Cow manure has thrown Giro D’Italia preparations into chaos, with “half the peloton” struck down with severe illness.

The world-renowned cycling endurance race is due to start on Friday, but just getting to the start line is set to be a challenge for most of the competitors after taking part in an event in Belgium.

The Famenne Ardenne Classic was struck by wet weather on Sunday, with officials believing that cow manure splashed onto the cyclists during the event was responsible for infecting the competitors.

Three members of the Belgium outfit Lotto-Intermarche suffered from abdominal pain, diarrhea, fever and vomiting, and were briefly hospitalised in the wake of the one-day race, while much of the field has reported similar symptoms.

Lotto sport director Maxime Bouet claimed that “half the peloton is ill” as the team hope their riders can recover in time to start the Giro, which kicks off in Bulgaria.

There is no official cause for the outbreak, but Campylobacter, a type of bacteria responsible for gastrointestinal infections, is suspected to be the source.

A large number of teams involved on Sunday reported that the roads in the Ardennes race were contaminated with cow dung and tracks from farming equipment.