The presence of ammonia in stables, which is caused by the decomposition of a horse's urine and faeces, has long been a concern of horse owners and yard managers, and DIY liveries leaving stables un-mucked out until the end of the day has been the cause of many complaints. But there has been little scientific research to back up the link between respiratory problems and ammonia until now.

Research funded by The Horse Trust has found that stabling, regardless of bedding or forage types, results in increased levels of environmental ammonia and respiratory inflammation.

The research, which was led by Professor Sandy Love at the University of Glasgow, studied eight yearling Welsh Mountain ponies, who were serially alternatively housed then grazed for periods of three weeks. Three times each week, a variety of substances were monitored, including dust, endotoxin and ammonia within the environment, and the level of various gases and pH of the horse's exhaled breath. The forage and bedding within the stables were varied to test whether this had any impact on the pony or the stable environment.

Love found that the stabling of horses resulted in increased exposure to environmental ammonia and that this was associated with an increase in the pH of the horse's exhaled breath. Under the study conditions, no significant differences were found in ammonia levels under the different grazing and stabling conditions. Love was also able to confirm earlier research, that stabled horses are exposed to dust and endotoxins.

"Horse owners have long worried about the ammonia smell in stables, but there has been little scientific evidence to back this up. These findings confirm that ammonia is linked to poor respiratory health, although further research is needed to confirm whether and how ammonia causes respiratory problems," said Love.

It is unclear at present how ammonia impacts respiratory disorders in horses, but in other animals exposure to ammonia has been found to result in increased mucin production and reduced pulmonary clearance.

In the next phase of his research project funded by The Horse Trust, Love's team are carrying out a large-scale field study to quantify the environmental risk factors – such as bedding, feeding and ventilation – that predispose horses to respiratory inflammation. The results from this field study will be available next year.

"We are pleased that the research we have funded has improved understanding around the causes of respiratory problems in horses. We look forward to receiving the results from the final stage of Professor Love's research, which we hope will give horse owners practical advice about how to reduce the risk of this distressing condition," said Paul Jepson, Chief Executive and Veterinary Director of The Horse Trust.

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