Kettleborough and Donald set Glamorgan platform
Glamorgan 338 for 4 (Donald 91*, Kettleborough 81) v Gloucestershire
Opener Kettleborough contributed 81 to a total of 338 for 4 after his side had won the toss, while 18-year-old Donald made an unbeaten 91. Chris Cooke chipped in with 65 while James Fuller was pick of the home attack with two for 42 from 16 overs.
The visitors were initially made to work hard for their runs after a wet outfield delayed the start by an hour until 11.30am. By lunch, Jacques Rudolph and Kettleborough had taken the score to 22 without loss from 14 overs.
Fuller extracted some lift from the Ashley Down Road End, while left-arm seamer David Payne, last-over hero of the Royal London One-Day Cup final victory over Surrey, repeatedly swung the ball away from left-hander Rudolph.
The afternoon session saw Rudolph pinned lbw for 17, surprised by a Payne inswinger, while Fuller picked up the wicket of Colin Ingram, caught behind driving for 30.
At tea, 22-year-old Kettleborough was unbeaten on 78, having overtaken his previous best score of 73, made for Northamptonshire against Middlesex at Lord's last season.
His half-century had come off 82 balls, with 10 fours, after he had been dropped in the slips off Tom Hampton on 18 following a short rain break.
Glamorgan had reached 161 for 2 from 44 overs at tea, with Donald on 26. He added 56 with Kettleborough, whose hopes of a maiden century were dashed when he was caught behind pushing defensively at Payne, having faced 127 balls and extended his boundary count to 14.
At 165 for 3, Cooke's arrival to join Donald saw the scoring-rate accelerate as they went on the attack against Hampton and Kieran Noema-Barnett, adding 101 in 18 overs.
Cooke raced to a 54-ball half-century, with 8 fours, after Donald had reached the same landmark from 70 deliveries, neither offering a chance.
It was a surprise when Cooke fell to a top-edged pull-shot off Fuller, safely pouched by Payne at fine leg with the total on 266.
Donald kept his composure to still be there at stumps just nine short of a maiden century, having faced 122 balls and overtaken his previous best first-class score of 67, made against Essex at Chelmsford this season. David Lloyd was unbeaten on 29.
Another shower took the players off briefly before the close and in all 19 overs were lost to the day's play.
Gloucestershire wicketkeeper Gareth Roderick was forced off by a hand injury in the final session. Academy player James Bracey, 18, replaced him with Glamorgan's permission.