Teams in the inaugural Rainbow Cup will be able to replace players who are sent off under trial laws being brought in for the tournament.

In the last five minutes a captain can challenge any decision, provided he has not made a previous challenge.

In addition, when attackers are held up over the try-line, the defending team will drop out from their goal-line.

The rule will also apply to in-goal knock-ons and when defenders ground the ball from attacking kicks.

Under existing laws, attacking teams are awarded a scrum five metres from the opposition try-line when they are held up.

When a player is sent off, his team will be down to 14 men for 20 minutes before he can be replaced by another player.

The three experimental laws have already been used in New Zealand's Super Rugby Aotearoa and the Australian version of the competition.

World Rugby chief executive Alan Gilpin said: "We applaud Pro14 Rugby and the respective clubs for their enthusiasm to trial a number of law variations in the Rainbow Cup.

"The addition of another top competition to the World Rugby law trials programme will provide invaluable data and feedback to determine future advances to game spectacle and player welfare."

Pro14 tournament director David Jordan said in the statement announcing the trial laws: "We know these laws also have their origins from the player welfare symposiums and our belief is that we will see a positive impact on the game overall."

The Rainbow Cup - involving teams from Wales, Ireland, Scotland, Italy and South Africa - starts on Friday, 23 April, with derby games in the five countries in the opening three rounds.

Ulster host Connacht on the opening night while in Wales Cardiff Blues travel to Ospreys the following day.