The number of cases of BSE found in the national herd during September was 15, making it one of the worst months since the disease was first identified here in 1989.
Yesterday's figures bring to 90 the number of cases detected so far this year - 44 more than in the same period last year.
However, in only two other months since 1989 have there been more than 15 cases of the disease, which leads to collapse of the central nervous system in infected cattle.
According to the Department of Agriculture, the 15 cases include two cases of BSE found in follow-up investigations of herds where cases had already been identified.
The most positive aspect of yesterday's figures, according to the Department of Agriculture, was that all the animals were aged five years or more, which would appear to indicate stringent controls put in place in 1996 have been successful.
The Department said it was arranging for the destruction of the remaining animals in infected herds, which total more than 1,000 animals.
It has been the Department's policy to slaughter all animals on a farm where the disease is detected.
Since 1989 this has meant the destruction of 45,200 animals.
This process has cost the Irish taxpayer £55 million, including compensation to farmers and the transport, destruction, rendering and storage of the animals.
The new cases were found in two herds in Counties Clare, Cavan and Louth.
There were single cases in herds in Counties Limerick, Galway, Cork, Tipperary, Wicklow, Limerick and Kilkenny.