Description of an outbreak of cattle intoxication by cyanobacteria (blue-green algae) in the South of Portugal

Abstract

In 2017, 25 cows from a beef herd consisting of 54 healthy animals, with ages between 1.5 to 4 years old, from Aberdeen Angus breed x Charolais were found dead in Almodôvar, Alentejo, in the South of Portugal. They were grazing on a field of stubble for about 3 weeks when they broke the electric fence that bordered the field and had access to stagnant water from a small stream (Ribeira de Oeiras) that run across the herd. All the animals were seen healthy, by the keeper, until 12 a.m. of Sunday August 27th. When they were last observed before the occurrence, they were resting at the shade of trees and bushes surrounding the Oeiras stream. At this time of the year, this is a normal behaviour due to the high temperatures, and it is common for them to engage in grazing activities in the evening, when the temperature begins to decrease. On the next day (the 28th August), at 7 a.m., the keeper encountered 20 cadavers scattered throughout the land and 5 sick cows. The other 29 animals of the group did not show any clinical signs during the following weeks after the occurrence. In the same period, was reported the death of a heron in the Oeiras stream.