12 Dec, 14:42
Prop Cian Healy is expected to miss the start of the 2014 RBS 6 Nations after undergoing surgery on his injured ankle on Wednesday.
Iain Henderson returns in the second row to partner Michael Kearney, while in the back row Dominic Gallagher comes in at openside with Jordi Murphy moving to the number 8 position.
The three changes in the back-line see the return of Ulster's Paddy Jackson and Luke Marshall at out-half and first centre respectively, while Andrew Boyle will start on the left wing.
Speaking from the team base in Italy, Ruddock said: "Following two very physical battles, we have turned our attention to a Scotland team that is much improved from the Six Nations.
"They played very well against England and play a very expansive offloading game. We will have to be at our best to beat them and that is our goal.
"I have made five changes to the starting line-up with experienced players like Luke Marshall, Paddy Jackson and Andrew Boyle coming back into the team."
IRELAND UNDER-20 Team & Replacements (v Scotland Under-20s, IRB Junior World Championship Pool C, Stadio Mario Battaglini, Rovigo, Saturday, June 18, kick-off 8.10pm local time/7.10pm Irish time):
15 - Tiernan O'Halloran (Galwegians/Connacht)
14 - Andrew Conway (Blackrock/Leinster)
13 - Brendan Macken (Blackrock/Leinster)
12 - Luke Marshall (Ballymena/Ulster)
11 - Andrew Boyle (UCD/Leinster)
10 - Paddy Jackson (Dungannon/Ulster)
9 - Kieran Marmion (UWIC/Exile)
1 - James Tracy (UCD/Leinster)
2 - Niall Annett (Belfast Harlequins/Ulster) (capt)
3 - Tadhg Furlong (Clontarf/Leinster)
4 - Michael Kearney (Clontarf/Leinster)
5 - Iain Henderson (Queen's University/Ulster)
6 - Eoin McKeon (Galwegians/Connacht)
7 - Dominic Gallagher (Dublin University/Ulster)
8 - Jordi Murphy (Lansdowne/Leinster)
16 - David Doyle (UCD/Leinster)
17 - Conor Carey (Ballymena/Ulster)
18 - Daniel Qualter (Buccaneers/Connacht)
19 - Shane Buckley (Garryowen/Munster)
20 - Peter du Toit (UCD/Leinster)
21 - James McKinney (Queen's University/Ulster)
22 - Craig Gilroy (Dungannon/Ulster)
IRELAND UNDER-20 POOL MATCHES (all kick-off times are local time) -
Friday, June 10: England 33 Ireland 25, Stadio Comunale di Monigo, Treviso
Tuesday, June 14: Ireland 26 South Africa 42, Stadio Comunale di Monigo, Treviso
Saturday, June 18, 8.10pm: Ireland v Scotland, Stadio Mario Battaglini, Rovigo