diary 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 may be affected by discharges from sewerage overflows, but possible effects on health of dairy cows have not been quantified. Our objective, therefore, was to assess the risk of impaired production and fertility in dairy cows that drink surface water in direct contact with a sewerage overflow. Standardized milk production of cows from 60 farms using 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 overflows. These results strengthen earlier suggestions that sewerage overflows may reduce production and fertility of dairy cows.