Cowgill, who was sent down in the wake of Tuesday starter Tyson Ross' promotion, will head to Sacramento alongside right-handed reliever Andrew Carignan, who was also officially optioned and replaced on the roster by callup Neil Wagner.
With Cowgill out of the mix, the A's still have five outfielders on their roster, a number that helped along a tough decision for manager Bob Melvin.
"That was a difficult one," he said. "The fact is we had six outfielders here and I just wasn't able to get Collin as many reps as I would like. When you tell a guy like that he's going down, I really have no reason to tell him he's going down, because he did everything we asked. It was just a numbers game.
"From the day he got here, from Spring Training until all the way up until today, he's impressed everybody in this organization, from his teammates, coaches, front office, myself. So it was a difficult one to make but one we had to."
Cowgill appeared in just three of the club's first 11 games, going hitless in four at-bats while posting a .429 on-base percentage thanks to three walks. Melvin particularly appreciates the 25-year-old's all-out style of play, which he anticipates returning to Oakland this season.
"Depends on what happens, whether it's injury or whatever," he said. "I would expect him back here at some point in time, but at this point I don't have a reason for it yet."
In the meantime, first baseman Kila Ka'aihue -- greatly speculated to potentially be designated for assignment on Tuesday -- remains with the A's, as Melvin noted they'll need another first baseman around for the times Daric Barton rests. Ka'aihue's offensive performance also earned him more looks, with the infielder entering the day batting .467 in four starts.
Ka'aihue also lends the A's a pinch-hit option in the later innings, and while he could conceivably start at DH from time to time, Melvin said the majority of those at-bats will go to Seth Smith and Jonny Gomes.
"He's done a nice job for us, and Barton's going to need some days off," Melvin said. "Kila has certainly done well enough to fill in for him."
Wagner, meanwhile, is embarking on his first stint with the A's this year, having posted a 5.06 ERA in three relief appearances spanning 5 1/3 innings for the River Cats. But he did not walk a batter during that span and struck out eight. Familiarty reigned over numbers when it came to decision time, Melvin noted.
"He's a guy that was here last year and we expect him to make strides this year," he said. "He was kind of in the same situation Carignan was and Carignan pitched better this spring and now Wags is back and probably more so in a length role at this point."