Two companies have gone on trial charged with health and safety breaches after an abattoir worker was crushed to death by a cow.

Merit Projects Limited and Sandyford Abattoir (Paisley) Limited went on trial on Monday at Paisley Sheriff Court following the death of Alexander McCrae.

The firms deny wrongdoing in how their employees installed, operated and maintained a cattle slaughter line at the slaughterhouse in the Renfrewshire town.

Mr McCrae, 23, known as Ally, was killed after being struck by one of the animals during his shift at the abattoir on November 17, 2011.

The worker, originally from Kilmarnock in East Ayrshire but living in Dumbarton, West Dunbartonshire, at the time of his death, was washing his hands when he was hit by the animal, which the court heard weighed around 102 stone.

A shackle carrying a cow carcass hit another one and sent it along the line at speed, the jury was told, bypassing the cow catcher and hitting Mr McCrae, causing him fatal injuries.

Merit deny four charges of failing to assess the hazards of machinery they supplied the abattoir; failing to draw up a technical file detailing calculation notes, test results and hazard elimination methods; failing to retain a technical file, and failing to supply a machine which "could not be misused" by the abattoir's employees.

Sandyford Abattoir deny three charges of failing to ensure the health, safety and welfare of employees; failing to make "a suitable and sufficient assessment of the risks to the health and safety" of their employees, and failing to organise, control, monitor and review how the size of their operation and the processes used would affect the health and safety of their employees.

Archibald Jess, a director of Sandyford, was the only witness to give evidence on Monday. He told the court Merit was chosen to install a new cattle slaughter line at the abattoir, which was up and running in October 2008.

The court heard Merit was involved in "snagging" - fixing minor problems - around March 2008 but Mr Jess said nobody from Merit worked on the beef line after it was installed, with work being carried out by engineers at Sandyford.

Under cross-examination from advocate Susan Duff, representing Merit, Mr Jess said he was unaware of any modifications being made between the line being installed by Merit and Mr McCrae's death.

He also dismissed claims a second stop/start button was added to the machinery, adding: "My understanding is it is as it was when it was installed on the day."

Mr Jess admitted the Health and Safety Executive sent prohibition notices to the abattoir after Mr McCrae's death as it emerged employees had been using a pole to "trip the system".

He said he was unaware his workers had been using a pole, adding: "They operated the way they were told to operate it in their training."

Mr Jess said he was unaware of claims the "cow catcher" - where the cow carcasses ended up - had been broken and repaired before Mr McCrae's death. He added he did not know Merit had been asked to replace a piece of the machinery just a month before Mr McCrae died.

The trial, before Sheriff James Spy, continues.