Harness Racing NSW (HRNSW) announced the inquiry today, which will date back until January 1, 2013.

The inquiry started following concerns that a number of horses trained by Hillier were being presented to race with elevated TC02 levels.

The threshold for TC02 is 36 millimoles per litre in plasma, but an allowance of one is added for instrument error, meaning horses must swab 37 to produce a positive.

HRNSW Manager Integrity and Chairman of Stewards Reid Sanders travelled to Wagga for the start of the inquiry on Thursday.

Sanders said none of the Hillier team had a swab over the threshold, but there were a number of "highly elevated" samples.

Because of this information HRNSW stewards attended the Hillier stable on August 2, the morning five Hillier horses raced at Albury.

"We had staff at their premise for a period of time and got what we call controlled samples," Sanders said.

"Comparing those to race day samples, we have some concerns about husbandry practices leading up to those horses being presented to race."

Although no positive swabs being recorded, Sanders indicated that other methods are open to HRNSW.

"We are considering whether there has been a breach of the rules in other ways," he said.

"How the horses actually got to those levels and there has been expert evidence about the only way horses can technically reach that level if they are not a naturally high horse."

In the inquiry evidence including the swab history reports of horses trained by Hillier was presented.

HRNSW Regulatory Veterinarian Dr Wainscott also gave expert evidence.

The inquiry was adjourned until September 18.

Hillier has not been stood down and had six runners including two winners at Wagga today.

She also has two runners at Menangle and five at Young tomorrow.

She did not answer calls from The Daily Advertiser.