A first-half Johnny Matthews hat-trick helped Glasgow Warriors coast to a 50-8 BKT United Rugby Championship victory over Zebre.
JP du Preez, McDowall, Josh McKay, Thomas Gordon and Fraser Brown also went over for the Warriors.
Chris Cook scored the only try for the visitors.
Zebre flew out of the blocks and raced into a 5-0 lead before the game was two minutes old with scrum-half Cook scuttling over from a quick tap-penalty.
Tiff Eden did not manage the touchline conversion and the hosts recovered some composure to strike back through hooker Matthews, at the back of a line-out maul which had rumbled 20-yards to the try-line.
George Horne added the extras to edge Warriors into a two-point lead with 11 minutes played.
Zebre were in no mood to roll over, however, and it took some desperate cover defence from Sam Johnson and Ollie Smith to squeeze Luca Andreani into touch just a yard short of the line.
A side-entry penalty conceded by Warriors just inside their own half allowed Jacopo Trulla to edge the visitors back into the lead.
Warriors reverted back to the tried and tested, kicking a penalty to the corner for another line-out drive which was again finished off by Matthews.
That seemed to settle home nerves and they struck again on the half hour mark when Matthews latched onto a loose Zebre line-out then fed Du Preez.
The giant South African swatted aside two tacklers on his way to scoring.
The home team were now well on top without really hitting their straps as an attacking force.
In the last play of the first half, Matthews claimed his hat-trick by once again adding the finishing touch at the end of a powerful line-out maul.
That meant the bonus-point was in the bag despite Warriors having played well below their best.
Horne had missed his two previous conversion attempts but rediscovered his kicking antennae to nail the extra two points, which made it 24-8 at the break.
Warriors stretched further ahead after Scott Cummings charged-down Ratko Jelic’s box-kick clearance, and Rory Darge combined with Horne, who sent McDowall over.
McKay was next on the scoresheet, with the Kiwi winger racing home unchallenged on an overlap created by slick Warriors hands straight from a scrum.
With eight minutes to go, Gordon finished off a try under the posts following a powerful midfield surge from Sione Vailanu, and Brown powered home in the final play to bring up the half century of home points.
