"This season we have maintained an open squad policy but besides that, the likes of Ronan has played in six of our last seven games," McGahan said.
"He was a replacement in the other game, Keith (Earls) the same. Paul and Doug (Howlett) have played seven straight, John (Hayes) the last five games and we're only in month two of a nine-month season.
"So there's a very good reason for maintaining the size of squad we have. We can't expect the same guys to play all the time.
"There are no more formidable places to go than Ravenhill and we fully recognise that. Ulster are a tough, robust side.
"But we have full confidence in our squad, in their ability to put their best foot forward to defend the good form we've shown up to now."
MUNSTER (v Ulster): Denis Hurley; Anthony Horgan, Barry Murphy, Lifeimi Mafi, Ian Dowling; Paul Warwick, Peter Stringer; Federico Pucciariello, Denis Fogarty, Tony Buckley, Mick O'Driscoll (capt), Donnacha Ryan, Alan Quinlan, John O'Sullivan, Justin Melck.
Replacements: Jerry Flannery, Darragh Hurley, Mark Melbourne, James Coughlan, Mike Prendergast, Jeremy Manning, Kieran Lewis.