Wales' chief veterinary officer says it is possible that some cattle were infected with the Schmallenberg virus (SBV) and therefore anticipates "calving problems later in the year as a consequence."
Dr Christianne Glossop says since the first clinical case of the disease in Wales in November last year there have been a further 11 positive cases of SBV in sheep.
Dr Glossop is encouraging farmers to be vigilant for signs of the disease and to seek swift veterinary assistance if they have any concerns.
More top news
The three day annual event, held this year at Caerphilly castle is expected to attract thousands of visitors.
Dramatic footage of a near escape on the train tracks has been issued as part of the latest rail safety campaign
A mixture of cloud and bright spells for Bank Holiday Monday, remaining cloudy this afternoon