Peter Dooley and George McGuigan return to the front row with the Byrne twins dropping back to the replacements bench, while in the back row Josh van der Flier comes in at openside flanker with Jack O'Donoghue the player to make way.
Conor Joyce, who captained the team against Fiji, reverts to the number 8 berth and Daniel Leavy, one of the try scorers last Sunday, completes a strong back row unit with John Donnan taking over from Sean McCarthy in the second row.
There are four changes in the back-line which sees the return of Adam Byrne to the right wing and captain Luke McGrath to scrum half.
With Tom Daly's tournament ended by a hand injury and Mark Roche listed among the replacements, Thomas Farrell and Rory Scannell make their returns to the starting line-up as the chosen centre pairing.
Speaking from the team base ahead of the TG4-televised fixture, Ruddock said: "This is a big game for both sides, the winner of this will have a guaranteed place in the semi-finals.
"We have a huge respect for New Zealand rugby and particularly their record at this age-grade level, but once the whistle goes on Thursday we will be as competitive as we can be to progress to the next round."
IRELAND UNDER-20 Team & Replacements (v New Zealand Under-20s, 2013 IRB Junior World Championship Pool B, Stade de la Rabine, Vannes, Thursday, June 13, kick-off 6.45pm local time/5.45pm Irish time):
15 - Darragh Leader (Galwegians/Connacht)
14 - Adam Byrne (UCD/Leinster)
13 - Thomas Farrell (Lansdowne/Leinster)
12 - Rory Scannell (Dolphin/Munster)
11 - Rory Scholes (Belfast Harlequins/Ulster)
10 - Steve Crosbie (Old Belvedere/Leinster)
9 - Luke McGrath (UCD/Leinster) (capt)
1 - Peter Dooley (Lansdowne/Leinster)
2 - George McGuigan (Newcastle Falcons/Exile)
3 - Christopher Taylor (Malone/Ulster)
4 - Gavin Thornbury (UCD/Leinster)
5 - John Donnan (Ballynahinch/Ulster)
6 - Daniel Leavy (UCD/Leinster)
7 - Josh van der Flier (UCD/Leinster)
8 - Conor Joyce (Malone/Ulster)
16 - Edward Byrne (UCD/Leinster)
17 - Bryan Byrne (UCD/Leinster)
18 - Adam Boland (Lansdowne/Connacht)
19 - Peadar Timmins (UCD/Leinster)
20 - Ryan Murphy (Dolphin/Munster)
21 - David Shanahan (Clontarf/Leinster)
22 - Mark Roche (Lansdowne/Connacht)
23 - Darren Sweetnam (UCC/Munster)
IRELAND UNDER-20S' IRB JUNIOR WORLD CHAMPIONSHIP FIXTURES/RESULTS:
POOL B -
Wednesday, June 5: Ireland Under-20s 19 Australia Under-20s 15, Stade de la Rabine, Vannes
Sunday, June 9: Ireland Under-20s 46 Fiji Under-20s 3, Stade de la Rabine, Vannes
Thursday, June 13: New Zealand Under-20s v Ireland Under-20s, Stade de la Rabine, Vannes, 6.45pm local time/5.45pm Irish time (live TG4/Sky Sports 3 red button/Sky Sports Xtra)
Tuesday, June 18 and Sunday, June 23
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