Ingestion of toxic Microcystis aeruginosa by dairy cattle and the implications for microcystin contamination of milk

Microcystin (MCYST) toxins can be produced by the bloom-forming cyanobacter ium Microcystis aeruginosa. They are chemically stable compounds and have b oth acute and chronic effects on the health of mammals, including cattle an d humans. Cattle will drink water containing lethal cell concentrations of M. aeruginosa. When cattle consume sub-lethal doses of microcystins, the fa te of those toxins is unknown. We provided drinking water containing 1 x 10 (5) cells ml(-1) M. aeruginosa (strain MASH01-A19) to four lactating Holste in-Friesian dairy cattle for 21 days to determine if MCYST-LR produced by t he cyanobacteria, could be detected in milk produced by the cattle. Cattle consumed up to 15 mg MCYST-LR at an ingestion rate of 1.21 mug kg (live wei ght) d(-1). Analysis by HPLC and ELISA indicated that no detectable amounts of microcystin from the cyanobacteria were present in the milk obtained fr om the treated animals. Based on the level of quantitation of the ELISA ana lyses, the maximum possible concentration in the milk was less than 2 ng l( -1). This is more than three orders of magnitude less that the concentratio n that could be considered problematic for milk of 0.86 mug l(-1) which we calculated using the World Health Organization derived tolerable daily inta ke for MCYST-LR and the per capita daily consumption of milk in Australia. (C) 2001 Elsevier Science Ltd. All rights reserved.