The Comrades Marathon Association has also expressed concern, saying it is monitoring the air pollution ahead of the world’s most popular ultra-marathon in June.
The stench is from the Shongweni landfill site - very close to Summerveld - but the operating company, EnviroServ has denied that it is the sole source.
Residents from Kloof, Dassenhoek, Hillcrest, KwaNdengezi, Shongweni and Assagay say they have complained about the smell for two years but nobody has listened.
Summerveld Estate manager Tony Rivalland said the past two years had been difficult with horses continually coming down with unusual aliments.
“Racehorses suffer from nose bleeds but, of late, horses are suffering from nose bleeds without being involved in strenuous exercise or injuring themselves.
“We’ve had some horses with bleeding noses while they are in a box and those that are coughing are taking longer to shake off the coughs, even on treatment.”
Gold Circle’s racing and marketing executive Graeme Hawkins said they were working with trainers and vets to monitor the situation.
“We may not be able to prove it scientifically but we are worried that the fumes are the cause of the respiratory and haemorrhaging incidents and that this could impact on racing,” he said.
Rivalland said many of the 550 grooms complained of itchy eyes, rashes and sore throats.
“We cannot prove that the fumes are the cause but we strongly believe there is a correlation between the fumes from the site and the symptoms in people and horses.”
Every year the estate houses an extra 130 horses from Cape Town who stay for four months to acclimatise ahead of the big races - the Vodacom Durban July being one.
“It’s difficult to say if they will be affected but one thing I know for sure is no one wants to live with a stench like this on a daily basis,” said Rivalland.
Hillcrest became the hub of KwaZulu-Natal horseracing activities after the closure of Clairwood Racecourse in 2014.
Comrades Marathon Association general manager Chris Fisher said they hoped the issue would be resolved before the race in June.
“At the moment we can’t say for sure that it will affect the race but we will monitor the situation.”
Athlete Sizwe Ngubane said he couldn’t train in the area.
“I felt sluggish all the time and my sinuses acted up. It’s not wise to expose our pro-athletes to that. Possible damage to their lungs could ruin their careers. When I run Comrades I don’t want to run through that,” he said.
He said he thought athletes might pull out of the race if the issue remained unresolved.
Last year residents lodged formal complaints about the bad smell with the Department of Environmental Affairs which prompted an investigation.
The Green Scorpions also initiated a criminal investigation after a search and seizure warrant was executed at the landfill site in September.
“It was found during the search that EnviroServ Waste Management (Pty) Ltd had failed to comply with the provisions of environmental law and certain conditions of the waste management licence,” said department spokesman Albi Modise.
A further notice was issued by the department citing the continued complaints levelled at the site as reasons to revoke or suspend the operating licence.
“We believe the department’s notice is legally, technically and procedurally flawed and have submitted our motivation as to why it should not be revoked or suspended,,” said EnviroServ’s chief executive Dean Thompson.